Polyurethane sealer. Tack tree in 48 hours. Cures in 5-7 days with no shrinkage. Extremely strong above or below waterline. Stays flexible. Bonds and seals fiberglass deck to fiberglass hull, wood to fiberglass. Easy to apply with manual caulking gun. Workable up to 4 hours after application. Won't sag or flow in vertical or horizontal Seams.