What are Vapor Barriers?
All of the problems associated with moisture vapor movement in a concrete slab will go away in time as the slab dries, as long as there is no source of additional water into the slab. Since the most common source is moisture in the ground beneath the slab, the solution is to completely take the ground out of the equation, by sealing the bottom of the slab. The best way to accomplish that is with a vapor barrier under the slab. Vapor retarders have been used since the 1950s. 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: • Although it may seem water-tight, this grade of material allows a lot of water vapor to pass through. • 6-mil plastic often gets damaged during placement of reinforcement and concrete, creating holes that can let a considerable amount of water vapor into the slab.
