Grout Problems: Can Concrete Moisture Taint Your Grout?

Tiled HallwayTile floors have never been noted for being susceptible to moisture problems, but lately, there has been an increase is moisture-related problems in tile flooring installations.

Is the change in performance a result of different materials, different processes, or a new awareness of how moisture conditions in a subfloor can have a long-reaching impact on a floor’s performance?

The answer is…yes. Changes in a variety of elements connected to tile flooring have made it potentially more sensitive to moisture conditions that usually begin in the subfloor.

What Changed?

When ceramic tile made up the bulk of the tile industry, tiles were typically a smaller size (12” by 12” was standard) and were somewhat permeable so they could absorb or allow trace amounts of moisture to pass through. A standard installation would involve larger grout lines, and the tiles would either be applied directly to a subfloor slab or mortar bed or separated from the subfloor by plastic sheeting or asphalt building paper. If there was moisture present, it either had room to escape the from the tiles or was isolated from it.

But that has changed. Tiles are now often significantly larger, with thinner grout line allowances, and are made from low-perm or impermeable materials. Application methods have changed, with thin-set applications or moisture-sensitive adhesives and underlayments commonly in use. Additionally, construction schedules are rigorous in their time restrictions, often not adequately allowing time to ensure the concrete subfloor is completely dry. It all means that tile floors are less forgiving of excess moisture because it has few places to escape and more impact when it can’t. Grout will often show the first clue when a moisture problem exists.

Signs of Trouble

Discolored Grout

Grout FailureGrout discoloration is often the first sign that there is a moisture problem on a tile floor. It is caused by moisture entering the grout, either from above or below. Grout tends to be more porous than tile and so provides an easier pathway for moisture to travel beyond its bounds.

If the concrete slab below is the source of the excess moisture, that moisture will have worked its way from the bottom to the surface, so discoloration is a sign that the moisture has been present for some time. Moisture can soften the grout, making it more prone to crumbling or damage, or it can result in efflorescence as moisture evaporates away.

Efflorescence on Grout

Efflorescence is a whitish powdery residue that can appear on grout (or on concrete) over time. It is typically caused by water-soluble minerals in the concrete mixture (or the grout) dissolving into any moisture that is present, which then are transported to the surface during the drying process. As the moisture evaporates from the surface, the minerals are left as a residue that collects on the surface of the grout.

Moisture Testing for Concrete Subfloors

Cleaning GroutThe bad news is that if concrete moisture migration is causing discoloration or efflorescence of the grout on your tile floor, it can be difficult to address adequately. Efflorescence can be removed with acids or solvents but may reappear if the moisture problem is not addressed and corrected. Using acids or strong solvents can also significantly change the appearance of the grout. There are also penetrating sealants that can be applied to slow the rate of evaporation from below. Obviously, any remedy will need correct and careful application.

The good news is that with accurate moisture testing before the tile is laid, a concrete subfloor can be eliminated as a source of problematic moisture. The key is to choose the correct type of concrete moisture test.

There are two generally accepted moisture tests for concrete slabs that will have flooring installed on top of them – calcium chloride (CaCl) testing, and relative humidity (RH), or in situ, testing. However, when considering the lifespan of the floor, RH testing provides the best concrete moisture testing to prevent moisture migration problems in the installed floor. Why? Because only RH testing can predict the final moisture level of the concrete slab over time.

Free Download – 4 Reasons Why Your Concrete Is Taking Forever to Dry

CaCl testing works at the surface of a concrete slab, estimating the amount of moisture in a slab based on the amount of moisture vapor absorbed in a desiccant material sealed on the surface for 72 hours. While there is no scientific basis for this test method, it has been generally accepted for decades as a go/no-go indicator of whether a slab is dry enough to accept a flooring installation.

The difficulty with the CaCl test method is that while it may give an indication of the conditions on the surface of the slab (and even there it has proven problematic in its results), it cannot give any indication of the overall moisture levels in the entire slab. In fact, it has proven to be so problematic that CaCl testing has been specifically disallowed as a test method for lightweight concrete. Moisture migration in a drying slab operates as a cycle that moves excess moisture from the bottom to the surface and continues until the slab has either reached equilibrium with its ambient conditions or until the slab is sealed.

