Abstract: Methods of preventing intrusion of toxic vapor into a building's interior air space. Contaminants operative to diffuse through a building's foundation and contaminate a building's interior air space are first determined. Once identified, the building's foundation, typically formed of concrete, will first be prepared for surface treatment followed by an application of at least one coating of a material suitable for imparting chemical resistance in the concrete. Such material may include novolac, vinyl novolac and related resin-based epoxy coatings. Such coatings, once applied, provide a protective barrier from commonly encountered contaminants, including a wide variety of volatile organic compounds. Such coatings are further expected to last the life of the building, or until physical wear requires repair or replacement.