How to Control Moisture Coming Up Through the Concrete Floor?

Water is an inherent part of the hydration process of concrete. However, allowing excess moisture to leave the slab after it’s poured is crucial to a successful flooring installation.

Here is what you’ll learn in this article to have a successful installation:

Once the slab is poured, the excess moisture must be left to strengthen the concrete bond. The slab must also dry to a specified moisture level before installing flooring materials. Moisture-related damage to the flooring materials is possible.

3 Common Flooring Materials Run The Risk of Moisture-related Problems:

1. Adhesives

Moisture-related adhesive failures are a problematic reality in the flooring business. Recent trends toward restricting volatile organic compounds (VOCs) in flooring adhesives have increased the number of moisture-sensitive adhesives used. If the adhesive used to install the flooring does not have the correct moisture tolerance for the concrete subfloor, the entire installation can be at risk.

2. Floating Floors

Floating floor systems are attractive because they don’t need to be attached directly to the subfloor. Instead, the floor pieces “lock” together to become a cohesive unit less vulnerable to seasonal shifts, dimensional challenges, or other moisture-related issues. In fact, floating floors are often recommended on projects with high moisture risks with standard attached floor systems.
Laying Ceramic Tiles
For floating floors, manufacturers often recommend installing a moisture barrier between the subfloor and the floating floor to prevent moisture intrusion. The difficulty, of course, is that if the moisture barrier is compromised in any way, moisture from the slab beneath can still damage the flooring or finish.

3. Grout or Cementitious Bonds

Excess moisture issues in a grouted tile or mosaic floor often appear as efflorescence, a whitish residue on the surface of the grout. It’s the result of water-soluble minerals getting transported to the surface of the grout with moisture as it evaporates away. Since minerals don’t evaporate, they’re left behind on the floor surface as a visible residue.

The more porous the concrete or grout, the more likely efflorescence will appear. In the majority of cases, these minerals are part of the concrete slab mixture. Although they can possibly be in the ground beneath the slab and seep into the concrete if no moisture barrier was installed. If the slab were not dried to the required specs before the tile was installed, the natural moisture migration of the drying concrete would impact the grout.

Remediation steps will be necessary to correct the problem. In extreme cases, excess moisture can lead to flaking or chipping the grout, resulting in a complete grout or thin-set failure.

Are you seeing a theme yet? The real risk to a successful floor lies with the moisture that can accumulate within the layer between the concrete slab and the flooring itself.

Adhesives, floating floors, and grout or cementitious bonds are 3 common flooring materials that can run the risk of causing moisture-related problems. Moisture control is often one of the most crucial yet overlooked elements of any floor’s success over time. Responsible moisture control (having accurate moisture measurements) starts with the concrete slab.

Make sure to use the most accurate concrete rh test from Wagner Meters.

Shop Rapid RH L6

moisture in subfloor

Click to watch and learn more about moisture problems between flooring and slab.

Moisture in a Concrete Subfloor

It must reach that middle layer for moisture to accumulate between the concrete slab and the flooring. In this section, we break down the main ways water can get into your concrete, which causes a buildup of excess moisture, and list effective methods to prevent moisture problems from occurring.

4 Sources of Moisture in Concrete Floors

The primary source of moisture in a concrete slab is the proportion of water mixed with the cement. No water source has a greater impact on the time it will take concrete to dry.

Yet you have other water sources to worry about. Potential external water sources at a worksite can affect slab drying and curing.

1. Weather and Elements

Rain, snow, and sprinkler systems are culprits on a work site open to the elements. These water sources increase in danger if the grade of the grounds around the slab slope towards it. Not only is the concrete absorbing the water from above, but it’s also taking on the runoff from the areas around it.

2. Groundwater

The concrete slab can also absorb the groundwater below and around it. Thus, the amount of natural groundwater greatly impacts concrete moisture conditions.

3. Unnatural Sources

Unnatural water sources can also leak water. Any poor plumbing installation at the worksite creates a high risk of excess moisture. Old plumbing that’s degraded and has leaks presents the same risk.

4. Ambient Conditions

Ambient conditions can also increase the concrete slab’s water content. Condensation develops on a slab with a lower temperature and moisture level than the air’s dew point. The dew point is the temperature at which the air can hold no more moisture. You know, when dew (or condensation) starts to form. The slab will absorb some of the condensation.

The slab will also absorb moisture from its environment when its relative humidity (RH) is below the air’s RH. Moisture wants to level out. If the air holds more moisture than the slab, as evidenced by its RH, it will move to the concrete.

Rain, snow, groundwater, leaks, increasing water content, and sprinkler systems are all potential sources of free water. That is, water the concrete doesn’t need to cure. Any moisture the slab doesn’t need is moisture that can undermine your flooring installation.

What Are Causes of Excess Moisture in a Concrete Slab

Inadequate drainage around the slab exacerbates the risk of any source of moisture. In fact, the existing water source itself may not be the problem. A little rainfall or some groundwater can drain away with well-designed drainage. Even minimal water sources can pool on the concrete without adequate water lines and drains.

Excessive water can also intrude into a structure due to poor subfloor protection. Groundwater will move into the concrete if no vapor retarder sits between the ground and the subfloor.

1. Using the Wrong Vapor Retarder

The more likely cause for poor subfloor protection is using the wrong vapor retarder. Certain ASTM standards allow a vapor retarder to have a perm rating of 0.3 perms, which could allow up to “approximately 18 gallons of water per week in a 50,000 square foot area.” A vapor retarder with too low a perm rating won’t do the job it needs to do.

The vapor retarder may have been sitting on the ground in other cases. It’s helpful to have a separation barrier between the ground and the vapor retarder. Contractors should install the vapor retarder over granular fill to create extra separation from the groundwater.

2. Damaged Vapor Retarder

A torn vapor retarder is another potential hazard to subfloor protection. Torn vapor retarders can occur in a reckless worksite. Hurried construction schedules create all sorts of moisture (among other) threats.

3. Not Enough Time to Dry

Fast-paced project plans often mean that concrete slabs don’t have the time to dry. For example, slabs may get power troweled to speed up preparations for flooring. The compression caused by the troweling closes off the evaporation outlets in the slab. The result is that over-troweling will extend the drying time.

If the schedule doesn’t allow that time, adhesives or surface membranes get installed on concrete with too much moisture. A moisture-related flooring failure is practically guaranteed under such circumstances.

Free Download – 7 Things You May Not Know about Concrete Slabs

How to Avoid Excess Subfloor Moisture

To effectively avoid excess subfloor moisture, it is crucial to conduct accurate concrete moisture testing. Inaccurate moisture testing can occur in two primary ways.

1. Choose the Correct Moisture Test

Selecting an inappropriate concrete moisture test can lead to inaccurate results. The in situ relative humidity (RH) test, which measures moisture beneath the slab’s surface, is the most reliable method. Tests that only measure surface moisture may yield incorrect data.

3. Use the Correct Amount of RH Sensors

Improper execution of the in situ RH test can also result in inaccurate results. To obtain a comprehensive understanding of the area, ensure an adequate number of sensors are placed throughout the floor. According to ASTM F2170 guidelines, three sensors are required for the first 1000 square feet, with an additional sensor needed for every subsequent 1000 square feet. Other testing mistakes, such as incorrect sensor depth insertion, can also impact accuracy.

Even minor errors like misreporting readings on a chart can lead to serious consequences. Wagner Meters’ Rapid RH® L6 sensors feature integrated data storage for automated results reporting, eliminating the need for paper notes during decision-making meetings about flooring installation.

Always use the most accurate concrete RH test from Wagner Meters to ensure you avoid excess subfloor moisture.

Shop Rapid RH L6

How to Prevent Subfloor Moisture Issues

Moisture is an inevitable part of concrete construction. Moisture-related problems are not.

1. Keep a Low Water-to-Cement Ratio

The more water in the mix, the greater the chance the slab won’t get all the time it needs to dry. Try to avoid adding water to concrete that’s already mixed. Water is a new variable that makes managing timelines and moisture issues difficult.

2. Pour Concrete Below Grade

Take all necessary actions if pouring concrete below grade or at a wet building site. Whether that means installing more draining lines, using pumps to dewater the site, or any other method – do it. Ensure your water displacement methods aren’t generating run-off in the wrong directions.

3. Prevent Water Seepage

The layers above and below the concrete slab prevent water seepage into the slab. Start with a vapor retarder with a perm rating that reflects the needs of the space. Install it over a layer of fill.

Inspect it before pouring the concrete and fix any tears it may have. Use a proper underlayment between the concrete slab and the flooring if necessary. This is especially true when using wood flooring. Installing a plywood underlayment can add extra protection, but it must also be tested to ensure it’s not bringing in new moisture.

4. Give it Time to Dry

Give the concrete slab the time it needs to dry and cure. Review the project plan and schedule. Is enough time set aside for concrete floors to dry? No reason to start out behind the eight ball. Exert as much control over the ambient conditions to accelerate the timeline.

Protect the space from outside elements. If the season isn’t ideal, can you take steps to reduce swings in air temperature? Will a dehumidifier help the air absorb more moisture from the concrete? Use fans to increase airflow, which speeds up drying time.

All these methods point towards a single goal: not installing any flooring too soon. Preparatory materials like adhesives or plywood will seal up the concrete. Sealed concrete will stop releasing moisture. At that point, the slab has the moisture it will hold for the long term. If there’s excess moisture trapped in the concrete, it will eventually reveal itself in ugly and possibly dangerous ways.

Low water to cement ratio, using pumps to dewater, not using a vapor retarder, and not allowing concrete to dry and cure adequately are all ways to prevent moisture problems on concrete floors.

How to Tell If There Is Excessive Moisture in My Subfloor

A floor may already be showing some external signs of containing excess moisture. A floor with a white or greyish powdery stain (also called “efflorescence”) likely has excess moisture due to moisture moving up through the slab and then evaporating from the surface.

The whitish stain is the salt left behind by evaporating water. Or you may see that the flooring installed over the concrete slab is blistering or peeling away. If wood flooring has been installed on top of the slab, the wood may be cracking or warping.

These flooring failures occur due to excess moisture trapped between the flooring and the concrete.

No one wants to wait until the ugly signs of excessive moisture are visible. You want to know if your floor is holding too much moisture well before that.

Excess moisture is caused by a number of ways a few being: the hardwood floor is cupping or cracking, you see efflorescence or a white residue on the concrete floor, or the floor over the concrete is blistering or peeling away.

Moisture Management Requires Accurate Moisture Readings

Accurate concrete moisture measurement is only achieved with RH testing. Unlike surface-based tests like calcium chloride tests, RH testing determines the accurate moisture condition within the slab by placing probes at a strategic and proven depth.

Moisture often rises through a slab from the bottom to the top during drying. Only testing performed at the correct depth can let you determine if the final moisture condition of the slab will be compatible with the flooring and the products used to install it.

Total Reader and Test Results Form

Wagner Meters has been assisting flooring professionals for over 50 years. During these decades, we have designed some of the most accurate, innovative, and easiest RH testing sensors today. The Rapid RH L6 is the newest iteration, using 21st-century technology to simplify reporting.

All our Rapid RH sensors and test kits are based on decades of scientific research and technological advances to help each builder and flooring specialist accurately determine the correct concrete RH level for a project’s chosen flooring materials. Our innovative Total Reader® and factory-calibrated Smart Sensor design delivers quick, reliable results.

The Rapid RH line of products is affordable and conforms to ASTM F2170 requirements for easy recording and reporting.

Along with accurate, actionable testing, we’ve also compiled a one-stop list of manufacturers that provide an RH tolerance specification for their flooring products at

Last updated on May 1st, 2024


  1. Kim Rike says:

    I live in metro Colorado. My house was built in 1999 with a 1699 sf concrete basement. In 2015, we built out our basement and had rubber gym flooring installed over the concrete to create a gym area. We’ve lived here 12 yrs and have had no moisture issues with the basement concrete until this week.

    This week, we found moisture pooled underneath the rubber gym flooring where a rubber yoga gym mat sat atop a cheap rubber/vinyl (?) yoga mat on top of the gym flooring. When we stepped on the mats we noticed moisture pooling up through the rubber gym flooring on either side of the mats. When we lifted the mats, we saw that a decent amount of moisture was sitting on top of the rubber gym flooring. After drying the moisture on top of the gym flooring, we found there was still a significant amount of moisture underneath, between the rubber flooring and concrete. That is, when pushing down on the rubber flooring, more moisture would ooze up through. We’re using fans and towels with heavy weight on top to draw out and dry up the moisture.

    The moisture was only found in that one area of the gym floor, under the 2 mats. We pressed on other areas of the flooring and found no moisture under the treadmill, other gym equipment, or other parts of the floor. We believe the moisture may have been created from humidity, that in turn may have been created form a combination of our big temperature swings this time of the year and the 2 rubber mats piled on top of the rubber gym flooring. Does that sound plausible, or should we be concerned there’s a bigger problem?

    Any advice is helpful.

