How to Repair a Painted Fiberglass Hull of a Dinghy

A repaired dinghy is a happy dinghy.

Fiberglass dinghies may sustain damage from impact with underwater rocks, pier supports or other collisions. If your boat is damaged you have two options: throw it away or fix it. If you choose to fix it, you will find that the process is not nearly as difficult as it may at first appear. You can create a fiberglass patch out of materials purchased at your local hardware store.

Things You'll Need

• Scissors
• Jigsaw
• Dewaxing solvent
• Scrub brush
• Grinder
• Paint brushes
• Acetone
• Rag
• Paste wax
• Plastic sheet
• Duct tape
• Fiberglass mat and cloth
• Fiberglass resin and catalyst
• Gelcoat and catalyst (optional)
• Disposable buckets
• Resin roller or squeegee
• Electric sander and various grits of sandpaper
• Paint matching the hull
• Wax (optional)
• Polish (optional)

Instructions

1. Remove the boat from the water and allow it to dry.

2. Tap the area around the damage with a hard object in order to test the integrity of the fiberglass. Good fiberglass makes a sharp tapping sound, while damaged and delaminated fiberglass sounds dull.

3. Cut out the damaged fiberglass with a jigsaw. Keep the hole as circular as possible for the maximum retention of strength.

4. Wash the inner hull with a dewaxing solvent. You will be repairing the hull from the inside, so you want the best possible bond.

5. Grind the area around the hole on the inside of the hull until it is a bit deeper than the surface. This ensures a good bond with the new fiberglass, as well as allowing you to create a patch that is flush with the hull.

6. Remove any dust from the ground area and wash it with acetone and a rag.

7. Apply a thick coat of paste wax to the outer hull around the hole to prevent any resin from sticking.

8. Tape a piece of cardboard to the outer hull over the hole. It will form a backing on which to build a patch.

9. Wax the inner surface of the cardboard.

10. Cut several layers of fiberglass cloth and mat to fit the ground area. You should have one layer for every 1/32-inch of hull thickness. Cut a few extra layers of mat.

11. Mix a batch of gelcoat (thick resin) with catalyst according to the instructions on the packaging. If the hole is below the waterline, skip this step and use epoxy resin for the repair instead of polyester resin.

12. Brush a layer of gelcoat onto the waxed surface of the cardboard. This will give you a smooth outer surface that is flush with the outer hull.

13. Allow the gelcoat to fully cure. Once it has hardened you are ready for the next step.

14. Mix a batch of fiberglass resin and catalyst.

15. Brush a coat of catalyzed resin onto the gelcoat.

16. Apply a piece of fiberglass mat into the resin. Mat sands much smoother than cloth and will be used for the outer layers on both sides of the patch.

17. Tap more resin into the fiberglass with the paint brush, soaking it completely and forcing out any air bubbles.

18. Add two more layers of fiberglass mat and resin.

19. Build up the bulk of the patch by alternating layers of cloth and mat until the hole has been filled.

20. Finish the patch with three layers of fiberglass mat.

21. Allow the fiberglass to fully cure for several hours.

22. Remove the cardboard and fill in any imperfections to the outer surface with more gelcoat. Allow it to fully cure.

23. Sand both sides of the patch smooth, starting with coarse sandpaper and moving to finer and finer grits.

24. Paint the hull to match the existing paint job, feathering the edges out into the existing paint.

25. If desired, wax and polish the boat.

Tips & Warnings

• Use proper ventilation when working with fiberglass resin.

• Wear protective gloves, goggles and a dust mask when working with fiberglass.

References

• Boat U.S.: Fiberglass Repair
• Serious Explorations: Step by Step Fiberglass