how to repair fiberglass boat floor
Check for soft areas where the floor sags when you stand on it. If there is one, cut a large inspection hole there; you can close it later with a piece of plywood if you've found the rest of the floor in good order and the bottom is dry. If it is wet and moldy down there, you have no option but to remove the whole floor. CDK, Aug 8, 2011
Once the deck is in place, attach the sheets together with screws so it will all be in one piece. As with the stringers, apply fiberglass matting all over the deck to make it water-resistant. Finally, fasten the deck with some screws at the boat edges and apply a sealant so that no water will penetrate it.
Use the cordless drill and start stainless steel wood screws in the pilot holes on the floor. Apply marine adhesive to the face of a 4 inch wide piece. Hold the piece in place against the underside of the boat floor so that it spans the length of one side of the opening with 2 inches of the long edge exposed.
Spread resin on the cloth then spread the smallest fiberglass mat over the cloth. Use an air roller over the patch to get rid of air bubbles. Apply resin and attach the next bigger sized mat onto the cloth. Spread some more resin. Continue to work this way until the fiberglass is flush with the floor.