    • Jason Spangler says:


      That could definitely be plausible. I am surprised though that you aren’t seeing at least a small amount of moisture around some of the equipment. Not sure what type of gym flooring you have down, but if it isn’t adhered to the concrete, it may be worth trying to pull a couple of pieces up to make sure there is moisture below. Good luck.

  2. Ashmore Carpets says:

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  3. Evelyn Pino says:

    We had marble tiles installed in our entrance, hall and kitchen. Just the kitchen grout started to crumble after about three years. We had another floor installed because the cement dried that was holding the tiles down. They used the same tiles and after not even a year the tiles can be picked up and the cement holding them down is dried. Can you tell me why please.

  4. Denise A Goble says:

    We moved into a home in South Florida 7 years ago. One of the rooms has what looks like ‘laminated’ wood flooring. There was what looked like a stain in one of the children’s bedroom. I have used this room as a sewing room and have always had binds laying around and near the outside wall.
    I had to move the bins and was surprised to see that ‘stain’ has gotten larger and I want to know who would I should call to come and determine the problem. The floor is not wet or damp to the touch, but I think moisture is coming up through the cement slab somehow.

    Please give me some direction.

    Thank you,

  5. Joe Palombo says:


    I have a ’75 built split level with slab on grade. No insulation under the slab. We just purchased the home in august and humidity is pretty high on the first level during summer (CNY). I ripped up a few planks of the LVP the original owners installed to find mold/mildew under the vapor barrier as well as condensed moisture BETWEEN the LVP and the vapor barrier. The concrete also felt a little damp and they appeared to try and ‘seal it with some sort of paint.

    Going forward, I plan to properly grade around the house and install swales and perimeter drains in the spring. For a new floor, I’ve been reading about so many different options including DRIcore, Delta-FL, etc. One solution that has come to mind is the need for a much higher R-Value between the floor and the slab. A proposed solution was a layer of poly, then rigid foam, then plywood. They want the foam layer as sealed as possible. If moisture is just being sealed into the slab, isn’t it possible it just wicks into the sill plates and studs, rotting them out over time?

    Does anything mentioned above, outside of the fixed landscaping, sound reasonable?

    • Jason Spangler says:


      Thanks for the questions. So the first thing you need to determine is the moisture condition of the slab. This is usually done with either a relative humidity test like our Rapid RH L6 or with a Calcium Chloride test. This will help you understand the current condition of the slab. Second, you need to try and quantify the “humidity is pretty high” comment to determine the possibility that the moisture between the vapor barrier and the LVP might be dew point condensation. This may require some type of dehumidification unit in the house. You may need to have a multi-pronged approach to try and help this issue. I think your idea of ensuring proper drainage is a good one. Good luck.

  6. Mick says:

    Hi Jason,
    I recently moved into a home that was built in 1961. We had to pull out the old basement flooring and stripped it down to the concrete about 4 months ago.
    We were going to put new flooring down, but noticed that the concrete moisture levels were high. For 2-3 months we had industrial dehumidifiers and fans in our basement trying to dry the concrete, but it did not work. We also searched for plumbing leaks, but nothing. We have not noticed any water coming into the basement from the outside, though our sump pump will occasionally go off after a heavy rain.
    We do not think this house has any type of vapor barrier under the concrete due to the age, and after many attempts to fix the moisture problem, we believe the moist concrete is due to the lack of a vapor barrier.
    We would like to proceed with installing a floor eventually, but we have gotten so many conflicting options on how to proceed.
    Would you recommend adding a vapor barrier covering over our concrete? If so, should we use a vinyl-type plastic or possibly use an epoxy-like painted on sealant.
    Also, what floor would be best on top of that?
    Thanks so much for posting all of your articles, they have been very helpful!

    • Jason Spangler says:


      Thanks for the question. My recommendations will be general, but in my opinion, some type of epoxy mitigation system would probably be your best bet. Just make sure you research the functionality of the product on a slab without an effective vapor retarder and potential hydrostatic pressure (which a basement can have). Many have clauses that exclude slabs with these potential characteristics. Some of the bigger name products to research are from Ardex, Uzin, Mapei, Koster, AcTech. I hope this helps.

  7. Donna says:

    I have a question
    My husband & I looked at a house in northwest Ohio built in 1966 and is on a cement slab
    They installed new flooring & fresh paint & had installed new footer tile along back and sides of house . Ran the tile to catch basin in front yard. backfilled tile with stone around the house .
    Ran a tile and connected 4 downspouts into it and hooked it into footer tile out by the basin
    So my question is do you think this is a good thing or are they trying to cover up something?
    I’d greatly appreciate your answer
    Thank you ,
    Mrs. Reed

    • Jason Spangler says:

      Mrs. Reed:

      Thanks for the question, but I can’t answer it with any level of certainty. If I were going to guess, an older house of this nature didn’t have proper drainage when it was built initially and they are trying to make it better. The lack of proper drainage MAY have caused some issue with the flooring and paint so they fixed the problem and the symptoms. Again, just my opinion. Good luck.

  8. Michelle Brown says:

    Thanks for the reply Jason,

    I have been reading TONS of info about concrete slabs and moisture problems. I have called and talked to a few specialists. One opinion I keep getting is to seal the slab with a 2 part epoxy sealer. This will “seal” the slab and prevent moisture from entering up into the house. It’s costly as they have to come and grind the slab first in preparation for the sealer. Do you have any opinion on this avenue of protection? The grading oh my home is excellent as there is at least 6 to 8 inches of slope away from the foundation to the outside yard, and all drainage is buried to be sent to outside of the yard into drainage ditches in my neighborhood which is why I’m so baffled by this situation.

  9. Michelle Brown says:

    Hi Jason,

    I’ve read all the reply’s and it’s a bit overwhelming to be sure. My house is on slab and is 27 years old. I bought the house 3 1/2 years ago. There was carpeting throughout and I had LVP run throughout the house. Well, I’m doing a kitchen remodel. The contractor went to remove a few planks of the LVP to lay the same flooring in the kitchen and found moisture, and mold. It’s LVP with a cork backing. No barrier was applied under the LVP. IT seems that the floor is only moist in certain areas though and nowhere near where there could be any leaking. So I don’t know what to do. I paid 15K for the whole house to have LVP 3 and 1/2 years ago before I moved in. The contractor said to stop as he suspects this mold is under all the LVP and to call Insurance. He said when he pulled up the carpeting there was no previous moisture issues noted on the old carpet. This seems to be a problem given other replies with LVP. Maybe concrete slabs just need to breathe and the LVP stops that, therefore creating these moisture issues? Now I don’t know what flooring to install…. Any advice would be much appreciated.


    • Jason Spangler says:


      Thanks for the questions. LVP as a product isn’t the issue necessarily. It ensures the slab is appropriate for the LVP before the installation. This may be by moisture testing and/or some type of topical barrier between the LVP. It just depends on the manufacturer’s requirements. As I always recommend, pick the floor you want and then do your due diligence on manufacturer installation requirements for the given product. Find their installation documents and see what is required when installing on concrete. Once you know this, ensure the contractor you chose is willing to do it. Good luck.

  10. Tonia Zanders says:

    My home is 30 years old and I had floating floors installed and withing 4 months they began yo warp. Found out the contractor failed to do a moisture test. I had a floor inspection and my concrete sub floor came in at 100% moisture. Even with a moisture barrier they indicate I will continue to have problems. How do I correct or is there a remedy for such a high concentration of moisture? There is no evidence that the excess moisture or water leaks is coming from my home.

    • Jason Spangler says:


      Sorry for the issues you are having with your floors. I recommend that you call the manufacturer of the flooring you had and/or are having installed and explain the situation and see their recommendations. Some products can be applied to the slab to slow down the amount of moisture that reaches the surface, so finished flooring can survive, so I would ask them for direction. If, for some reason, they can’t or won’t give you direction, find a flooring manufacturer that will. Floors are installed with moisture level that high and succeed if installed with the appropriate products. Good luck.

  11. Melissa says:

    Jason thank you for all this info it is so helpful to know I am not alone in my floor moisture issues.

    My Florida home was built in 1981 and we have lived here for 27 years. Almost 4 years ago we installed porcelain wood plank tile throughout our living area, kitchen and hall. About a month after installing we noticed efflorescence and then small droplets of water coming through the grout line. The previous flooring was 12 x 12 tile in the kitchen and carpet in the living area and hall. When this was pulled up we did not noticed and moisture issues in the house but have lots of moisture in the garage flooring.

    We have had leak tests done, foundation tests, installed new gutters, installed French drains, and applied water proofing to the sides of our house. We have come to the conclusion that our vapor barrier was either compromised or not installed at all.

    We have had many flooring companies come and we have many different thoughts. One said until the moisture is below a certain level nothing can be done and another said they can use Mapei aqua defense and this will make it possible to put In luxury vinyl. So said epoxy.. I am worried if I seal the floor will the moisture then go under the walls or cabinets?

    We still see moisture if you put a plastic tote on the floor and it can’t breathe and efflorescence still in some areas.

    Help, this has been way too long and after paying to have all my tile removed and my floor sanded I’m afraid to trust anyone.

    • Jason Spangler says:


      Sorry for all of the problems. With everything you have done to determine and/or fix an excessive moisture issue in your concrete, I still didn’t hear a “concrete” (no pun intended) moisture test result that anyone has done to determine a solution. The symptoms you describe sound like excess moisture, but how much excess? The Mapei product you explain isn’t meant to be a moisture mitigation product; it is a waterproofing product. They are different. This specific Mapei product you called out has this in its technical documents:

      Do not use where excessive substrate moisture and/or where negative hydrostatic pressure exists. Maximum allowable moisture is 8 lbs. per 1,000 sq. ft. (3.63 kg per 92.9 m2 ) per 24 hours per ASTM F1869 or up to 85% relative humidity as measured with moisture probes.

      So, there is still a test that needs to be performed. If you are looking for a moisture mitigation product (one that slows the moisture from coming out of the slab to an acceptable level for flooring installations, you may want to look at 1_3000968-planiseal-vs-en_1ef388075d2e4779ab46cb81c3225acc.pdf ( There are many of these epoxy moisture mitigation products available, I just chose the Mapei product because you had brought up that specific manufacturer. As far as the walls and cabinets, moisture moves very little laterally in concrete, so the chances are minimal.

      In case the link didn’t work:

      Good luck.

  12. Kimberly Williams says:


    Plano Texas. 1979 home. Prior to our purchase, LVP floor was installed on concrete slab without moisture barrier as part of renovations.1.5 years after installation buckling of the floor occurred. We have had testing and there is no slab plumbing leak, we had sprinklers tested no leak, and performed grading of our soil and dropped the soil level to expose appropriate four to six inches of slab.

    The flooring was removed and our slab has been exposed for 4 weeks. The moisture content along some perimeters of rooms is still 6% with a concrete moisture meter. We have been unable to find any source for moisture. There has been no condensation seen on the slab since it has been exposed for the last 4 weeks. I have tried unsuccessfully to find someone in my area who can perform definitive in situ relative humidity testing.

    We would like to move forward with installing new LVP flooring. The flooring company has proposed using a 6 mil poly moisture barrier per manufacturers recommendation for concrete slab installation.

    Is there anything else we have not looked for as a source? Is it possible the vapor barrier will be enough? How do I know if they are installing the vapor barrier correctly?

    • Jason Spangler says:


      Thanks for the questions. My recommendation would be to contact the manufacturer and discuss your specific situation and verify if the 6 mil installation will give you a warrantied installation if done properly. If the answer is yes, I would then ask them about the proper process for the 6 mil installation so you can verify. Good luck.

  13. Josh Talamo says:

    We have a floating vinyl floor that we laid over stained concrete. Flooring delaminating caused us to have to pull it up. When we did we found a white substance on the concrete that’s in the shape of the planks. We believe this is efflorescences?

    RH in home is 40%

    3 calcium chloride tests and have a range of 1.5 – 4.4

    Would a crack suppression membrane or primer help dissipate the moisture being trapped between the concrete and vinyl if this is the case and do these readings cause us to need to do anything ?

    • Jason Spangler says:


      Thanks for the question. If you are going back with the floating floor, I would consult the manufacturer. Many of those types of floors require, at minimum, a 6mil polyethylene plastic sheeting installed underneath the plank. Good luck.

  14. Lindsay says:

    Hi Jason,
    I live in south FL.
    1 year ago I had luxury vinyl flooring installed in my bedrooms. The installer leveled off the floors by installing plywood underneath the vinyl and on top of the concrete. 1 year later there is mold and moisture underneath the floors and we had to remove everything.
    I called numerous leak detection companies who cannot find a leak or any water coming in from the outside of my home. Do you think the issue is related to the installer not using a vapor barrier to seal the concrete prior to installing the flooring?
    The flooring has been removed for 2 weeks but the concrete is still showing high moisture levels in some areas. the mold remediation company has had fans running for the last 7 days to dry out any moisture.
    I am worried about reinstalling the luxury vinyl flooring if there is still moisture in the concrete. How much moisture is normal to have in concrete? Please let me know if you think a vapor barrier is the answer to my problem, and if you can recommend a vapor barrier brand.

