Same high-strength polyester resin that is used to build most boats. Use alone or with fiberglass tape, cloth or mat to repair damaged fiberglass boats, snowmobiles, jet skis, bathtubs and showers. Use as a sealer on damaged and rotted wood. Seals concrete. Use on large or small metal rust-outs. Joins most surfaces together while creating a strong and long lasting bond. Sandable in less than 2 hours. Compatible with all paints, including gel coat and marine paints. Waterproof. Includes liquid hardener.