SM Fast Primer is a fast-setting, water-based latex primer for Mapei self-adhesive membranes. It is non-hydrolyzable and pressure sensitive. SM Fast Primer dries quickly and dramatically increases the adhesion of Mapei membranes to approved and properly prepared substrates. It start off white but becomes transparent during drying, allowing the user to see the guidelines on the substrate even after application. Its quick drying, allowing membrane installation after about 15 minutes.