Once the slab is sealed, moisture will continue to move within the slab until it has equilibrated, which may bring the moisture level on the slab’s surface to much higher levels than the CaCl test indicated at the time.

Rapid RH L6 sensor pack with sensor in concrete slab

RH testing, like with the Rapid RH®, however, places a sensor within the slab at 40% of the slab depth (for a slab drying from one side), a depth proven through years of testing to indicate what the final level of the sealed slab would be if the slab were sealed at that point in time. Barring the introduction of a new source of moisture (a perforated moisture barrier or a leaking appliance, for example), RH testing allows for the final stage of equilibration that occurs within a concrete slab once the slab is sealed.

That is the moisture level that is critical to the continued success of your tile floor and the grout that holds it together.

For a tile floor that maintains its beauty both within and between the tile, RH testing provides the best possible moisture test method for ensuring a long-lasting and durable finish.

Last updated on August 23rd, 2023


  1. Lynn says:

    My husband and I renovated an our 1980’s home. The old floor was pulled up with a jack hammer and a new one laid. The work was subpar so the floors had to be pulled up again, with some type of equipment, smoothed out and laid again. After we removed the grout haze using a haze remover, we started noticing moisture in the grout lines. It has progressively gotten worse. I was wondering if the haze remover could have been the reason for the moisture starting to show? There wasn’t an issue with moisture until we used the cleaner. The efflorescence is really bad as well. We were thinking the moisture should stop due to a lack of rain, is that a reasonable conclusion?

  2. Chaney says:

    Okay so I need advice, We got LVT flooring put in and it was grouted. We live in a by level home and we got it installed by a professional flooring company. They put it in the whole basement. They didn’t warn us that basements collect moisture and they didn’t offer us to water proof it at all. I know now that its common sense to most people, but I wasn’t aware of it at the time.
    Well 4 months into it we notice our grout start to change color, It was gray, now its brown in most places, and the moisture started to come up in certain areas if you stand on the LVT. The moisture smells like permanent marker.
    So we contacted the flooring company and they said get a de humidifier and let it run for about 4 weeks and see if that moisture goes away.
    So 4 weeks later it helped out a little bit with the moisture but it still comes up in some areas, the grout is still discolored. So the flooring company sent us a quote to tear it up and apply a moisture barrier. the moisture barrier is called “Taylor Sahara 2 Gal. Moisture Vapor Barrier”
    Then re apply the LVT.
    Do you think that would work? Or would we see the same problem come up in another 4 months?

    • Jason Spangler says:


      Thanks for the question. First of all, did they do any moisture testing prior to the first installation? Were those results appropriate for the initial installation? It seems odd that they weren’t able to identify a potential issue prior to the first installation if they did proper moisture testing. Next, in theory, the Sahara would work fine, but they have a couple of details in their technical data sheet that will need to be verified:

      An intact moisture vapor retarder must be present below the concrete (see ASTM E1745), must be fully cured (at least 45 days), porous (see ASTM F3191), without hydrostatic pressure, without pressurized liquid from any source, and free of surface alkaline salt crystallization.”

      The bolded items are what I am speaking to. The only way to verify an intact vapor barrier it to do what is called a core sample of the concrete slab to expose what is below it. Hydrostatic pressure isn’t something that happens a lot, but when it does, it is more times than not in a basement like floor. Good luck.

  3. Jeanne Wojo says:


    I just noticed that some of the floor grout in our sunroom has gotten dark almost overnight. The sunroom is over the garage. Could this somehow be moisture coming up from the garage? If so, how would I fix that?

    Thank you!!

    • Jason Spangler says:


      Thank you for the question. I highly doubt this is being caused by moisture coming up from the garage. If cleaning doesn’t work then it might be worth taking a small section of the grout out and seeing what is below. Good luck.

  4. Ben Davis says:

    I had a contractor remodel our bathroom. We moved the old bathtub and changed the plumbing for the new one.

    I noticed the grout in some areas was discolored. We resurfaced the grout a few times, but eventually it became discolored again.

