“If you are installing hardwood flooring over concrete, you will need a floor vapor barrier between the concrete and the wood. Indeed, you will likely find this is part of the warranty coverage for this flooring. If you install the hardwood directly on the concrete, you will find that moisture from the soil will evaporate through the concrete and penetrate the wood, causing warping or mold. It pays, then, to follow the proper instructions and invest in a floor vapor barrier. Vapor retarded paint, usually white, costs $20 to $40 per gallon. One gallon will give you nearly two coats of protection. If you use 8 millimeter plastic sheeting, which can cost from 25-cents to $2.50 per square foot, basing the cost on a 12 by 12-foot room, the cost will range between $36 and $215.”

article courtesy of doityourself.com