    Thank you!

    • Jason Spangler says:


      Thanks for the questions. First, you don’t typically see plywood used over concrete to “level off” the floor, they make cementitious self-leveling products for that. You would typically need to do moisture testing of the concrete prior to doing anything else and this testing should meet the requirements of the leveling product and final flooring product you are installing. Since I am going to assume that you will still need to “level off” I would recommend that you look at Ardex and Mapei in your area. They will have leveling and moisture mitigation products. Good luck.

  15. Pete says:

    Thanks for the great article. I recently bought a 1989 California single story 1400sf home on a slab in Paso Robles, California. We hired a concrete polishing company to come polish and seal the concrete floors of the kitchen and living room just because we thought it would be easy maintenance and a nice touch. They won’t be out to do it for a few weeks at least, but while I was cleaning up I found three small wet spots in the middle of the kitchen that had obviously come up from below somehow. They are only a few inches in diameter and are sunken a little bit and seem like maybe they’ve been recurring for awhile. The old owner had a vinyl sheet floor in that room that I tore out. I’m in the process of trying to determine whether those spots are from ground water that has somehow found it’s way down there or from a drain pipe leak. We had some good rain but it was about 2-3 weeks ago. The previous owner was also saturating the lawn and garden beds daily though before I realized it and shut it all down over a month ago. Maybe contributing to a high water table? We started a water diversion project to dig french drains and grade the yard and garden beds properly. I’m now also wondering if there was even a vapor barrier installed in the first place. I haven’t found someone to do an RH test on the slab yet but I was able to do an MVER and got the following results:
    Living room: 3.53lbs MVER
    Hallway: 4.40lbs MVER
    Kitchen: 8.68lbs MVER
    Entryway: 5.38lbs MVER
    Other than the raised MVER in the kitchen from that issue, are those numbers pretty normal for everywhere else or would you suspect tis home doesn’t have a vapor barrier? How do I find someone to do a Rapid RH and would it give us a lot more info to work with? Unless we determine we have to sawcut the concrete in the kitchen due to a drain leak, would it still be okay to have the polishing company grind, polish and seal it? Would that stop the water wicking up there too until we get everything solved and dried out or am I asking for more problems? The plan was to put ceramic tile in the bathrooms, polished concrete in the kitchen and living room, and some kind of floating wood floor everywhere else. So that also brings up the question would I be okay with a standard moisture barrier with taped seems or would I be better of finding a DryLok type roll on waterproof coating for those areas?
    Thanks, sorry for all the questions …and keep up the good work!

    • Jason Spangler says:


      Thanks for the questions. There are a lot of them and I am going to hit the main ones. I would guess, based on the age of the home, that there is no vapor barrier. Those MVER numbers, if the tests were done appropriately, don’t seem too out of line. I would make sure you discuss your concerns with any and all of the floor finish professionals that you will be contracting with to complete the various aspects of this job. I would suspect that the polishing and sealing process will be breathable enough as to not cause major problems. You may still get moisture and depending on the situation, there can be some salt-like residue that may reach the surface. With the tile, they may use a crack isolation membrane that also helps dissipate minor amounts of moisture. Good luck.

  16. Jed McGuire says:

    Previous owners laid ceramic tile on basement floor. They butted it up to existing base/trim and put 1/4 round down to cover gap. When we went to remove the base so we could carpet over the tile we noticed some spots of mold growing behind the base. We are assuming that is because the concrete couldn’t “breath.” We surface treated any potential mold and want to prevent the issue from progressing. An idea we had was to hammer drill holes in the grout to the cement throughout the entire basement so that it can breath. Do you think it would help and is it worth the time and effort. Obviously if it allows moisture to escape it would be worth it, but wondering if anyone has done anything like this.

    • Jason Spangler says:


      Thanks for the questions. I can’t say I have ever heard of anyone doing this before. In general, grout lines tend to be somewhat breathable for moisture vapor, so depending on the grout line width and size of the actual tile, things MAY be breathing more than you think. Since the mold seems to be behind the base trim, I wonder if it is from the wall and not the floor. Something to think about. Good luck.

  17. Toni Oswalt says:


    Thank you for the great article. I have been discussing some moisture issues with my flooring installer and structural engineer and hope you can provide some more guidance/suggestions. Our home was built in 2003 and we purchased in 2011. We have dealt with multiple moisture issues and have at this point installed a French drain, dry river bed, built a berm, torn out the berm and installed a huge ditch in our yard to run water off. To explain our house was built midway on a hill and the back slab was dug down into the ground so the entryways are level with the ground. It appears we have stopped ground water from entering the house but are now dealing with a high moisture slab. We discovered this after installing a commercial grade floating LVP floor throughout the entire house, there was no visqueen installed under the floor. The flooring is now cupping in multiple areas and when lifted there was standing water, we have ruled out any other source at this point other than condensation build up from the slab. Our engineer suggested sealing the floor with a product such as bone dry before installing a new floor. Our installer is hesitant about this because he is concerned that the moisture in the slab will move to the sill plates and start rotting those. Any suggestions on how to proceed would be greatly appreciated.

  18. Access Doors and Panels says:

    Wow, this is a fantastic post! Water on the floor must be drained before the rest of the cleaning process can begin. Cheers

  19. Hannah says:

    Hi thanks for all this great info! I have a living room that is on slab – polished concrete with radiant flooring in it. In the summer and (and spring and fall) it’s a disaster — when air from outside hits it, it condenses, and then we have trouble with any wood (bookcases etc.) that sit on floor. We use rugs which helps a little but not a lot. We want to cover the slab with wood flooring. I know we will need to put a moisture barrier down before laying the floor (and we will give up the radiant) but I am wondering, given the slab mass, whether this is really enough? do you think we need to insulate under the wood floor as well? and any thoughts on how we can track the mositure over time – and once the wood floor is down? We’d like to put down real wood but are considering engineered simply to be better protected if dampness is an issue….any thoughts appreciated! Thanks!

  20. Ronald Raver says:

    Hi Jason. My home was built in 1976 (tract home). In March 2015 (?) we replaced carpeting and ceramic tile with interlocking vinyl. Slab was leveled in places. Over time, vinyl started buckling. Vendor agreed to replace in November2020 and when removing flooring moisture was very present. New flooring they placed vinyl sheeting as a vapor barrier. Briefly, more buckling. Surface indicated with meter/tester low or no moisture. Removing one of the planks and lots of moisture indicated. I do not have any water leaks; a structural engineer says my slab is OK; I had a plumber test my sewer line. So, what’s causing the moisture? Needless to say, both floors prior to install were bone dry. I live in San Antonio area and we’ve been under drought conditions so not a lot of rainfall.

  21. Mia Lynn Shaffer says:

    Hi Jason,

    My house was built in 1971. On September 16 of this year, I had my family room slab mudjacked because there was a 1.5″ slope at one corner. Three days later I placed some items from my garage on that floor because I had my garage floor and driveway replaced the following day. Today I moved the items back to the garage, only to notice that the boxes were wet on the bottom and the concrete floor has damp circles around most of the filled mudjacking drill holes. When I first placed the items there, the floor was bone dry. I have lived in the house for 14 years, and have never before had any water or moisture in that room. I am schedule to have a new engineered wood floor installed in this room in five days.

    What do you think could be causing this to happen? What is the remedy?

    Thank you!

    • Jason Spangler says:


      Thanks for the email. It sounds like there is either moisture from the material put in the holes or moisture coming up from below through the material in the holes. I would ensure you communicate this issue to the flooring installer so they might address it with a topically applied moisture retarder or better adhesive. Good luck.

  22. Jesse Grifka says:

    Hi great article! I live in Houston and am remodeling a 1970s slab on grade. The ceramic tile is being replaced with reclaimed brick set in thinset. What recommendations do you have on any kind of sealer/barrier that I should consider installing before installing the bricks to prevent efflorescence? Thanks!

    • Jason Spangler says:


      Thanks for the question. I would actually defer to either the contractor installing the brick or I would consult a concrete sundry reseller in your area. Good luck.

  23. Peter veltman says:

    Hi Jason, thank you for you’re time. It is a floating LVP floor from the Home Depot.I removed an existing floating Laminate floor and found that adhered to the slab was a layer of the old rubber pad from a previous install. I did not want to scrape it up and painted a layer of Kilz antibacterial paint over it. I did not do a moisture test as I believed that with the combination of the old rubber pad and the Kilz it would act as a moisture barrier. I bought a dehumidifier on the 27th and have it running continuously @40. I am emptying the 25 pint collection bucket every 12 to 16 hours. I am in the process of removing the flooring and saving what I can. I will have someone come in and scrape the floor to bare concrete and then do a moisture test. I obviously need to figure out if I do reinstall the LVP this problem of water collecting under the flooring. I hope you or someone with a similar problem can help out.
    Best Regards, Peter.

    • Jason Spangler says:


      Thanks for the reply. I would say that once you get the moisture testing results, this will help you better understand what needs to be done to install the floor. Good luck.

  24. Peter Veltman says:

    Hello Jason, I bought a 1100 sq.ft. Villa in N Ft Myers Fl. In January of this year and had a new air conditioning unit installed with a Remy Halo air purifier on March 5th. The owner/installer suggested we run the unit full time even without air conditioning because it would help with my COPD. I installed vinyl plank flooring from HD on March 13th in the 400 sq ft living room. There are two sliding glass doors that go out to the lanai and an entry door to the kitchen. For 6 weeks I worked on the place frequently going in and out to saw in the lanai. About 2 weeks ago I noticed dirt collecting in the seams of the flooring which I cleaned up with a wet rag. We moved in last week and the seams started to collect dirt in more places than before and as I was cleaning a seam I pressed down and liquid seeped up and onto the flooring. I subsequently removed a couple of planks and there was and is standing water on the concrete floor which I had sealed w Kilz prior to the install. So my question after reading you’re other answers, is it possible for this moisture collecting under the flooring to be caused by running the ac unit continuously and if so how can that be mitigated.
    Thank you for listening.
    Regards, Peter Veltman

    • Jason Spangler says:


      Thanks for the question. You offered up a lot of good details, but I still have a few questions:

      1) Is this a floating floor or adhered floor?
      2) Did you do moisture testing on the concrete slab prior to installing the floor?
      a. If so, what were the results? Are these in line with the manufacturer’s recommendations?
      b. If not, did the manufacturer recommend doing so?
      3) Were there any recommendations in the manufacturer’s installation instructions regarding the placement of a vapor retarder on top of the concrete?

      To simply answer your question, the constant running of the AC COULD be causing condensation on the top of the slab, depending on how cool the surface of the concrete is compared to the dew point of the air, but this may not be any part of, or the entire cause of, the problem.

  25. Kenneth Pitzer says:

    Dear Jason,

    We have a similar moisture issue as the previous post from Justin Lee on December 5, 2017 at 7:01 pm.
    We request your recommended tile installation procedure for moist slabs.
    The backstory is, we live in Orlando, Florida and know we have a high moisture area under the concrete slab and we’ve tried to find out the source. I’m wondering if we have a spring or a brook under our home. We live with a pond behind our home, but the moisture problem is near the front of our house about 10 feet away from the outside wall. The pond is approximately 40 feet behind our house with the water level about 3 feet below our slab. Our home was built in 1991 and we are the original owners. We became aware of the moisture issue in 2016 a year after we had new engineered wood floors installed to replace carpet and tile. However, the area with the wood floor problem used to have porcelain with no issue. We began having issues with the wood surface bubbling and discoloring. That led to us also discovering moisture damage under the carpet in the bedroom adjacent to the wood floor damage and damage to the nearby bathroom cabinet which was installed directly on the slab. We have ruled out any water leaks. Prior to the remodel we had the whole house re-piped with piping in the attic. After discovering the wood floor issue, we hired a leak detector who said there was no leak and it could be moisture leaking through the slab as we did have one side of the house where the ground was continually wet. Even then, we were not convinced that was the issue because the moisture issue was not around the edges of the rooms/house, so we hired two separate companies who scoped the drain pipes under the house to check for damage/leaks. Again, no leaks. We first added gutters and last spring had french drains installed on both sides of our home. We now have a dry yard, however, we do still have high moisture in the same areas inside. We also have many efflorescence areas forming on top of the slab in our garage.
    We have an easement on what was the “dry side” of the house that has an underground drain pipe running from the pond between our home and our neighbor’s home and empties into the woods behind the homes across the street. The county said there is no possibility of leaky pipes/drains on their end.

    All this to say, we want to replace the floor with no worries of future moisture issues. We plan on replacing the wood with tile, however, have read of many water issues with tile also. Our biggest question now is, do we seal the concrete slab in the home before installing tile? We’ve heard two different opinions on this… most installers say to seal the floor before installing a new floor. A certified wood flooring inspector said to replace with ceramic tile (instead of porcelain) and use hybrid epoxy grout (as wide as the tile manufacturer recommends) so the floor will breathe. So far, we haven’t had any standing water, just high moisture. We are thinking of sealing the floor first, however, could we be dealing with a hydrostatic pressure issue under the house in the future? We would be most grateful for your help and advice. There was no solution posted to Justin Lee’s post on December 2017.

