Grind out gelcoat blisters to create a beveled edge. If the area is wet, allow it to dry completely before making repairs. Clean the area with acetone, then fill the blister with TotalBoat Polyester Fairing Compound or TotalBoat Polyester Structural Marine Repair Putty. Once cured, sand the repair smooth with 80-grit sandpaper, wipe the surface clean with acetone, and apply gelcoat.