Before we start construction for any basement project we lay dimpled PVC sheeting on top of the concrete slab. For carpet and laminate flooring the sheeting is installed loosely. For tile and hardwood 3/4" plywood must be installed on top of the sheeting and secured to the floor with masonry screws. The purpose of this dimpled PVC vapor barrier is to isolate the floor from the floor covering. Failure to do so will lead to mold growth. Condensation forms at the point where cold meets warm. The greater the temperature difference between the floor surface and the surrounding air the more condensation is created. The dimpled feature allows air to circulate under the floor covering and prevents any moisture from coming in contact with the floor coverings. Photo By Signature Spaces LLC