Use 3M Marine Adhesive Sealant 5200 to seal joints and boat hardware. Our high performance polyurethane sealant chemically reacts with moisture to deliver strong, flexible bonds, retaining its strength above or below the waterline. Our sealant has excellent adhesion to wood, gelcoat, and fiberglass, forming a watertight, weather resistant seal which becomes tack-free in 48 hours, and cures completely 5 to 7 days. Its flexibility also allows for dissipation of stress caused by shock, vibration, swelling or shrinking.