Moisture Problems between the Flooring and the Slab

Laying Ceramic Tiles

It is no surprise to say that water is an integral part of the hydration process of concrete. However, allowing excess moisture to leave the slab once it is poured is just as crucial to a flooring installation.

Once the slab is poured, the excess moisture must leave the slab in order to strengthen the concrete bond and to permit successful flooring installations. Moisture-related damage to flooring materials is, of course, possible, but the real risk to a successful floor lies between the concrete slab and the flooring itself.

Three common floor materials run the risk of moisture-related problems.

  • Adhesives
    Flooring AdhesiveMoisture-related adhesive failures have always been a problematic reality in the flooring business. In addition, with recent trends towards restricting volatile organic compounds (VOCs) in flooring adhesives, there has also been an increase in the number of moisture-sensitive adhesives in use. If the adhesive being used to install the flooring does not have the correct moisture tolerance for the concrete subfloor, the entire installation can be at risk.
  • Floating Floors
    The attraction of floating floor systems is that they do not need to be attached directly to a subfloor. Instead, the floor pieces “lock” together to become a cohesive unit that is not as subjected to seasonal shifts, dimensional challenges or other moisture-related issues. In fact, floating floors are often the recommended product of choice for floors where high moisture situations may present issues with standard attached floor systems. For these floors, manufacturers often recommend the installation of a moisture barrier between the subfloor and the floating floor to prevent moisture intrusion. The difficulty, of course, is that if that barrier is compromised in any way, moisture from the slab beneath can still damage the flooring or finish.
  • Grout or Cementitious Bonds
    Excess moisture issues in a grouted tile or mosaic floor will often appear as efflorescence, a whitish residue on the surface of the grout. It’s the result of water-soluble minerals being dissolved by the moisture within the slab and being transported to the surface of the grout where the moisture evaporates away, leaving the minerals as a visible residue. The more porous the concrete or the grout, the more likely efflorescence will appear. In the majority of cases, these minerals are actually part of the concrete slab mixture (or possibly in the ground beneath the slab, if no moisture barrier was installed). If the slab was not effectively dried before the tile was installed, the natural moisture migration of the drying concrete will impact the grout, and remediation steps will be necessary to correct the problem. In extreme cases, excess moisture can lead to flaking or chipping of the grout and a complete grout or thin-set failure.

Moisture in a Concrete Subfloor

Are you seeing a theme yet?

Moisture control is often one of the most crucial, yet most overlooked, elements of any floor’s success over time, and that means accurate moisture measurement, beginning at the slab.

RH Testing in the FloorAccurate concrete moisture measurement is best achieved with relative humidity (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 in the drying process, so 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.

Because we at Wagner Meters have been assisting flooring professionals for over 40 years, we have also designed some of the most accurate and innovative testing methods on the market today.

Our Rapid RH® 4.0 is based on decades of scientific research and technological advances to help each builder and flooring specialist accurately determine the correct concrete RH level for his or her chosen flooring and products. Our innovative Easy Reader™ and factory-calibrated Smart Sensor design mean that results are quick, simple and reliable. The Rapid RH® line of products is affordable and conforms to ASTM F2170 requirements for easy recording and reporting.

We also understand that sometimes a building project schedule means making alternate choices in adhesives or even flooring products, and the Rapid RH® can help you make informed decisions. Along with accurate, actionable testing, we’ve also compiled a one-stop list of manufacturers that provide an RH tolerance for their flooring products at www.rhspec.com.

The truest way to protect a floor system is to be sure that all components are safe from excess moisture intrusion from any source. The Rapid RH® helps you be sure that your concrete slab will not be the source of a moisture-related flooring adhesive or grout failure. Don’t let moisture problems come between you and a successful flooring installation.

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Jason Spangler

Jason has 20+ years' experience in sales and sales management in a spectrum of industries and has successfully launched a variety of products to the market, including the original Rapid RH® concrete moisture tests. He currently works with Wagner Meters as our Rapid RH® product sales manager.

11 Comments

  1. JILL COX says:

    i HAVE BEEN REMODELING MY 50 YEAR OLD HOME..I REMOVED ALL THE CARPET AND HAVE VINYL/FOAM BACKED FLOORING INSTALLED. NOW, A COUPLE OF YEARS LATER, THERE ARE MULTIPLE GRAY AREAS THAT TURN BLACK ALL OVER MY HOUSE. WHEN I PULL BACK THE FLOORING “BLACK WET CONCRETE IS THERE…LOTS OF MOISTURE…WHAT BARRIER DO YOU RECOMMEND I USE WHEN I REMOVE/REPLACE THIS FLOORING? EVEN AREAS THAT HAVE NO FLOORING YET,,,WHEN SOMETHING SOLID IS SIT ON IT, OVERNITE, THAT AREA UNDERNEATH WILL BECOME WET. ANY HELP OR TIPS WILL GREATLY BE APPRECIATED. THANKS

    • Joe Dabbs says:

      Jill,

      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: http://www.vanguardconcretecoating.com/resins.htm

      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

  2. 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:

      Gena:

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

      Thanks,

  3. 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 (http://www.tile-assn.com/) and see if possibly they have any recommendations of someone who can take a look at it.

  4. 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:

      Sam:

      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.

      Thanks,

      Jason

  5. 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?

  6. 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:

      Jeffrey:

      Thanks for the comment. Your best place to start for best installation practices for wood is the NWFA at http://www.nwfa.org. 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.

      Regards,

      Jason

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