    I asked the contractor about what may possibly be causing this issue. He said they chiseled out the cement from an area for the new bathtub.

    Did they not properly cement in the foundation where the tile is laid ? Did they not seal it properly ? What could it be ?

    The new bathtub has a plastic drain underneath it ( which I’m not happy about and later found out) but that probably isnt causing the issue now. It may be problematic eventually)

    Thank you all !

  5. Joe says:

    Please help.

    Home inspection identified active moisture (40 reading on the meter) in 2 of the 4 bathrooms of the home we are in contract to buy. Seller agent stated that the floor was recently cleaned and didn’t dry but we checked 6 hours later and the grout was still dark around the tub and toilet. Is this a major issue worth not buying the home over? The home was built in 2019 and the two bathrooms in question are next to each other which concerns me.

    • Jason Spangler says:


      Unfortunately, I’m not sure what the term “active moisture” means or how to quantify it. Having elevated levels of moisture around the toilet isn’t uncommon. As far as whether this is a big issue, you will need to answer this question yourself. Good luck.

  6. Dahlia Duffy says:


    I live in Southern California and we have grout problems in the bathroom along the floor tiles. When we moved in the bathroom floor is porcelain tiles. I had the tiles changed because I did not like what was there. Now we have constant problem of grout crumbling. My husband said the guy who replace the tiles when we moved in probably did not put there right thickness or type of subfloor. However, I think there was a good subfloor there because the tiles that used to be on the bathroom floor did not squeek or move.

    Our problems is my husband will keep repairing the grout, then it will break or crumble after 2-3 weeks. We hired a “licensed” guy to fix our grout and he said he will put the grout that is strong with sealant and that this grout will dry at once since we only have 1 bathroom. But now the grout crumbles after 3-5 days of repair. The guy comes back and put the grout but I am tired of them coming back and the grout does not stay. Even though the grout they use dry fast we do not use the bathroom until after 6 hours to give it some time to rest but still after 3 days it crumbles.

    What is the best grout I need to use?
    Is the “fast and easy dry” grout not good and easily crumble?
    What do you think of those grout epoxy?
    What do you think of grout caulk?
    Should we use sanded or not sanded?
    What type of protection should we put on the tile and grout so our grout can be mopped with a bathroom floor cleaner formula product?
    What is the best cleaner for floor tile and grout to use with a floor mop?

    Thank you.

    • Jason Spangler says:


      Thanks for the email. Honestly, it sounds as if the subfloor isn’t stable enough and it is flexing, causing the grout to flex and break. The first thing I would do is have a qualified tile inspector come out and evaluate what you have going on. I would start here to find one NICFI – National Institute of Certified Floorcovering Inspectors,

      Good luck.

  7. Cindy Lasky says:

    I live in South Florida. I have tiny beads of water around 2 tiles in my living room. Do I need to have all the tiles removed and retime the room? Thanks for any help.

    • Jason Spangler says:


      Thanks for the questions and sorry about the issues with your floor. Your question really doesn’t have an absolute answer because I’m not sure about your ultimate goal. You (and I say YOU because you probably wont find a flooring company that will do it due to liability) could replace the two tile, but you haven’t found the source of the problem and it will probably happen again. Is this acceptable? If so, then I would question why even mess with the tiles if they are tiny beads. In my opinion, you need to have someone look at the floor and evaluate it to determine why it may be happening and then formulate a plan. Here is a flooring inspector group that may be able to help you understand the why Good luck!

  8. Nathan Vlasaty says:

    I live in Orlando and we had floors redone when we moved in about a year ago and I noticed at the time some areas of the concrete had moisture. Tile installer didn’t think it was an issue. In the past month I see one area ( not the area I saw after tile removal) with 5 or 6 spots in a 10 x 10 area with moisture seeping up through the grout. Anyway to alleviate this? I put damp rid in the area and that didn’t do much.

