Concrete floor problems
This typically results in moisture problems with floor coverings (Photograph 3 and Photograph 4).В The sand layer becomes saturated with water from wet curing (water added to the top of the slab leaks down into the sand layer through service penetrations) or from irrigation (water added to the ground at the building perimeter enters the sand layer from the side or from underneath) or from rain (see wet curing and irrigation).
The sand layer cannot dry downwards by vapor diffusion because of the plastic sheet-it is a vapor barrier after all. In fact that’s why we have it under the slab. We want a vapor barrier under the slab.** We want to prevent water vapor from coming up from the ground into the concrete slab.В But it works both ways”it prevents water vapor from going down as well. Bummer.