    • Jason Spangler says:


      Thanks for the question and detail. Based on your explanation, it sounds as if you may not have an intact vapor retarder so moisture is able to get from the soil to the bottom of the slab. Since you have taken many positive steps with regards to water drainage and ruling out water leaks, I would say your best plan of attack for this would be some type of moisture mitigation product applied to the surface of the concrete prior to installing the finish. If you are going back with tile, you may also want to investigate some type of uncoupling membrane. As far as hydrostatic pressure, this is pretty uncommon and will usually only be found in basement-like settings where the slab is at a level below the actual grade and water table. Good luck.

  26. Mohsin Kabir says:

    I am really shocked to see you, Jason. You guys are given a reply to each and every comment. I really appreciate your time and thoughts on this.

    • Jason Spangler says:

      Thanks, Mohsin.

      We TRY to answer them all. Our philosophy is if someone spends their time submitting a question, we should do our best to respond.

      Take care.

  27. Luciane Maimone says:

    Dear Jason,
    Thank you for such a detailed explanation about the concrete part. I have a question about best practices installing a tongue and groove flooring over a cement patio. We have paid a builder to do that, but he cannot figure out a way to avoid the wood to bow up. The slab was done several months ago, so I’m assuming it had time to dry. Before doing something more drastic I’m trying to find information about what the proper techniques are. Can the wood be in contact with the cement or should we use raisers? What kind of flooring is adequate in this case (thickness or wood we should avoid). Should we use a polyethylene barrier or something similar? Should there be a scape route (that’s as technical as I can be, lol), for example to let the water that condensates evaporate? It’s been really hard to find information. I can mostly find instructions for indoor flooring or the regular deck floor (not tongue and groove). I appreciate your help!

    • Jason Spangler says:


      Thank you for the questions. I believe your best bet would be to reach out to the National Wood Flooring Association at They have resources specific to your needs and the ability to give you some guidance. Good luck.

  28. johnbosco says:

    Great work

  29. William Ian Wightman says:


    I own a ground floor condo. directly below our unit is the underground parking lot.

    Our floor is concrete and the concrete ceiling in the parking directly below us is insulated with spray on insulation that looks like dirty cotton wool. The garage is not heated and the large access door is gate.

    we recently installed vinyl flooring that locks together with tongue and groove.

    The vinyl is now cupping and creating a trip hazard.

    The flooring company has returned and lifted some of the flooring and discovered moisture on the concrete. once the flooring has been lifted off the moisture content drops to an acceptable level. I guess it just evaporated.

    any suggestions in relation to a fix.


  30. John Ragland says:

    Hi I just bought a house and find that a bathroom cabinet build up humidity in the lower cab with mildew smell. My plumber pulled the wall and bottom out and immediately his glasses.and mirror fogged up. We found that the bathroom is raised above the slab, two 2x4s laid sideways frame the bathroom. Then a thick solid plywood (i guess). He cut into wall sheet rock and there was already an 6×6 cut into plywood below bottom cab to expose some pipes.
    Plumber didn’t find any leaks but said there is a lot of humidity down there. Called a foundation company and the person said not enough crawl space for the to come out. Now I’m trying to figure out what to do.

    • Jason Spangler says:


      Thanks for the questions and sorry for your issues. I’m not sure I have a solution for this given the limited access. It sounds like there may be moisture coming through the slab if there isn’t any evidence of leaks. Being trapped and without much, if any, ventilation it may continue to have a high level of humidity. It may be best to consult a general contractor and see what ideas they may have to remedy the situation. Good luck.

  31. Leslie says:

    I have lightweight on the top floor. Water was accidently spilled on it. We have in floor heat on and it slowly drying. Very slowly. Any advice?

    • Jason Spangler says:


      Thanks for the question. I would say to continue doing what you are doing if it is drying out. It does take time depending on the amount of water spilled. Another thing to pay attention to is the relative humidity in the air. You want to make sure to maintain a low level of humidity in the air to ensure continued drying. Good luck.

  32. Kailash says:

    Hi Jason,

    I have wooden floor at ground floor and it is backed up below with sponge foil which is overlayed over concrete floor. After 6 mts of installation the wooden floor was turning black and we removed wooden floor. We see moisture content on concrete floor. So pls suggest what to do to get rid of this moisture content which is spoiling wooden floor.

  33. Lynda R. says:

    Hi Jason, you are so knowledgeable. I hope you can help me.
    We live in Quebec, Canada. We purchased a country home that has very high humidity in the basement and there is a very strong musty smell. There is a sub floor over the concret and a carpet glued to the subfloor. We plan to remove the carpet and put down insulated vinyl planks that click together. My question is, because the humidity is so high and the smell is quite strong, will putting a vapour barrier down on the subfloor, before installing the vinyl flooring, be a good idea? And will it help to eliminate the humidity and smell? Thanks for your help.

    • Jason Spangler says:


      Thanks for the question. First thing I would recommend is determining why it is so humid down there. Is it moisture in the concrete, lack of ventilation, water intrusion in a wall, etc. Vapor retarder on top of the slab may help, but I am not sure it will eliminate the issue you describe. It may require additional things such as dehumidifiers and ventilation. Good luck.

  34. Irene Gibson says:

    Hi Jason

    I live in Bedfordshire UK and had Karndean laid in my hallway dining room and kitchen when I moved in 9 years ago. I noticed after a couple of years that tiles were lifting and that I had damp tide marks going up about 2 inches or so from the skirting of my hall walls and also my lounge wall ( which comes off directly from the hall but is carpeted.

    A leak was found from piping between the hall and dining room radiator – this was sorted by capping off the pipe and putting the pipe worj through the hall. The damage resulted in my having to have the Karndean taken up, the area allowed to dry for a while and then new Karndean being relaid.

    It is now happening again. Although the lifting of tiles has not been nearly as extensive as the last time and this very close to the place where the pipe had leaked origanally. I have tide marks going up my walls again though.

    My question is is it possible that the floor was not completely dry before relaying the tiles or am I likely to have a problem with my concrete floor? and if this is the case can I sort out a small area around the damage or do all the tiles have to come up again. Grateful for any advice.
    Thank you.

    • Jason Spangler says:


      Thank you for the question(s) and sorry for the issues. It is possible that the concrete wasn’t completely dried out, but I would have expected if that were the case it would have shown problems to the floor much sooner than years down the road. In the US it is very common to do “repairs” and not complete replacements if it is deemed reasonable by the fitter. Good luck.

  35. Sunny D says:

    Hello Jason
    I live in Tampa Florida in a 2nd floor (top floor) condo. For the past 3 weeks I have been noticing sweating from my flooring – luxury vinyl planks installed less than a year ago. The planks have an attached foam layer in addition to underlayment placed on the concrete slab. Two areas of the floor near the kitchen were cold in temperature and little speckles of water was felt on it. A plumber came to inspect for leaks, none found. The flooring company came out, they removed flooring from sections that were sweating but no overt leaks found. There was however sweating on top the underlayment that rested on the concrete floor but under the underlayment was not wet but had very cold concrete, much colder than other areas of the floor. The HOA had a water leak company come out today to test all my plumbing and water sources but no leak was found . They used a infrared red device that showed dark blue spots in the 2 areas of my flooring that were sweating but did not determine the source of why those areas of the concrete slab was cold or what was causing the sweating. They think it maybe condensation from the AC unit from my neighbor below or some sort of plumbing issue from below. No were else in the condo has this issue or picked up any cold spots on the infrared red device.

    Do you have any thoughts as to what my be the source of my problem?

    Thank You

    Sunny D

    • Jason Spangler says:


      Thanks for the question. I would agree that there would seem to be something like the AC duct work not sealed well, or something along those lines, in the unit below, causing these isolated cold spots. I would lean towards condensation based on where you are located and what little information I have. Good luck.

  36. Jerry Reniak says:

    Hello Jason,
    I have recently started remodeling a house that was build in 1950. It is on a slab.
    To level out the slab I placed a 6 mil moisture barrier, green 2×4, 1 inch foam insulation between sleepers, then ¾ TG plywood. That was about a month ago but the other day I had to run a wire and pulled up one of the pieces of plywood. To my surprise I found water puddles under plywood and insulation. The water is collecting on top of the moisture barrier but the underside of the plywood is dry to the touch. I found water not only under the plywood in this room but also in different rooms on the first floor as I was trying to diagnose if this was a water leak and where it could be coming from.

    I live in NJ and for the last 3 weeks we have had 80-90 degree weather and intense humidity. Since the house is still under construction with no A/C my suspicion is that this is condensation but I am shocked at the amount of water that has collected. Can you provide your thoughts? Is it likely this is condensation or is there another possibility?

    • Jason Spangler says:

      Thanks for the question. It could be condensation or dew point. One way to determine this would be to measure the surface temperature of the area(s) in question with an infrared thermometer. Then measure the relative humidity and temperature of the air. Once you have the RH% and temperature of the air, plug the information into this calculator This will give you a dew point temperature that you can compare to the information you obtained from the infrared thermometer. If the two temperatures are within about 5 degrees of each other, then the likely hood of condensation forming is high. Personally, especially if you are going to be installing the finished floor product down, I would want to know the internal relative humidity of the slab. My guess, being new construction, the level of moisture (RH%) in the slab is also very high. Good luck.

  37. Nicole Ferranti says:

    I recently discovered a mold issue in my house and handled it by replacing my HVAC unit,treating the HVAC handler closet, replaced and cleaned the duct work and gutted and entire bathroom. I thought the issue was resolved. However last night after several days of rain (i live in florida) i realized the odor i was smelling prior to replacing the HVAC unit was back. it always seems more pronounced after wet weather. it does not seem to be coming FROM the AC unit but definitely gets moved throughout the house when the AC kicks on. I have noticed that the people who owned the house before me placed laminate flooring on top of parquet flooring and that several areas in the main living area (where the odor is most pronounced, i have had to fix some buckling due to the old parquet pi rising up. it does appear there may be some moisture related issues under the laminate flooring. I am on a concrete slab foundation. I am looking for suggestions on how to either test my theory that this is where the odor and moisture issue is coming from and some possible solutions to remedy the issue

    • Jason Spangler says:

      Thanks for the question. I would look to possibly bring out a flooring inspector to evaluate the areas where you have had issues. You may want to start here Doing this would probably at least tell you that the issues are potentially related to moisture in the slab. At that point, you may be looking at replacing the floor, after using a moisture retarder on the surface of the concrete. Good luck.

  38. Kipha says:

    We are putting down a floating laminate floor and my husband is the type of person who likes to be super careful about everything. As a result we are going to lay down a plastic vapor barrier on top of the slab PLUS put pergo gold underlayment on top of it, THEN finally the flooring. But we are worried about getting moisture between the plastic sheeting and the underlay. So as a solution, what if we take the plastic moisture barrier up the wall a couple inches, but then end the pergo gold about an inch from the wall and tape down the pergo gold to the moisture barrier with some kind of waterproof tape around edges? Won’t this tape seal make sure nothing can get between the underlay and the plastic moisture barrier? If this is a viable idea, is packing tape a good tape to use? The so called underlayment seal tapes seem like a gimmick.

    • Jason Spangler says:

      Thanks for the questions. Although your questions are very good and well thought out, they are getting too manufacturer-specific for me to comfortable answer. Pergo should have a technical hot line that you can call to get the information you desire. Good luck.

  39. Installing epoxy says:

    Its not so easy to maintain the moisture for flooring slab works. i hope this post will help a lot . No one would like to face flooring issues just because of moisture porblem! thank you for sharing your post

  40. Levi says:

    Hi Jason, I read the whole conversation between you and Lisa, I had the same issue as she talking about. I got some informative answers from you. Thanks a lot for your article and some brilliant answers.

  41. Art says:

    Much appreciated Jason. It makes sense. Thanks again.

  42. Art says:

    I am a first owner of a house that was built in 2016 and live in Northern Colorado. In our unfinished area a few years back we sealed our floors with a product that is used to seal garage floors (the stuff with flakes). I have noticed recently while either moving storage bins around as well as some work out machine mats, there is condensation occurring under those areas only, meaning I do not have any water present where the floors are exposed. Its also not present under every bin for example.

    Do you have any idea what could cause this condensation? I suspect lack of air circulation in conjunction with humidity(don’t have that issue in Co), coldness of the floors in the basement, etc.

    FYI – I have a sump pump in the basement, but its bone dry and have never had landscaping or drainage issues.

    Any insight to the problem and/or recommendations to solve would be appreciated!

    Thanks and take care.

    • Jason Spangler says:


      Thanks for the question. If I were to wager, the condensation is appearing when you put something on top of the floor that lessens the concretes ability to “breathe” and therefore the moisture that would normally just escape into the environment, unnoticed, is being collected under the mats/bins. If this is the case, about the only easy solution I am aware of is to elevate whatever is in contact with floor to allow airflow. You may also try a test area the way it is, but with airflow across the surface. This MAY lessen the issue. Good luck.