    • Jason Spangler says:


      Thanks for the questions. First, I would want to rule out this is a dew point issue. Condensation will form on a surface if the air temperature and air relative humidity are such to promote it. I typically wouldn’t bring this up, but being in Florida, it may be an option. This section of floor may be cooler that the rest of the floor and,or it may be around a register that causes it to be cooler. Here is a calculator where you can plug in the air conditions So get the air conditions, plug them in, and compare the calculated dewpoint to the floor temperature. You get this with an infrared thermometer. If this isn’t the case, you MAY be able to replace the grout with a less breathable formulation, but doing that may cause issues to manifest in that area under the tile. Good luck.

  9. Rebecca Gardner says:

    I was surprised when you said that grout can become discolored due to a moisture problem with the tile. My husband and I need to hire a cleaning service because the grout on the tile floor in our bathroom has started to look dark since we moved in last year. I’ll have to ask them if the discoloration looks like moisture damage or if it’s just dirt and grime!

  10. Hi Jason,

    We live in Houston, TX and about a year and 1/2 ago, flooded during Hurricane Harvey along with many, many others. Our entire downstairs from floors to ceilings were torn out and approximately 4 months after the flood, we had new porcelain tile installed all over our first floor. Several months after the new install, we began to see efflorescence coming up through the grout in multiple areas all over the house with the exception of 3 small rooms. It seemed to emerge strangely in that 1/2 of the same grout lines would be fine and the other 1/2’s covered with the efflorescence. To date, the effected areas have been dug out multiple times and grout replaced only to have it grow back each time. Approximately 2 weeks ago, all grout everywhere was removed completely and re-grouted with a supposed new product that was guaranteed to stop the efflorescence. The next day after the new grout was put in, we noticed the same trouble spots still looked wet. (And there are many!!) The installer said it was because the grout in those areas hadn’t completely dried and to give it about 5 days. We knew what was going to happen and sure enough, well before the 5 day “drying period” was up, the efflorescence began coming through again in those same areas. The installer wants to start the whole vicious cycle all over again by scraping out the efflorescence areas and re-grouting. Is it possible that an absence of thin set in those areas is allowing moisture from the slab to continuously seep through? Any help/advice you could offer as to which direction we should take would be greatly appreciated! We are tired of having our grout re-done time after time and see no end in sight. We are also not the only house on our street experiencing this problem. The installer has given us a lifetime warranty but we prefer to have things resolved during our lifetime! 🙂 Thank you!

  11. Giana says:

    We live in Southeast Florida and my home was built within the last year. We noticed in random areas of the home our grout was discoloring (dark spots) very similar to the picture you show on this page. The flooring company hired by the builder would come in and scratch out the grout and apply new grout, however in a matter of time the dark spot would come back and would show up in other areas throughout our home. By what I am reading it sounds like there was extra moisture on the slab when the tile was first laid? Approximately 1 1/2 months ago, the builder had the tile company come in to stain the grout (has a built in sealer) So far I do not see anymore discoloration the grout. If the problem was due to excess moisture, do you think the staining/sealing will help? If not what would be your recommendation?

    • Jason Spangler says:

      If the tiles are functioning properly, then the moisture may not be a real issue, except that it causes discolorations in the grout which is usually more of a cosmetic problem than a functional one. My guess is the “issue” is still there, it’s just no longer noticeable due to the stain. It wouldn’t hurt to get a local, second opinion and see what they think.

      Good luck.

  12. Brian says:

    We have had a house built finished in may 2017, since the we have a continuous leak on interior downstairs floor. Along stairway wall , substance would appear, yellow sticky substance appearing 10?ft along wall. Removed base molding and drywall in garage to look inside wall, nothing. To me, something happening under floor, but not a consistent occurrence. Any clues, builder not helping!

    • Jason Spangler says:


      Thanks for the comment. You may want to have a flooring inspector come out and evaluate the problem. It may be a moisture problem in the concrete, a condensation issue because of the temperature differential between the garage and the interior of the house, or something else. Issues like this are hard to diagnose via email. Here is a link to an association of floor covering inspectors Good luck.


    I have the exact same problem as Dave… But I’m in Florida. My house is 2 years old and after about 18 month we too started having crumbling grout and tile lifting. After hurricane Irma i noticed water under my bedroom carpet, when i lifted it up i found cracks in the foundation in which water was coming from (confirmed by my insurance guy). I was wondering if cracked foundation can do this to tile or what may be the cause? Perhaps the cement wasn’t cured long enough when they put the tile down… Is that possible?

