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Question DetailsAsked on 2/1/2014

concrete slab problems

We had a company install engineered wood floors on a concrete slab. Within a couple of weeks after the installation the floor started cupping in about a 20 square foot place in our bedroom. We had a wood floor specialist come out and it appears we have some moisture in the concrete and also installation was not done to spec on the can of glue. Wrong trowel used. Called a plumber no leaks anywhere. Now we are between a rock and a hard place. No one seems to be able to direct us what we need to do next. Most companies that deal with moisture usually do it under a crawl space and not on a slab on the ground. So now we can't do anything until we can find where the moisture problem is coming from. I just want to be able to enjoy my home without part of my floor removed. We can't do anything until the mystery is solved. Any ideas on what we could do would be helpful. Just need to find out what the problem is and be able to fix it. James Reese

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3 Answers

Voted Best Answer

Proper grading is important as stated above. In addition, I once had a customer whose home was built over a naturally spring fed pond which had been filled in. Of course they didn't know that when they bought but developers will put houses everywhere they can to maximize profits. Do you know the history of the property and whether there are springs in the area? It is a possibility. Also, many tract home builders do not properly install the vapor barrier under the slabs before they pour concrete. Concrete isn't water proof so any ground water easily seeps up.

To stop the moisture you can remove the floor and seal the foundation before reinstalling the floor, assuming it can be saved. Unfortunately, there is nothing that can be done (as far as I know) to seal the foundation with the flooring in place. Send a written request to the company that installed the floor for proof of an acceptable moisture test prior to installation. If they can't provide one consult with an attorney. You may have a legal case against them for not installing the flooring properly. The moisture may not be their fault but if it can be proven that a test would have shown a problem prior to installation they may be on the hook for the damages.

Answered 6 years ago by Todd's Home Services


It appears you have water perking up through the cement slab. This can be caused by improper drainage around the house. Check the exterior ground to see if you have any low spots next to the house. Also check to make sure your downspouts have extensions that carry the water at least 5 feet away from the house. If you have low spots, AKA negative grading, these should be filled in with soil. All the ground should slope about 1 inch per laterial foot for at least 5 feet away from the house. In other words the ground needs to slope away from the house for a distance of 5 or more feet to properly shed the water away from the house.

If you have a low spot or a downspout without an extension in the area where the water is infiltrating, this could be your problem. Make the corrections and see if the problem stops.

However, you wood floor is already damaged and will most likely need to be replaced. If it is solid wood floor it might be able to be sanded to smooth out the cupping of the boards. You must correct the moisture problem before you repair the floor. Otherwise the problem will return.


Answered 6 years ago by Homefront Inspection


Good answer right there.

Grading and poor gutter diversion are the biggest issues we see.

Answered 6 years ago by Davidhughes


1) on the moisture test Todd talked about - if a contractor came out and proposed a flooring for you that was unsuitable for the moisture conditions present, you MIGHT have a case against him - but it would be tough as heck to prove that at the time he did the test the moisture was excessive, especially since at that time it may not have been. An exposed slab will commonly dry enough, especially if in a ventilated area, that it would test fine. However, you then put a vapor retarder flooring over it (almost anything but open eweave carpet on breathable padding), the humidity underneath will go to near 100%, causing a problem. In my experience, it is a rare house that has a dry enough on-ground slab to put on glue down or vapor retardent flooring without moisture buildup problems unless a full vapor barrier has been installed. However, if you told him you wanted X type of flooring, while it would be nice if he warned you it might not work, he has no legal obligation to warn you off. This has been long established in the courts going back to old English days of contractors working for the British Admiralty, where owners try to sue for a non-functional work product but if it comes back that the plans and specs called for that specific product, the contractor is entitled to assume that is what the owner wants and he and his architect/engineer has considered all the issues related to it, and the contractor is not responsible to correct the owner's misimpressions.The case I recall in law class was a British warship the contractor actually told the Navy rep that the design was topheavy, but he was ordered to build it. It sank on the initial cruise and the Navy tried to recover payment, but the courts held the contractor was not obligated for the failings of the owner's design. If the work being done is actually against code and the contractor recognizes that fact, that is a different issue, as a contractor is not supposed to violate code without a waiver from the local code authority.

2) if your water table is high enough that the capillary zone (the 1-6 foot damp zone above the water table) reaches up to the slab from below, then short of taking out the slab and rebuilding with a fully waterproof design, you are unlikely to solve the moisture problem if it is from water wicking up to the bottom of the slab.

3) if the issue is "damp feet" because of surface runoff and seepage going in under the slab from outside the house, that MIGHT be solveable with diversion of surface waters and/or a french drain along the outside of the footer, but that depends on soil permeability and clay content. A footer drain is usually not significantly BELOW the slab elevation if at all (usually at about slab level), so that will not eliminate the moisture problem if you have free water outside the foundation wall, especially if the slab was not built as a "drained slab" in the first place, which most are not. In fact, some people have INCREASED slab moisture problems after installing a french drain to correct foundation wall dampness issues, because if not significantly sloped and installed at the very bottom of the trench it can concentrate standing water at the base of the footer, which then seeps right under to the underside of the slab.

4) For a floor on an existing dampish slab, you have only three viable solutions that are likely to work - but never guaranteed: use an open-weave carpet over padding that allows moisture to freely pass through, go with a grouted tile or stone floor or finished concrete surface which is not significantly affected by the moisture and lets it pass through and evaporate, or seal it with a penetrating sealer (which involves forced drying out of the surface first) then putting down a true vapor barrier like 6 mil poly sealed at all seams and around the edges, covered with a ventilated firring space or ventilated pad and floating flooring.

5) Sounds like you had a glued-down engineered wood floor installed - which to me is an invitation to problems, because of the changes in length of the wood with moisture changes will commonly cause buckling of the wood, especially on concrete or basement floors. Why they did not put down a vapor barrier and install a floating floor beats me - that would be the standard procedure for this location.

6) Solution - no mater what, I think it has to come up and be thoroughly dried out - which might or might not allow reclaiming some of the material. Then solve the mositure proboem is the slab is actually wet rather than trapping of moisture in the wood being the problem, then either install it correctly or change flooring type and maybe reuse the engineered wood somewhere else.

Answered 6 years ago by LCD

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