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Question DetailsAsked on 10/3/2013

What could cause water and mold on top of a slab foundation?

The water and mold were detected during the process of installing a new floor. A ten-year-old floating cork floor, then a plastic waterproofing sheet were removed. The cork glue-down floor that served as underlayment under the plastic sheet was saturated and moldy. The underlayment was removed from the house immediately, and the foundation and remaining glue are covered in mold. We are currently awaiting a call from a water remediation company. They are meant to provide us with contact information for a CHI. Per my insurance adjuster, a CHI is the person who can diagnose the cause of the mold and prevent it from recurring, and I contact the CHI directly (not through my insurance company) because my mold policy is in Texas. Thank you in advance.

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1 Answer


I am surprised they sent you to a CHI (Certified Home Inspector) - usually a CMI (Certified Mold Inspector) would do the evalauation and determine what is needed. You might double check with them to be sure you get the right person.

Diagnosing this one is incredibly simple - someone got lazy. When they saw the glu-down cork flooring (which might have already been getting moldy) they threw a plastic sheet over it and put the floating cork on top. The problem is, concrete is really quite a good transmitted of water vapor - is does not pass a lot of water through it, but it wicks water quite nicely, so moisture from the slab got into the glue-down cork, which had previously then released that vapor to the air. Put a plastic sheet over it, and presto - you have a mold and mushroom farm. The mushrooms would have died off pretty quick due to lack of air, but the plastic sheeting kept the moisture in the underlying cork layer and caused mold growth - I would be surprised if there was not quite a lot of fungus growth too, as it LOVES cork, which is why cork is NOT recommended for damp areas.

Two other possibilities for the water source is that groundwater came up along the edge of the slab or through the foundation wall and actually overflowed the slab and caused the problem, or that you have a pipe leak somewhere - same result, slightly different pathway.

Solution - solve the water source, strip everything off the slab, HEAVILY disinfect with antifungal solution, then soak in bleach for several days (usually done with a saturated thin cloth under a thin visqueen and a large fan exhausting to the outside to cut down fumes), then wash the floor and let dry thoroughly, seal it, then proceed with vapor barrier and flooring installation. Obviously, if the groundwater is coming through the foundation walls or lies close enough under the slab that it caused this once, it is likely to happen again unless the foundation wall is sealed (if that is the source) or a perimeter drain and sump pump is put in. If the water came from a pipe leak, then could of course be a decade or more before it happens again.

I would not be in the least surprised if you find out that your insurance will NOT cover this - if the underlying cork was truly saturated (as opposed to thoroughly surface damp), then likely cause is groundwater (unless a pipe break), which is almost never covered by a homeowners policy. I suspect this is why they sent you to a CHI/CHM instead of them hiring on - tht they expect to not have to cover any of the loss.

Answered 6 years ago by LCD

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