    • Jason Spangler says:


      Thanks for the question. There are numerous potential culprits here and, yes, one of them could be the concrete wasn’t allowed to dry, not cure, long enough. You may need to have a geotechnical engineer diagnose the issues with the slab or you may want to start by having a knowledgeable flooring inspector take a look and diagnose the flooring issues. There are a few different inspector associations you can find via Google. I hope this helps.



  14. David says:


    I have recently experienced slab Leakes in my home and have had my tile grout line crack as well as portions of tile lift. My insurance company have sent out a tile person as well as a flooring engineer to inspect the cause of the lifting. Of course they stated the lifting is not from the slab leaks and it is due to poor installation or resent rains we had in California over 6 months age.

    I am looking for information on proper posture test for a tiled slab. My understanding is there is an ASTM test that is standard. I am trying to find the information on this but only find stuff on concrete test not tile after installed. This is important as the flooring engineer spend about 5 minute performing a posture test on the tile and I feel this is a little short for porcelain.

    Thank you for you help.

    • Jason Spangler says:


      Thanks for the comment. I apologize, but I am not understanding your question. What type of testing are you trying to have performed? If you are looking for moisture testing, the ASTM standard is F2170. I understand the tile is failing, but I am not sure of the rest of the question.



  15. andrea bouvier says:


    We have been living in a house SE of Phoenix, AZ since 2010. I first noticed some staining to the concrete patio that looked dark grey as compared to the rest of the patio.. Looked like it had been wet and was drying….that was my first impression. I even asked a concrete contractor about this stain when I was having this patio added-onto with more concrete in a different location. He didn’t seem all that concerned or knowledgeable as to what it could be.
    Fast-forward to now and there is moisture with efflorescence coming up in our living room tile grout in a significant but not majorly significant part of the floor. ITs noticeable to me because I mop the floors. To others, it is not something they notice unless I tell them about it.
    The spot on our back patio has become larger, too.
    We installed this tile about 4 years ago. When the man installed our ceramic tiles, he didn’t mention noticing any spots on the slab. Prior to this, there was carpet and I never noticed any moisture in the carpet in these areas.

    Do we need to be concerned? MUST this problem be fixed? Our tiles seem fine except for the efflorescence.
    I also have a concrete contractor coming out next week because my husband and I want an estimate to beautify our back patio with stamped concrete or similar.
    Is this is bad idea?

    Help! Thank you.

    • Jason Spangler says:


      Thanks for the comment. Personally, if the floor is performing as desired, I would just keep an eye on the interior issues. As for the exterior concrete, I would continue discussing your concerns with the professionals you are seeking to contract. Hopefully, one of them will have an explanation that makes sense to you. Good luck.


  16. Jean Demers says:

    I live in a free standing condo (villa). Over the past four years, I have had three floors installed. First was a laminate wood floor which began squeeking on the joints right after it was installed. The flooring company agreed that this was not something that we should have to live with and said that they had never had that happen before and agreed to rip it up and put hardwood. Within 6-8 months areas of the hardwood became black and started to spread. I found out it was moisture, but the company said they had tested and the slab was dry. I remember them doing that. Once again the floor was ripped up and the only solution I was told was tile. Now I have a porcelin tile floor where in the same areas that the black hardwood was, the tile grout is powdering and some areas of the grout are turning black. I have reported this to the condo association and they had Sleuth come in and do an investigation. Sleuth did find excessive moisure but nothing has been done so far. I have spent $14,000 on this floor. The association is afraid I am going to sue, but I’m not sure who’s fault it is. Can you help me? I don’t want money, I just want my floor fixed once and for all.

    • Ron Smith says:


      I’m sorry to hear of the complications you’ve had with your floor. Can you give me a call so we can discuss this further? I can be reached at 1-800-634-9961. Feel free to ask for me directly. Looking forward to hearing from you.

      Ron Smith
      Wagner Meters Sales Manager

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