  43. Violeta says:

    Thanks Jason for your answer and help.

  44. Violeta says:

    Hello, my house is build 2014. I am the first owner. In february 2019 we replaced the the toilet bowl but we replaced it by ourselves following the instructions of the toilet bowel manufacturer. So we installed the toilet bowl in February 2019 and a year later in February 2020 the laminate floor around the toilet bowl began to swell. Probably we did not install the toilet bowl correctly so water was leaking under the laminate floor, there was no water or moist on the surface of the laminate. We stopped using that washroom completely, and after three months the swelling of the laminate disappeared almost completely. Three days ago a professional came to install the toilet bowl correctly and he said that there is moist under the laminate, the laminate is still wet. He said that even if he installs the toilet bowl perfectly the laminate floor will swell again because the water will leak again into the laminate. He said that we should first call a service to dry the laminate and under it. I called a service and they said to dry the layer below the laminate will cost thousands of dollars, that the laminate will be taken away and after drying the area a new laminate will be put in the washroom.And the whole washroom is about 1,5 square meters.I need your advice if there is another solution for the problem, We replaced two more toilet bowls by ourselves couple of months later and now I am scared if water is leaking under these two toilet bowls too. How to check if water is leaking under the other two toilet bowls?

    Thank you

    • Jason Spangler says:


      Thanks for the questions. First, even if the laminate is wet underneath, I am not sure how that would make a perfectly installed toilet bowl still leak? Is it because the laminate is currently swollen and the original problem hasn’t “disappeared almost completely” as you state? Thousands to replace this, if my calculations are correct, very small washroom floor, seems excessively high, but I am not familiar with your local market. I would shop around and see if you can get a better price on this. If not, you may want to have someone remover the floor, leave the floor off to dry the subfloor naturally, and then have a new floor installed. Lastly, if you have any question about the other two toilets, I would recommend just having them changed professionally to ensure their isn’t an issue.

  45. Lisa says:


    We are building a new house in a subdivision by a nationally known builder in Ft. Worth, TX. The shell is completed: all brick (one story), drywall, windows, roof cabinets and doors. Saturday it rained all day. We checked the house out Saturday evening, to check for leaks in the ceiling. We did not see any wet spots. I went by tonight, Monday at 8:00 PM. I now see moisture on the concrete foundation, at the base of several interior walls. I am quite concerned, because we purchased a log home in OH with a basement that flooded about 8 times, before we realized the water was coming up through the concrete floor. We had to have two sump pumps installed to fix that issue. We do not want another flooded home or issues with new flooring that will be put down in the next 4-6 weeks. I would like to understand if this is an issue, before talking to our field manager.


    • Jason Spangler says:


      Congratulations on the new house. My guess is that it isn’t an issue, but I would still bring it up to your field person and have them explain to you what it was or may be. You may be looking at an issue with how the rain came down or collected externally due to the unfinished grading you typically see with a house under construction. Good luck.

  46. Tisha says:

    I live in Ottawa, Canada in a house that was built in 1978. 3 years ago we removed the original flooring in the basement. We had a combination of peel and stick tiles, carpet and sheet vinyl. We then laid luxury vinyl plank flooring, the kind you just drop into place and we used double sided tape on the perimeter and key areas. After a year I noticed that some planks were lifting and there is efflorescence underneath. Our flooring company has not been helpful, just confirmed that it was efflorescence. How do we deal with this problem. There were no signs of this when we took up the old floor. Thanks for your help.

    • Jason Spangler says:


      Thanks for the question and sorry for your current flooring issues. Efflorescence typically can’t happen without there being moisture in the concrete to help transport the salts to the surface. Being the house is built in the late 70’s, there may be a good chance that it either didn’t have a vapor retarder under the concrete slab originally or that retarder is no longer whole due to age. Either way, this COULD be where the moisture is coming from to move the salts to the surface. Depending on the glue and/or the breathability of the flooring product originally installed, this moisture/salt may not have been a real issue so you may have never noticed it. I would search here for a flooring inspector and have them come out and evaluate your situation specifically. Good luck.

  47. sal says:


    I’m in southeast Florida, we removed carpet and installed porcelain tile on our slab (20+ year old home)
    now dealing with water and mineral deposits on some grout lines.

    had no idea this would happen, it’s only a few spots but we would like to sell the property at some point.
    is there any suggestions.

    thank you

    • Jason Spangler says:


      Thanks for the question. This could potentially be problem related to moisture in the concrete. Older slabs of this type probably don’t have an intact vapor retarder below the slab so moisture is able it get into the slab from the soil below. Having a breathable carpet originally, you may not have noticed anything. Now that you have a fairly non porous product installed it is finding its way through the grout. Have a discussion with a reputable tile shop in your area and see if they handle or know of a grout that may be less susceptible to this type of issue. Good luck.

  48. Hello Jason
    I have an attached 3-season porch with a concrete slab installed in 1956, tiled in 1995. It is always dry except when the Spring/Summer/Fall ambient air dew point and floor temperatures meet and the water vapor turns to water and drops on the floor. I live in Central Minnesota with moderate to minus 20 or colder Winters, and typically dry air. So I think the problem really is a 3-season one. We live on a large lake and porch is about 45 feet from waters edge. Ground water under porch is usually down about 3 to 4 and lake level is controlled by US Corp of Engineers. I want to put down a floating Luxury Vinyl floor and have several concerns. I know the floor will still get wet when the dew point is the right temperature, but I think the interlocking planks are tight enough so water does not leak through, or we will use some silicone sealer in the locks when we lay the vinyl planks. However, I am also concerned about the area between the vinyl and slab. In the 30 years we have lived here I never say any water coming up through the slab, but, would there be condensation between vinyl and slab? If so, the vinyl backing would get wet and lead to mold, and that could be a big problem. If my concern turns out to be reality, I have thought about laying down a vapor barrier, laying 1X2 or 1X3 inch furling boards on the barrier at proper intervals, and attach 1/2/ inch plywood, and lay the vinyl planks. There will be an airspace under the plywood so the floor temperature should then approximate the ambient air temperature which may then eliminate the dew point problem. I will appreciate your comments and suggestions.
    Gene Jaster

    • Jason Spangler says:


      Thanks for the question. In general, your floor structure design sounds valid if there isn’t moisture also coming up through the slab. If there is, furring strips might not be the best long term option. Given the age, I am going to wager that there isn’t a vapor retarder under the slab so moisture has access to the bottom of the slab from the soil. Now, that doesn’t mean you don’t also have a separate dew point issue. You may want to look at a product called Dricore. Now I don’t usually put name brands in here and I am in no way recommending this because I have no first hand knowledge of this product. It is just when you started explaining your idea of how to solve the problem, I thought about this product because it seems to do what you were trying to achieve. I would consult the vinyl floor manufacturer for compatibility prior to purchasing. Good luck.

  49. Jason Kivo says:

    Hi Jason,

    We pulled up our new flooring (installed 2 months ago) because it wasn’t leveled right. We had engineered wood and now waterproof vinyl. Under the waterproof vinyl we noticed small amounts of pooling waters in the small slab cracks that we have. Since we removed the vinyl flooring the water hasn’t come back. Dry as a bone as they say! I am wondering if this water is condensation from the humidity from our excessive air conditioning. We tried to blast water into our home from outside to see if that was the source but couldn’t make it happen. The water pooling was evenly found throughout the floor area. This tells me its probably that. I have a photo I wish I could post here. Anyway, do you have any thoughts on this? recommendations? I have concrete slab and flooring no vapor barrier.


    • Jason Spangler says:


      Thanks for the question. I would think that if it was only related to the excessive air conditioning then the floor would still show signs of condensation, even without the flooring installed. It sounds like there may be excessive moisture in the concrete that, when the floor is installed, condenses on the surface because it can’t escape into the air due to the low permeable vinyl that is installed. Checking the moisture level in the concrete and also looking at relative humidity and temperature in the air vs the dew point would be the first things I would look at. Good luck.

  50. Regan says:

    Thank you Jason. I really appreciate your time and thoughts on this. What specific moisture tests would you have performed and what type of company performs them?

  51. Regan says:

    Hi Jason,
    I recently purchased a home built in 1984. The house had 6 year old carpet through out the home until the seller installed porcelain plank tiles (5/2019) everywhere except the bedrooms, which had carpet and the bathrooms which were previously tiled (no issues are noticed in either bathroom). We noticed efflorescence coming up through the grout lines in the newly installed tile. We had leak detection come out and determined that all of the windows were letting water in that dripped down on the slab almost immediately from spraying with a hose but found no other signs of a leak. We also had a moisture meter test and no one said that they detected moisture under the tile. We then pulled out all of the carpet in the bedrooms and all of the pads had moisture/water damage. We have since sealed the windows. The efflorescence is the worst in the front living room (which has a large window and is adjacent to the worst of the bedrooms with a moisture issue from a leaking window). Since we ripped up the carpet and let the slab dry out in the bedrooms, we have noticed that the efflorescence isn’t as bad in adjoining tiled areas but there are about 3 spots on the floor in the living room that a little bit of water is pooling in the grout lines. We would like to continue to install the tile in the three bedrooms. Our tile installer said he would scratch out the grout and replace with a better grout for sealing as well as roll down a moisture barrier before he installs the new bedroom tile. He is also going to pop out a couple of tiles in the living room to see what is going on in regards to the water pooling. Is it possible that water/moisture was trapped on the slab during install from the leaking windows? We don’t want to have this issue in the bedrooms as well. We live in Florida and it rained everyday during the summer, which is when this issue was noticed. I look forward to your advice. Thank you.

    • Jason Spangler says:


      Thanks for the question. First, I haven’t heard that there was any REAL moisture testing done on the concrete after the flooring was removed. My recommendation would be to do proper moisture testing of the entire slab and then make a determination about the types of products to use to remedy the issue. The recommendations by the flooring installer don’t sound out of line at all. Good luck.


  52. krista hilmen says:

    Hi Jason,
    We purchased our home in 2009 with basic flooring installed. In 2013 we replaced the downstairs area with laminate flooring. Over the years the flooring began to buckle and bubble. We pulled the floor up in November 2018 to find that the entire 1500 sf needed to be removed. The moisture barrier was soaking wet (as well as having mold build up). No one has been able to determine a leak or where the water is coming from. We have called in the builder and they told us that they would have sealed the floors had we “upgraded” the flooring with them. So we ordered a sealer online, sealed a portion of the floor (twice), waited 72 hours and then laid down sample vinyl planks on top of it. Within two days the floor was wet again under the sealed area. At this point we are not sure what to do. Is there a someone we could call to advise us? Do you have any recommendations going forward? At this point we really want to get floors installed but the continuous moisture is a problem.

    Thanks so much,

    • Jason Spangler says:


      Thanks for the question. Typically a proper “sealer” isn’t a DIY job. There are different degrees of “sealing” and you really need to understand how much moisture there is in the slab before you can attempt to remedy. I would look for a reputable flooring installer that will perform moisture tests on the concrete and then provide you recommendations for a successful installation. Good luck.


  53. rosie says:


    I purchased a home that was remodeled in 2015. I’ve been in the home for 2 years. I have recently noticed a mildew smell in the bathroom. There are no signs of mildew on the walls but I am noticing the floor in the bathroom (ceramic Tiles) are moist and the flooring in the hallway near the bathroom is weltering or bubbling up ( floor is laminate wood flooring) What could be causing this and what and who should I Call? My home was build on concrete slab

  54. Andre Rosinski says:

    Hello Jason,

    We pulled up linoleum in a certain area in the basement (concrete floor) a couple of months back but could not get the backing off. I will take care of that soon but my question is since we bought the home with pet problems (regrettably) our painter sprayed the entire basement with Bin Zinnser including the linoleum backing 3 months ago. The smell from the Zinsser took a while to go away in the rest of the basement (all drywall and bare concrete floors) but the part where the linoleum backing is stinks just like at day one. I assume that the Zinsser is somehow trapped between the concrete and the backing, is that a reasonable assumption? Once we get rid of the backing do you suggest to treat or clean the floor somehow?

    Also, the rest of the basement seems to still have a slight smell of the sealer, I think it is coming from the concrete floor. Would it make sense to paint it just like you would apply a top coat to drywall that has been sealed?

    • Jason Spangler says:


      Unfortunately, I have never used or dealt with Bin Zinnser, so I am out of my element giving you any advice in this situation. Good luck.

  55. Lucie says:

    Hi Jason,
    We had a new home built and moved in June of 2018. The engineered bamboo flooring as cupping when we moved in and buckled that November. Our windows had condensation and to where there was a puddle on my windowsills. We also have spray foam insulation, our air handler was oversized and running fast. When they slowed it down it seemed to help the condensation but the weather was also warming up at that time. We had all the flooring removed. The cement slab is still testing at a high level of moisture…32% Will we be able to have hand scraped engineered wood flooring? We have had 80 hours with the dehumidifier and blowers but still high moisture in the slab. We don’t know why it hasn’t been able to dry out.

