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Q.Is there a spray-on waterproofing that's compatible with ICF foundations — that won't "melt" the polystyrene?

A.Bruce Richgels responds: When waterproofing ICFs, we use a spray-on polymer-modified membrane — either Tremco's Tuff-N-Dri or GMX's Ultra-Shield. The GMX product comes with a 20-year warranty, even when applied to ICFs. The key thing with ICFs is to use a water-based formulation rather than a solvent-based one, which would destroy the polystyrene.

Even though these coatings have the ability to withstand hydrostatic pressure, we always install a vertically stranded drainage board to protect the membrane during backfill. With ICFs, the R-value of the drainage board is not important, so the minimum thickness (typically 3/4 inch) can be used. As with any foundation drainage method, a perimeter drain tile in a bed of clean stone is also needed; usually, the coating manufacturer's warranty requires it.

Bruce Richgels is an account representative for Waterproofing Inc., a Minneapolis-based company specializing in foundation waterproofing.