How to Repair Fiberglass Boat Sterns

During boating season, pulling into the fuel dock can be like participating in a waterborne demolition derby. Sometimes, just sitting in the slip can leave you with a damaged fiberglass boat. The most damaging hit your boat can sustain is being hit in the stern because, unlike the bow or the sides, the stern is wide and flat. A collision to your boat's stern can cause major cosmetic damage. You can usually repair the damage yourself.

Things You'll Need

• Resin-based putty (available from boat dealers)
• A wide-blade putty knife
• A small-blade putty knife
• Palm sander and #000 grit sanding disks
• #00 and #000 grit sandpaper sheets
• 2-part Epoxy (resin and hardener)
• Acrylic epoxy paint to match the color of your boat's stern
• Gel coat (available from your boat dealer)
• Several paint brushes
• Short-nap paint roller
• Fiberglass cloth

Instructions

1. Fill in any depressions, cracks and holes in the stern with the resin-based putty. Work the putty into the depths of the damaged areas thoroughly with the small-blade putty knife; use the large-blade putty knife to fill in the rest of the damage with just a bit more putty than you think you'll need. The surface should be slightly humped, if you have used enough; it will shrink as it cures and you'll sand that down to a fine level surface. Let the putty cure for at least 24 hours before moving on to the next step.

2. Use the palm sander and #00 grit sandpaper to sand the putty down until it is level with the surrounding surfaces. If there are any voids in the surface of the putty after sanding, fill the voids with putty, wait 24 more hours and sand once more. Cut the fiberglass cloth to form patches to fit over the repaired areas. Use more than one patch to cover an area if necessary.

3. Mix the epoxy resin and hardener according to the directions for the product. Apply a thin coat of epoxy to the areas you sanded, using the paint roller. A roller with a "short-nap" won't leave acrylic fibers in the resin, unlike a longer-nap roller, and will give a more workable coat. Immediately apply the fiberglass cloth patches to the repaired areas, it will bond with the epoxy you applied.

4. Allow 24 hours for the epoxy to harden and make sure that the fiberglass bonded completely with the epoxy. Use the palm sander and #000 grit sandpaper to sand the fiberglass surface down until it is even with the rest of the surface of the stern. Wipe the sanded areas with a dry cloth to remove excess dust from sanding and paint with the acrylic epoxy paint.

5. Allow the paint to dry, then cover the painted fiberglass with gel coat.

Tips & Warnings

• Do not mix the epoxy resin and hardener until you are ready to use it. It will begin to dry as soon as it is mixed. If you have a large area to repair, or more than two small areas, mix the epoxy in multiple small batches.

• Mix and use the 2-part epoxy in a very well ventilated area, preferably outside.

References

• The Fiberglass Boat Repair Manual; Allan H. Vaitses, McGraw-Hill Professional, 1988

Resources

• Read this Article in Spanish
• The Fiberglass Boat Repair Manual