    • Jason Spangler says:


      Thanks for the questions. Unfortunately, I am unaware of the concrete moisture scale you are referring to when you state 32%. The typically accepted concrete moisture testing methods for installing flooring are the calcium chloride test and the in situ relative humidity test. These give either lbs of vapor emission from the slab or an internal relative humidity. If the slab is truly wet, it would take more than 80 hours of dehumidification to dry it out. Your first step is to have a reliable concrete moisture test done. I would look here to see if there are any certified moisture testing people in your area. Good luck.

  56. Linda Childers says:

    We are looking at house to buy that was built in 1988. The hardwood floors have dark spots throughout the house and we think it is a moisture problem. Is there any way to test this without taking up the floors? We would like to know before we buy the house. We will put down all new floors if the problem can be resolved.
    The house is on a slab in Tampa .

    • Jason Spangler says:


      Thanks for the question. You may be able to discuss this with the home inspector prior to purchase or, if you are serious about the purchase, it may be worth having a wood flooring inspector come out and evaluate. You can find one in your area at

  57. Thank you for your valuable resources keep share the information like this…

  58. Alan Vena says:

    Thank you for your response Jason. I agree with your conclusions on my readings when measuring internally in the slab. As far as applying the Xypex product according to instructions, my first application was low on product for square yard. I was supposed to see results in approximately 30 days, but I still was reading high levels of moisture on the surface. I then took all the original product off the floor and did a more limited application carefully measuring pounds of product per square yard. In the mean time, 3 months had passed and the areas from my first application appeared surprisingly dry almost like the process took longer than it was supposed to. I was in contact with a factory rep during this whole process and they suggested that the product is not guaranteed if you have voids in a poorly mixed slab. I suppose my bottom line question is if I am not seeing moisture under my plastic sheeting after 72 hours, does that necessarily mean that the product has worked to the point where I could install tile? Is there any test that is best for my situation?

    • Jason Spangler says:


      The plastic sheet test isn’t really meant to be a “go, no-go” type of moisture test. It is more of an indication test. In your situation, it may be best to install a small test area and see how it stands up. Unfortunately, there isn’t going to be an absolute test method to confirm effectiveness of “sealing” products. Good luck.

  59. Alan Vena says:

    I live in Orlando Florida and own a home built in 1979. I bought the house in 1994 and the seller had had the house carpeted. I was not aware of any moisture problems with the slab until about 2009 when I installed laminate with a vapor barrier. After a few years I noticed the laminate was warping and when I ultimately pulled the laminate up the slab was sopping wet under the vapor barrier.
    I put in a french drain around most of the house sump pumps and it seems to be working especially during heavy rains. As I installed the drain, I determined that the water table is very high in our neighborhood.
    I used dehumidifiers to try to dry out the slab, but the results were not uniform and some areas still had an RH 2″ down at 99% and some areas were 25%.
    I was looking for another product to permanently seal the slab and tried a product called Xypex. After going through the process, which took a month, I still had areas with high moisture levels through the slab and others seemed to be reduced. The Rep thought it was a poorly mixed concrete slab. 3 months out, I am trying to determine if this product worked. I don’t want to install tile until I am sure the moisture transmission problem is resolved.
    My question is, what is the best way to do this? I have an RH meter that will read down to 2 inches, but during the Xypex process, they require you to super saturate your slab, so at the moment it is reading 99.9% moisture at that depth everywhere.
    On the surface, it is a different story. When I use a pin moisture meter, of course it will read low moisture, but I was not satisfied with that. I then put plastic sheeting down sealing the sheet down with tape for 3 days, and I am not seeing either the amount of moisture that I expected. Many areas show no moisture under the plastic. I was thinking about reading the surface with a pin meter immediately after removing the plastic and compare that with areas that have not been treated.
    Do you have any suggestions on how I can reliably determine if this slab is indeed repaired and ready for tile?
    Thank you for any information you can give me.

    • Jason Spangler says:


      Thanks for the questions. Most of the time when there is a “sealing” process being done on the slab for the purpose of diminishing moisture transmission, installers rely on the proper installation procedures and the claims of the product being used. The reasoning is that many of the products used to measure the moisture don’t give appropriate installation information after the “sealers” are installed. So the questions become, did you appropriately install the “sealer” you used, what claims does the manufacturer have in their installation documents (what is the maximum RH% the product will withstand and what does it claim to diminish the vapor transmission rate to). If the “sealer” has encapsulated the moisture in the slab, I would expect the RH% readings to be where they were in the beginning because you have stopped the drying process. In the same line of thought, the chemical make up of the product may skew the pin meter readings and the plastic sheet test may be showing nothing because the sealer is effective. This is one of the reasons why neither of these two types of testing methods are used in most flooring decisions, they can give very unclear results.

  60. Josh Handy says:

    Hello, we installed vinyl plank flooring directly on top of our concrete slab in the basement (the flooring is 100% water proof). A year later I noticed a section of the floor had moisture/water coming out of the cracks. I started to remove a section of the flooring and found there was a good amount of moisture/water under it. I am trying to determine the best way to fix this from happening. Is there a type of moisture barrier that should be installed before laying vinyl plank flooring on a concrete slab? Any recommendations on how to fix this issue with moisture occurring under vinyl plank flooring installed onto of a concrete slab? Thanks

    • Jason Spangler says:


      Thanks for the questions. Yes, there are products that can be installed prior to the flooring product to help with this problem. I would look for moisture mitigation products and a few of the bigger players in this space are:

      AC Tech

      Whatever you chose, just verify that it will work against hydrostatic pressure. This may be part, if not all, of the issue.


  61. Bobby Rogers says:

    Hi. I had my house retiled in Jan 2018. we did everywhere but the bathrooms and bedrooms. After approx 4 months i began noticing a white film in the grout line. This only happened in one room which we call our Florida room. I thought nothing of it at first and then i mopped the floors again and i would notice it again. I eventually got a grout scraper and scrapped for only about 2 mins and water shot up approx 10 inches high for about 5 seconds. After the pressure was released i was able to scrape out more grout. Water that smelled like vinegar continues to seep onto the floor over time. Now its been approx a year and we now have approx 10 different spots of that white chalk. I have had leak detectors out 3 times, numerous plumbers and even a scientist which my insurance company sent out. Nothing can be found leak wise. My insurance company has denied my claim so now I am at a loss as to who to contact or what my next step is. I live in So Fla and my house was built in 1967. Any advice would be greatly appreciated. Thanks
    Also, this only occurs in our Florida room. And its only started since we replaced the old flooring which was laminate and before that it was carpet.

    • Jason Spangler says:


      Thanks for the question. I can’t say I have heard a story like this related to tile. I have seen something of this nature on a sports floor. The white spots are probably efflorescence which is salts from the concrete that are transported to the surface via excess moisture. Looking at the age of the home and/or the potential that the sunroom may have been added later, if I had to guess, there probably isn’t an intact vapor retarder under that slab. This would allow moisture to migrate from the soil and into the slab. With the carpet that was originally installed, it would have been very breathable and you may have never noticed an issue. I can’t explain why you wouldn’t have seen it with the laminate. You may want to have a geotechnical engineer come out to investigate. Good luck.

  62. Robert says:

    We installed a laminate flooring in a bathroom that was part of renovation that finished Spring of last year. We got the flooring from Home Depot. (It had like a rubber layer at the bottom) We just notice some kind of residue coming from underneath one or two of the planks. The residue is coming between two planks and it it’s about 2′-0″ in length and the planks is between the curb of the walk-in shower and toilet. The contractor had put down this light blue paint like thing on the slab before he put down the flooring. Do habe an idea what is happening? What is the residue? and How do we fix the problem.

    • Jason Spangler says:


      Thanks for the question. I think first of all, since its under 12 months since the floor was installed (usually the warranty period) I would contact Home Depot and have them come out and evaluate the issue. I am wondering if it may be leakage from the shower or toilet or shower. Good luck.


  63. Michael says:

    Hello there, we live in Panama City FL where Hurricane Michael hit. We were a week from finishing our new home when wind driven rain flooded the house. Our master bath, closet, and laundry room are all tiles and had not been grouted yet. The moisture reading is 28 – 30%. The tiles are on concrete slab. How much moisture is normal in this situation? We were told up to 17% is acceptable for sheetrock, but I don’t’ think we can use the same standard for tiles on slab. Thank you

    • Jason Spangler says:


      Thanks for the questions and I am very sorry about your new house. Unfortunately, the 28-30% isn’t a scale that I am familiar with, nor is it a measurement scale utilized within the floor finishes community when speaking of concrete moisture. The usual scales will either be represented in relative humidity % when measuring in the concrete or in lbs of vapor emission when measuring on the surface of the concrete with a calcium chloride test. Sorry I can’t be more help.


  64. Kevin says:

    Hi are you recently had a flood in my kitchen a dishwasher pressure line broke and I have tile ceramic that was put over linoleum would it be possible that water would have gotten underneath the vinyl the insurance company does not want to remove it they said it was dry

    • Jason Spangler says:


      Thanks for the question. It could be possible, but might not be very probable. If you have a concern, you may want to find your own building inspector to come out and evaluate it for you, not the insurance company. This may be the only way for you to be sure. Good luck.

  65. Debbie Myers says:

    Hi Jason! Thank you for offering your guidance! We built our home 6 years ago. It has a concrete slab foundation and sits on a lot that is halfway down a slope, meaning that to the south of us there are homes sitting at a higher elevation, but behind our home the land slopes downward to a valley. We are having problems related to a high moisture level in our slab. The first problem that arose was that our original carpeting, a polyester “green” carpet, looked extremely worn within less than a year of it’s installation. The builder agreed to replace it. We used a nylon carpet and it has been ok. Also, there was cracking on our front patio – the builder agreed to install tile that we purchased to cover the cracks. Our home has mostly engineered wood flooring. The floors started to peel at the edges in the first year we were in the home. We thought it was wear and tear. Over the years this has gotten progressively worse. The wood has a 25 year warranty, so again I contacted the builder. They had a wood flooring specialist from NWFA come out. Using a pin-type wood moisture meter he tested the moisture levels at the surface and slab level. In 2 locations (front and back of house) the surface humidity level came to 9.3 and 9.4%. At the slab level the readings came in at 18% (back of house) and 20.8% (front). They also had a plumber test our lines – they all were fine. The builder declined to replace our floors saying that the slab moisture is high because we added a patio and pool on the back of the house blocking the moisture in the slab from escaping. (The sides and front of the house are not blocked in any way). The slab was not tested for moisture before the wood floors were installed – this builder “never does that”. I am not sure what direction to go at this point. Are there any tests that you would recommend? What do you think our next step should be? Thanks so much for your help with this!

    • Jason Spangler says:


      Thanks for the questions. First, slab moisture tests are usually a required part of installing a floor based on the manufacturer’s specifications and in order to get a warranty. I would start with having the manufacturer come out and evaluate the claim. Depending on your satisfaction with a remedy after this, you may need to get a geotechnical engineer out to evaluate the claims related to the patio and pool. Good luck.


  66. Thank you for taking the time to provide such an informative and helpful post.

  67. Thanks, Jason for your this kind of useful information. I’ve already suffered with my flooring moisture problem. I’m interested with your Rapid RH® 4.0 product. But I’ve a question that how to measure moisture.Thanks again

  68. T.R. Fluker says:

    Hello Jason,
    Is it possible for vapor emission to cause water to actually puddle on top of the floor when the floor consists of VCT on a concrete slab? I understand the VCT has been down a couple years with no problems and all of a sudden water started coming out of the joints in the VCT. The slab is probably more than 50 years old and does not have a vapor barrier.

    • Jason Spangler says:


      Thanks for the question. With no vapor retarder, vapor from the soil has a direct, unobstructed path to the slab. With the addition of moisture into the slab, a pressure differential develops with the ambient air, causing the vapor to want to rise in an effort to equalize the pressure. In these cases, moisture developing at the surface is definitely very probable.



  69. Luis R Vila says:

    HI Jason,
    I am replacing my wooden floors with solid wood floors. Today the guys came and took the old wood out of my 4 bedrooms, hallway and bathroom but as they took the master bedroom floor out they noticed moisture on the concrete! It is not very visible but as I run my fingers through some areas of the concrete I see the tip of my fingers are slightly wet. At first I thought it was a leak from the master bathroom or the windows but no water seems to be coming from either of those two places. The way they are installing the new floor is by first putting .5″ to 3/4″ of plywood and then nail the solid wood on top. I’m in a panic not really knowing what to do… Any thoughts? Thanks , Luis

    • Jason Spangler says:


      Thanks for the question. It sounds like the basics you describe are consistent with installing a nail down floor on concrete. As far as the moisture you were feeling, I would talk directly to your installer about that and see what he/she recommends. Good luck.


