In the past decade, the use of spray-applied waterproofing membranes--materials tough enough to withstand hydrostatic pressure and elastic enough to bridge hairline cracks in a foundation wall--has helped foundation contractors boost the value of their services, as well as their bottom line.

The two main types of spray-applied waterproofing membranes for basement walls are solvent-based rubber and water-based polymer asphalt. Almost without exception, these products are marketed for new residential construction for the simple reason that just-built basement walls provide the easiest access and the most pristine surfaces for proper application. Still, contractors must properly prepare wall surfaces before membrane application. They also must apply the materials with care, especially volatile solvent-based products. Contractors and manufacturers alike advocate a two-coat application, which not only helps achieve a consistent, 60-mil coating thickness, it allows the first layer to dry or release its volatile compounds faster than if the entire thickness was applied at once.