- Vapor barriers are placed between the soil and the concrete at the time of construction. These materials retard moisture and prevent it from migrating through the concrete floor of your garage, where it may cause high humidity, structural damage and mold growth. Vapor barriers are typically placed over gravel, although sometimes they are under a layer of sand or crushed rock, and must touch the perimeter wall to provide adequate protection from moisture.
- Polyethylene sheeting can create the vapor barrier. The Environmental Protection Agency recommends using 6-mil polyethylene sheeting for maximum moisture control. This sheeting must not have gaps in coverage and should be taped together so moisture cannot come through. Vapor barriers are especially important in hot, humid climates and in very cold climates.
- Placing a vapor barrier underneath your concrete garage floor helps slow the rate at which moisture migrates through the soil. Sealing the surface of the concrete will not prevent moisture. When moisture is seeping through into your garage, the humidity becomes higher, and mold may begin to grow. Mold decays the material it is growing on, causing costly repairs. People living in homes with mold growth often suffer adverse health effects such as sneezing, congestion, wheezing and hives.
- The soil must be level before you put vapor barriers in place. You add gravel to a depth of 4 inches. Place polyethylene sheeting over the gravel until it touches the perimeter wall. Secure the sheeting to the wall with tape or caulk. You pour the concrete floor over the sheeting for optimal moisture control.