  70. Heidi says:

    Hello, I’m installing engineered hardwood floor on a concrete slab. We had carpet there for 10 years without an issue. Would you recommend insulating the floor before placing the new floors down.? It is a bit chilly on your feet in the winter. Thanks, Heidi

    • Jason Spangler says:


      Thanks for the question. Unfortunately, I can’t speak to the installation of insulation, prior to putting down the wood floor on concrete. I would consult a professional installer or contact the National Wood Flooring Association at Another option you may think about is some type of radiant heat under the floor. Good luck.



  71. Mike Buck says:

    Hi we seem to have a moisture problem with our laminate floor, it is laid on a concrete base the base was screed to level the floor and it has been down for about four or five years with no problems but recently we have noticed areas of water appearing on the floor overnight we have a de,humifier that collects quite a drop of water. Any ideas . Mike. uk.

    • Jason Spangler says:


      Thanks for the question. I would first start by determining if this is a dew point issue. Utilizing a thermo-hygrometer, measure the relative humidity and temperature in the ambient (room) air. Enter those two numbers into a calculator like this to determine dew point temperature. Next, take the surface temperature of the laminate with an infrared thermometer. At this point, compare the calculated dew point and the temperature of the laminate. The closer they are to each other, the higher the probability that condensation will form. Hope this helps. Good luck.


  72. Lilasa says:

    I forgot to mention in my earlier post that we live in Austin, Tx and we haven’t had any rain in the past few months. Also, the floors we had and will be putting down are engineered unfinished wood that are glued down. Thanks

  73. LilaSa says:

    Hi. We are having our hardwood floors replaced throughout the house due to a dishwasher leak that buckled a small area. Our one story house was built in 1959. When we bought it in 2000, we had hardwood floors installed in only a few rooms and tile and carpet in the rest. In 2009 we added on and remodeled the house and added hardwood to all areas other than bedrooms. The company that installed them is a very reputable company and we are using them again for the new floors. When they pulled out the hardwood floors, they did a moisture test and the moisture levels was very high. I am not sure exactly what tests were performed, but the guy mentioned something about a meter and a pin test. They got very high moisture readings in all areas of all rooms of the the original home/slab. Per their recommendation, we are having a plumber come out to do a hydrostatic test to make sure there isn’t a broken pipe in the slab. If there is not a leak then do we just have a high moisture slab? If so, has it probably always been this way? We have never had any problems with the hardwood floors or baseboards before. Do we need to have a barrier put on the floors before putting the wood back down?

    • Jason Spangler says:


      Thanks for the questions. As you stated early on in your question, you are dealing with an installer that you hold in high regard, so I would follow their and/or the various manufacturer’s suggestions to ensure a warrantable installation. It is common, no matter your locale, to find old slabs that have high levels of moisture. One of the main culprits for this is that IF a vapor retarder was used under the slab originally, it has probably degraded to the point that it is no longer effective, allowing for moisture vapor to move through the soil and into the slab. Even in dry climate areas, moisture vapor is present and can travel a great distance from below. Good luck.

  74. Jc says:

    Hi Jason. We bought a two story house three years ago. Six months ago we noticed a bad smell on the entire first floor. We also noticed some black spots through out all th ceiling of th first floor. I started cutting some of these areas of sheetrock and found out that the whole entire first floor ceiling has mold. We had previously removed all the first floor sheetrock, and removed the mold. We had painted the wood with some special paint to prevent this from happening again. We also had installed all new insulation on the first floor ceiling and walls. After we did this, we got rid of all the mold. The smell went away for couple of months. We noticed that the smell came back today. I removed a piece of sheetrock off of the garage ceiling. We then looked from the garage through the inside of the ceiling, towards the connected living room ceiling. When we did this, we found out that there was condensation on the inside of the ceilings again. (The garage and living room.) I also saw some mold on the new sheetrock. I don’t know what to do now. I brought an air condition company to see if that could be related to issues with my AC unit. I thought that maybe there might be too much humidity inside the house. They told me that it was ok. The second story floors, have laminate flooring. When we installed the second story floor, I installed a moisture barrier liner that was recommended by the hardware store where I bought it . Do you have any idea, what could be causing this? We know that the pipe work in the house are good, there are no leaks. That is why, I am wondering what else it could be. We live in the Houston area in Texas..

    • Jason Spangler says:


      Thanks for the question. If you have taken out any potential variable for leaks, I would be looking at the potential for dew point issues, especially given you live in a high humidity climate like Houston. Ventilation can be critical in these instances. Make sure your roof has enough ventilation and some people will also install thermostatically controlled gable vents that push and pull hot air once the attic temperature hits a certain level. Doing this may help to diminish the potential for condensation. In the end, having a certified building inspector out there may be a good way to know, for sure, prior to spending additional money on fixes. Good luck.

  75. Hello,

    We bought a used manufactured home a year ago and we took up the carpeted flooring this spring. We had installed a laminate locking floor after the carpet was taken up. Now we have a moisture problem. We went back to the people that did the work and they told us to get a dehumidifier, yes it pulls a lot of water out of it, but also the flooring is buckling and it makes creakibng sounds as you walk on it. We went back to the people that installed it and they said they will not come back and touch it until it is fixed. We have had several different people look at it and the last ones told us to keep the vents closed on the west side because a lot of wind and rains come in there. This is summertime and we have had not hardly any winter storms to speak of, but they will be coming because we live roughly a mile from the pacific ocean. I have talked with my neighbors and they do not have this problem as I have told you. Nobody yet has found the culprit and I’m getting more and more worried about this problem, because the fall and winter months are coming. We lived here last winter but then the floor was carpeted and nothing appeared, up until just recently after we had the laminate floor installed. My question is does it need to have a moisture barrier of some sort installed under those laminate planks??? I believe when I seen them being installed there was a light green paper or??? attached to the planks which would be the underside of them. We love the look but so far very unsatisfied with the results of the new floor and we want to know what can be done about it. We had a guy come out to inspect and NO leaks anywhere. But he was unable to see where the problem is. When we bought the house a guy went under the home to inspect and it came out in good shape. Now water——-would a “TRANSITION” help as the people that installed it said it might???

    • Jason Spangler says:


      Thanks for the questions. These questions you are asking about installation specifics i.e. moisture barrier under plank and transition strip, should be asked of the manufacturer of the laminate floor. Most have very specific guidelines for approved installations. Most floors of this nature have maximum dimensions before a transition is required to help with potential issues. Good luck.

  76. Angie says:

    We had new concrete poured for a patio. We did not tell them it would eventually be closed in as an interior room. One we enclosed the room, we had contracts put levelor on it, then we laid carpet. The room started smelling and we ripped out carpet. Needless to say the concrete wasn’t properly done for interior use. Are there any simple solutions to fix this aside from busting up the whole room and re pouring? Right now I’m having the deal with bare floor with levelor on it and it’s gets dusty. I don’t even like walking on it barefoot. I was hoping I could at least put a coating on it so it doesn’t feel so yucky, but thought that may cause more moisture Issues. I haven’t noticed it being damp since we pulled carpet out, but some of the levelor around edges have cracked. Thanks

    • Jason Spangler says:


      Thanks for the questions. There are mitigation type products that can be applied, topically, to the slab that will lessen the level of moisture that passes through, allowing you to install a finished floor. One issue may be that most will require application directly on top of the slab, not the leveler. I would consult a reputable flooring installer or flooring distribution business for potential recommendations. Good luck.

  77. Yvonne Dykstra says:

    we recently installed the vinyl floating flooring over a concrete slab from a previous garage (never used as a garage). the place is a cottage and not occupied during the week. we recently arrived and our temperatures and humidity levels outside were very high and we now have water all over our floors. we’re running a dehumidifier but yikes – what do we do??

    • Jason Spangler says:


      Thanks for the question. It’s hard to say if it’s one thing or a combination of things that are causing the issues. First, many garages are built without vapor retarders below them so moisture can potential infiltrate the concrete from the bottom of the slab, migrating to the surface. This may be some of the problem. Additionally, turning off all environmental controls makes perfect sense, from an economical side, when no one is inhabiting the cottage, but it has the potential to cause severe issues to the interior of the cottage. The moisture on the floors may be dew point condensation. If the temperature and relative humidity in the cottage were regulated, this may not be an issue. I hope this helps and good luck.


  78. Pamela Puskala says:

    We built a building with a concrete slab. The concrete was poured in August of 2017. We are now trying to figure out how to lay stone on the floor of the shower over the concrete. Do we have to seal the concrete first and then lay the stone and then seal that? or can we just lay the stone right on the unsealed concrete and then seal the stone and grout? Thanks for your help!

    • Jason Spangler says:


      Thank you for the question. With specific application/installation questions of this nature, I always recommend you contact the manufacture of the products you are going to use to install the stone. Whose thin set? Whose grout? They should be able to give you VERY specific installation instructions to ensure longevity. If you don’t find the information online, call their technical department directly. I hope this helps.


  79. Casey says:

    I’m renting and our carpet is on a concrete slab. The carpet always feels wet or damp. How do I go about getting the landlord to take care of this properly? Is there anyone in the city I can contact if the landlord brushes me off?

    • Jason Spangler says:


      Thanks for the question. If you think it is a health issue then quantifying the issue would seem to be the first step. Air quality testing would seem feasible. Other than that, I really have no other opinions to offer. Good luck.


  80. Sandra Bertoli says:

    Our house is entirely tiled and experienced a major water leak last week which covered most of the floors and flowed out under the front door.

    While surface water has been cleaned up, our plumber emphasized the importance of finding out what the optimum temperature and A/C setting should be to avoid tenting or buckling of the ceramic tile.

    Can you make a recommendation?

    Thanks for your assistance,

    • Jason Spangler says:


      Thanks for the question. You may have already seen this article, but if not, here is the link I would recommend talking with a remediation contractor in your area that may have specific experience on this topic. My guess is reasonable temperature with the addition of some type of dehumidification, if your HVAC isn’t suitably equipped, will be the prescribed method for continuing the drying process.



  81. Matea says:

    Dear Jason,

    is there any regulation/law that sais how high RH in concrete can be before putting tiles/parquete on it?
    I am trying to check RH in my concrete floor (after huge damage with water pipes) with device named TQC but there are 4 possible ways to check it and I cannot find which of them is most suitable for checking RH:
    1. Concrete 0-6%
    2. Crabidw method 0-4% H2O
    3. Relative scale
    4. 15. Scale

    Can you help me with advice somehow?
    Thank you in advance!

    • Jason Spangler says:


      Thanks for the question. This meter isn’t intended to measure RH levels in concrete. From what I have seen, wood floors are usually in that 75% RH range when testing concrete RH% in the concrete, but you should verify with the flooring and setting material manufacturer to make sure. Good luck.


  82. Tony Agostinelli says:

    I have a concrete floor with 24×24 rubber tiles installed on it that is “curling” at the edges of the tiles. When I pull the tiles back, the slab is damp to the touch and you can watch it dry out (color change) once the slab is exposed. However, when I ran a calcium chloride test, it came back 4.6, which should be ok for the adhesive. Any thoughts as to what I am experiencing? Why would a qualitative test “fail” (dampness under the tiles) and a quantitative test “pass”.

    • Jason Spangler says:


      Thanks for the comment/question. First I would ask, did you grind the 20” X 20” concrete area where you placed the CaCl test to a CSP 1 or CSP 2 and let it sit for 24 hours before setting the test? Second, this is a perfect example of why surface testing isn’t a real indicator of the long-term performance of a floor. The top ¾” of the slab may show “dry”, but once the flooring is installed, moisture deep within the slab will equilibrate, raising the moisture on the surface.



  83. A. James says:

    Contractors say the moisture levels are too high to install wood floors. We’ve tried fans, dehumidifiers, calcium chloride test, and had plumbers come out to check for leaks. Any other options so that I can get floors installed and my house back in order?

    • Jason Spangler says:


      Thanks for the comment. Without knowing the history of the home i.e. old vs new, is this just a renovation or was there a catastrophic event that caused the need for the flooring change (flood), I would recommend having a discussion with the contractor about options. They make products that will encapsulate the moisture in the slab and allow installation or better adhesives, depending on the level of moisture, that can do the same. The will cost more, but help with your issue. Good luck.

  84. John Hearts says:


    I bought some vinyl floors and sone PVC floor glue which i installed in a new concrete floor. 2 days after, a whitish liquid was coming out from the floor where i installed the vinyl floors. I removed the entire floor and installed brand new vinyl floors again and the same thing happened. Please what is the solution to this? Is it the glue or is it the moist from the new concrete floor? How do I solve this???

    • Jason Spangler says:


      Thanks for the question. The first thing to do is identify what the flooring and adhesive manufacturer recommend for proper installation of their product. In their installation documents, they will have requirements for what they call “sub floor preparation”. Here they discuss many things, but one is concrete moisture testing. Have you done any of this? If not, I would start there and then once you have that information, contact the manufacturers and ask for their recommendations on a proper installation.



