Your resin and hardener could be off ratio Too much or too little hardener will affect the cure time and thoroughness of the cure. A. Remove the uncured epoxy. Do not apply additional material over non-curing epoxy. See Clean Up & Removing. B. Check that you’re using the correct number of pump strokes: Use equal strokes of epoxy resin and hardener. DO NOT add extra hardener for a faster epoxy cure! C. Check for correct pump (5:1 or 3:1 ratio) and pump group size (Group B epoxy resin and Group B epoxy hardener). D. Check epoxy pump ratio (see 300 Mini Pump Instructions). See Dispensing & Mixing. 2 . The temperature might be too low A. Allow epoxy extra curing time in cool weather. B. Apply heat to maintain the epoxy’s chemical reaction and speed the cure. C. Next time, use 205 Fast Hardener, designed to cure with epoxy resin at lower temperatures. D. See Cold-Temperature Bonding. 3 . The resin and hardener weren't blended thoroughly A. Remove the uncured epoxy. Do not apply additional material over non-curing epoxy. See Clean Up & Removing. B. Mix epoxy resin and hardener together thoroughly to avoid resin-rich and hardener-rich areas. See Dispensing & Mixing. C. Only add fillers or additives after epoxy resin and hardener have been thoroughly mixed. 4. Incompatible epoxy products were used A. Scrape away the uncured epoxy to remove it. Do not apply additional material over non-curing epoxy. See Clean Up & Removing. B. Check the compatibility of epoxy resin and hardener. Epoxy resin will not cure properly with other brands of epoxy hardener or with polyester catalysts.