No Plastic Under Concrete Slab

Thick concrete samples having a w c 0 50 and sealed from below required 82 days for the vapor emission rate to reach 3 0.

No plastic under concrete slab. Recently though research has shown that the old traditional layer of 6 mil visqueen polyethylene plastic under the slab is seldom effective for two main reasons. This water can take literally years to dry out through the top of the concrete slab. This plastic sheet is in direct contact with the concrete as it should be in a rational world. The reason is that the vapour barrier stops moisture from the wet concrete escaping into the ground under the concrete.

Or just use the plastic sheet to do both be the vapor barrier and the capillary break. The other contractor says no way no plastic holds the water in the concrete during the drying process and can leave webbing like visual affect in finish of concrete. It then reacts with the cement and soaks back into the concrete within an hour or two helping to complete the curing process. Why do concrete slabs need black plastic membranes under them.

What is a vapour barrier under a concrete slab and why do you need one. The rate that moisture escapes from a slab depends on the concrete w c the density of the finish the ambient conditions above the slab and the moisture below the slab. One contractor says to put plastic under the concrete it prevents moisture from coming up into the concrete. One laboratory drying study indicated that 4 in.

So why not just use plastic and not stones. If the plastic is right under the concrete the bleed water is forced to rise to the surface. Almost everywhere except california that slabs are placed on the ground a plastic sheet a vapor barrier is located directly under the concrete slab and on top of the ground photograph 1. In fact most professional shed slab builders will install a polyethylene membrane under a shed concrete slab even if it is not specified.

A concrete vapor barrier is simply a sheet of polyethylene plastic visqueen placed directly on top of the sub grade before the concrete floor or slab is poured to help keep moisture from the soil from passing up through the concrete.