  85. Cbb says:

    My husband and I are currently building a house and we’re hoping to use vinyl flooring for a budget friendly flooring. We had a friend/contractor to suggest doing a moisture test before purchasing any flooring. The first test (in Nov) it said there was over 7lbs in the floor. We did another last week and it is down to 6lbs, but according to our friend, that is still too high for VCT.
    The business we were going to purchase from is supposedly unaware of any need for a moisture test, and says it will be fine.
    Do you have any thoughts/opinions on this? Or know of any effective ways to draw moisture out of a concrete slab?

    Thanks an advance.

    • Jason Spangler says:

      Thanks for the comment. There are some adhesives that may allow VCT to go to a higher moisture limit. I would consult the VCT manufacturer and seek recommendations from them. Drying concrete is a matter of time and environmental conditions. Having HVAC units up and running is step number one to expedite the process. Good luck.



  86. Jim says:

    We finished our basement two years ago and chose a vinyl tile with grout for the bathroom. Less than a year after, some of the tiles buckled up at the grout line and were replaced by the flooring people, the thought was there was not enough glue. Into the second year more tiles did the same and the flooring people said there is a moisture problem. Not all tiles are buckling, so upon recommendation we removed the toilet thinking it may have a leak. The seal was good, so that was not the problem. The contractor did need to break the slab to rough in the drain for the toilet and shower. We have not removed the flooring to see if there is an issue with that. The floor outside the bathroom walls is either carpet or bare concrete, neither have moisture. Another part of the basement we have a vinyl floor product that interlocks without grout, not sure if it was glued, with no issues. The basement has always been dry before and we have always run a dehumidifier. The current thought is to remove the flooring and let it dry to see where the moisture is now. I’d like to know what we need too look for, and correct as a next step.

    • Jason Spangler says:


      Thanks for the comment. First, I would want to test the concrete to see how high the relative humidity is in the affected area, Second, the areas that you state don’t have a moisture issue, may. Carpet is very breathable and, obviously, so is bare concrete. The moisture we are speaking of here is moisture vapor, not physical water. So it may be coming up through the concrete and once it gets to the surface, it evaporates and is processed through the dehumidifier. One of the big issues with basement renovations is you never know if there is an intact vapor retarder under the slab and in most older homes there isn’t. Without that, moisture from the soil is always available to the concrete. They make products that can be applied to the surface of the concrete, prior to flooring installation, that help minimize the amount of moisture that can come out of the slab. The first thing is to determine how bad the problem is.



  87. C says:

    We have a luxury vinyl plank flooring and just months later the flooring is bubbled and glue squirts out anytime you step near a seam. These were professionally installed and were glued directly to a concrete subfloor. The flooring company insists I have a leak and won’t repair, but they also never completed a moisture test prior to installing. Do they have any obligation to repair?

    • Jason Spangler says:


      Thanks for the comment and I am sorry for your issues. Most contractors have some kind of warranty on workmanship, but in the end, they have the ability to decide whether this falls under their warranty. Depending on where you purchased the material, you might get some help from them, or possibly even the manufacturer of the product. Good Luck.


  88. Misty says:

    Good morning, we have lived in our house almost 7 years. We have stained concrete floors and have a huge problem with efflorescence. We have had the moisture test done where they drilled holes in the floor and we were told it is the highest they have seen. We are wanting to cover our floors but we don’t know where to even begin. Do you need to grind the stained concrete floors and what type of flooring would work with this moisture problem? Help

    • Jason Spangler says:


      Thanks for the comment. I would enlist a reputable flooring contractor to give you options. If the levels of moisture are very high in the concrete, there are various products on the market that can be applied to the surface (moisture mitigation product), to minimize how much comes out and can affect the flooring finish you wish to apply. Keep in mind, the high levels of moisture don’t bother the concrete, they bother the finish trying to be applied. I hope this helps.

  89. Justin Lee says:


    I live in north Tampa. I have battled water intrusion up through my grout lines in my newly installed porcelain tiles for over a year now. It occurs almost daily, pooling puddles, and a couple of times actually squirted through an opening when I scraped the efflorescence away. My home was built in 1980.

    When we first noticed the issue, end of 2015/early 2016, we saw water stain under our laminate floors. We filed an insurance claim and their investigation (sub-par at best) was negative for leaks and determined to be a ground water/seepage issue, which is not covered. It was denied. I remodeled my home and during the process of removing the damaged laminate, there was thick mold found underneath every sq inch. My kitchen cabinets base and my two bathrooms show water damage and were installed directly onto the slab, NOT the tile. There were 14×14 inch ceramic tile with a ¼ inch grout lines in the rest of the home, which never showed water or efflorescence. Even the un-remodeled bathrooms to this day do not show water intrusion. I installed 36 x 8 inch porcelain tiles with 1/8-1/16 inch grout lines. Well, I am positive that it is NOT a ground water issue through my own long term investigation by many different means, i.e. new gutters, surface ground drains, multiple drilled holes all the way through my slab with no signs of moisture, 5 holes- 4 ft deep, surrounding my slab on the affecting side of the house with NO ground water layers, new a/c return vent, correcting a negative air pressure issue within the home, and more. Im even having a couple tiles de-bonding. I also have a thinner, more powdery textured efflorescence showing on my garage floor and the paint has been flaking off. Over time, the leak locations have been slowly migrating further and further. The water is only on the surface of my slab. I haven’t noticed the slab insides being moist when drilling, or even in the dirt under the slab. I will add that I am on a pond, but it is approximately 40-50 feet behind my house with a major slope, approximately 3 feet lower elevation than my home.

    I have ruled out just about everything after 3 negative leak detections (1 included a drain inspection), 2 denied insurance claims, 3 geotechnical engineering firms blew me off (couldn’t figure it out and gave up), a building scientist unable to figure it out after almost 8 months trying, ruled out ground water, and more. This problem was consistent even during the 3 month drought we recently had. During this drought, the pond behind my home dropped about 12 inches in water level, but my water instruction continued just the same. The county water department and utilities departments both deny any possibilities of leaky pipes/drains on their end. Heavy rains do not seem to affect the frequency, nor does an extended time without rain. It’s major hydrostatic pressure and NO ONE is able to determine or even guess what the source is. I find it very hard to believe it would be condensation being as there was a couple instances where it showed pressure when coming through the grout. I occur on two opposite ends of my home, but not in the center area. I have even drilled holes through my slab, down into the earth and NO water showing in three different locations drilled. I cannot accept that NO ONE can determine a source for this water. None of my neighbors have noticed a similar problem, however, in the neighborhood due north of me, 3 or 4 homes have seen similar issues, just not nearly as severe. I have held off on installing major, overkill French drains around the perimeter of my foundation until I can define the source. Is it possible that it’s a newly exposed underground spring????

    I am willing to bet this would be your most challenging investigation yet, if you are able to help me out. Please text or email me anytime. The sooner the better. I will not stop trying until I solve this.

  90. Rosalie Atkinson says:

    I have lived in my apartment for about 10 years and recently an accidental water problem in the apartment upstairs caused some damage to my ceiling and kitchen floor. Management said my carpet was not damaged so did not need replacing. However, when I walk barefooted across the living and dining area which are carpeted the bottom of my feet feel dampness. Is there some way to determine if there is still moisture under my carpet?

    • Jason Spangler says:


      Thanks for the comment. There really isn’t a way, that I am aware, to test moisture in the carpet itself. One thing you may want to try though would be a visual test. Take some newspapers or paper towels and put them in a few areas, placing something on top of them to weight them down. Leave them for short period of time and see if the paper product shows any discoloration. Obviously, this doesn’t prove where the moisture came from, but it does show moisture.



  91. I had a bamboo wood floor laid that did not adhere to the glue, the home flooded over a year and a half ago , is there anything I can do to save my floor.

    • Jason Spangler says:


      Thanks for the comment. I would recommend having either a qualified wood flooring installer or a wood flooring inspectors come out and evaluate the floor to determine a course of action.



  92. Martine Cameau says:

    Hello Jason, any thoughts regarding my post dated June 16? We hired a geo Engineer who determined that we don’t have a high water table, however there may be have been a drainage issue, as the soil samples indicates that one side of the house is about a foot wet. Likely soils holding water. Somehow it’s seeping into the area of dirt BETWEEN the slab and footer and has been wetting the soils under our floor. And we contacted the tile manufacturer; it seems the porcelain tile is creating condensation and it’s finding its way through the grout and our walls. We’re trying to figure out if there’s a way to dry the slab without having to rip out all of the tile.

    • Jason Spangler says:


      First, I apologize for missing the original question. I am not aware of being able to “fix” this problem without starting over. That being said, it may be beneficial to have a tile certified flooring inspector come out and evaluate and give some advice. I would start here ( and see what this organization can do to help.



  93. Taj Ahmad says:

    We have fully renovated our house this year. One of the major jobs was to put marble (Crema Marfel) on the floor. The floor was laid in February 2017. Two months later, we noticed powder like substance appear on the surface. We pointed this out to the contractor, who arranged for a chemical to be applied and buffing carried out. After the buffing, the the floor appeared clean and shiny. Two months later the problem appeared again. The contractor has arranged the application of chemical and buffing three times but each time the problem reappears after 3-4 weeks. We are now noticing dark stain marks on the joints. We moved into our house in March 2017, but have not been able to settle down because of the floor problem.

    Can you help with identifying the cause of the problem and proposing a solution.

  94. Jeffrey W says:

    My wife and I purchased engineered floors for our home, which is on a concrete slab. They were initially installed floating with a 3mm underlayment. Unfortunately, the slab was not leveled properly, which led to a number of dead spots and possibly buckling. So, the floors are being redone and the slab is being properly leveled. My questions are… I am concerned with moisture as the home has previously had moisture and mold issues. What is the best glue to provide a solid moisture barrier between the slab and the wood and/or do I still need an additional underlayment between the slab and wood in addition the glue (my contractor says no)? Thank you.

    • Jason Spangler says:


      Thanks for the comment. Your best place to start for best installation practices for wood is the NWFA at They have resources and phone numbers you can call to get expert advice. Regarding adhesives, you need to have appropriate moisture testing of the concrete to know what needs to be done to remedy the problem. I would start there and then based on the moisture testing results, you can shop for appropriate products to go on top of the slab.



  95. Martine Cameau says:

    Hello, we’ve been dealing with a moisture problems since we installed porcelain tiles in five rooms in our home built in 1989 (the rest of the house has ceramic tile that has been in place for 15 years). We had a drainage problem on one side of the house that resulted in wet walls (interior, not exterior) as well as major efflorescence in the new tile installation. We are currently in the process of installing well pointing and a sump pump to drain water away from the house. We are located in FL, and it’s raining every day here, and in on the rooms you can actually see water beading through the grout lines, but only in the middle of the room. We’re hoping draining water away from the house will ultimately dry out the slab. After reading the posts above, it seems the tile installer should have put down an epoxy resin before setting the tile. Is there any way we can do something to the EXISTING installation, and not have to resort to removing all the tile and starting over? Could we regrout and add something to the grout mix to help with the waterproofing?

  96. Sam says:

    Today we had a home inspection and during the inspection of this home we are interested in purchasing was built in 2010. The garage show efflorescence on the bottom concrete blocks around the garage foundation slab on some of the cement whitish residue on the surface. The home was built on a raise slab. We are not sure if we should purchase home ? If the would be a problem in the future ? What type of repaired is needed and the cost if all. Currently considering purchase but not sure if this is a major problem or could be a problem in unseen surfaces of the home.
    Please help or advise .

    • Jason Spangler says:


      Thanks for the comment. I would recommend contacting a waterproofing contractor and see if it is a big issue. In general, this is a fairly common occurrence, but you should verify your specific situation.



  97. dawn pecunies says:

    good morning, I just got up this morning to find that my ceramic (white)tiles in my kitchen are turning “gray”it looked like
    it was a shadow but with closer inspection the tiles are turning a dark grey. WHAT would cause this to happen???

    • Jason Spangler says:

      Dawn, overnight like that, being honest, I don’t know. I would contact a local contractor whom specializes in tile and/or contact National Tile Contractors Association ( and see if possibly they have any recommendations of someone who can take a look at it.

  98. Gena Jenkins says:

    I am having an issue with my hardwood floors. The floor is turning black although the house. They are not rotten, just turning a dark color. The areas are in my closet, under my rug in the dining from, as well as in my kitchenew

    Would this be a foundation issue or the floor not being put down correctly?

    • Jason Spangler says:


      Thanks for the comment. It would be best to have someone look at your issue because it could be multiple things. I would contact and get one of their qualified inspectors to come out and take a look.


  99. JILL COX says:


    • Joe Dabbs says:


      I am pretty sure that this old home does not have a vapor barrier. If I had a hunch you probably see more “wet” concrete during the wet months when compared to the dry months. I say this because your concrete slab is like a sponge and it will soak up moisture when it is present. One of the ways to outsmart this problem is to create a “vapor” barrier on the surface of the slab. Epoxy Resins are applied to the surface to keep the moisture from escaping from the surface. If done correctly, the epoxy resin should create a barrier strong enough to defend “moisture”.

      Here is a link that explains this process in more depth:

      Let me know if you would like some more information or you can give us a call at 800-634-9961.

      Thanks Jill,
      Wagner Meters

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