R-Guard PorousPrep seals the dry, cut edges of gypsum wall boards exposed in rough openings for windows and doors. The sealed edge makes a perfect surface for easy application of R-Guard Joint & Seam Filler or R-Guard FastFlash®. PorousPrep brushes on easily and efficiently, and its glue-like viscosity reduces rundown and potential for spills. PorousPrep usually dries in 30 to 60 minutes when applied to dry surfaces. Use R-Guard PorousPrep as part of a continuous building-wide air barrier system, or to complement conventional waterproofing or air barrier components.