Vapor Barrier Below Concrete Slab

If you are going to seal an exterior slab find a sealer that transmits water vapor breathes.

Vapor barrier below concrete slab.

In general place the concrete slab directly on top of the vapor barrier with the subbase below. These 10 mil and 15 mil vapor barriers are very puncture resistant and will not break down over time creating a true moisture barrier between the sub grade and. A below slab vapor barrier can also help prevent sub slab radon ingress. New generation vapor barriers made from the highest grade virgin polyolefin resins have been developed that are considered true below slab vapor barriers or concrete vapor blockers.

One laboratory drying study indicated that 4 in. Stego wrap claims they have a virtually zero permeance under concrete slab vapor barrier. If heavy equipment will be operating on the vapor barrier or if the vapor barrier will be installed over an angular subbase a minimum of 15 mils is recommended. Aci 302 1 which is an american concrete institute standard for slab construction was modified in the early 2000 s to reflect the change in the placement of the vapor barrier directly below the concrete if a low permeable membrane flooring was to be installed.

Their use should be avoided where ground moisture conditions permit. Their 15 mil vapor barrier also controls radon gas is resistant to hot cold temperatures resistant to soil chemicals pollutants and like i said allows virtually zero water vapor transmission up through the slab. Most exterior slabs do not need a vapor barrier. If ground conditions require their use a 3 inch 75 millimeter layer of sand over the vapor barrier and under the concrete has been shown to reduce these problems.

Thin plastic like this is often called a vapor retarder meaning it slows the vapor down but doesn t stop it. For some tips on this see sullivan s corner. 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. When evaluating the performance qualities of vapor barriers as soil gas retarders be sure to check the radon diffusion coefficient of the material before you select it.

Chemical resistance consideration if a vapor barrier is being used under a slab to control vapors at a brownfields site the chemical resistance of the vapor barrier must be considered. Should you put a vapor barrier under concrete slabs. Vapor barriers aggravate the problems of plastic and shrinkage cracking. Many vapor barriers are synonymous with soil gas retarders in construction language.

A much better approach is a true vapor barrier with characteristics that conform to the requirements of astm e 1745 standard specification for water vapor retarders used in contact with soil or granular fill under concrete slabs.