F Ball - Stopgap F77 (14kg) High Performance Waterproof Surface Membrane STOPGAP F77 is a solvent free two part epoxy resin system which cures to provide a waterproof surface membrane. STOPGAP F77 impedes the passage of residual construction moisture and rising damp from affecting subsequent floorcovering installations, therefore allowing early installation of floorcoverings in fast track building programmes. STOPGAP F77 is pigmented black to allow the user to visually control coverage uniformity. It can be used to isolate residual construction moisture where relative humidity values are up to 98%. STOPGAP F77 can be applied direct over underfloor heating screeds using a coverage of 1.8m²/kg where readings are up to 90% RH.