To install a polythene vapor barrier, choose the location for installation, measure the wall, cut the barrier to the appropriate size, roll it in place and staple to attach the barrier. Vapor barriers can be bought at most concrete supply stores.
Places where vapor barriers are installed include under the foundation, crawl spaces and attics. These areas are prone to humidity accumulating on the walls, which results in rot, mold and mildew. The growths can cause severe structural damage and health problems.
Next, prepare the work area ensuring that it is dry. Surfaces where water has already accumulated need to be cleaned and dried and any cracks or gaps filled with caulk before installing the vapor barrier.
Measure and mark the wall adding two inches one every side. Cut the vapor barrier to size and roll it onto the marked space, stapling it in place starting from the center and working outward on both sides. Smooth the plastic as you go along to avoid pleats and wrinkles. Add an extra layer of barrier on all joints.
Use insulation tape designed to be used with plastic vapor barriers to seal the barrier seams and ensure a waterproof seal. Carefully seal accidental tears or holes, and add an extra piece of tape on seams located at the joints.