Patching Fiberglass

A well-applied fiberglass patch should be as durable as the original surface.

Fiberglass is commonly used for the bodies of boats and cars. Despite its durable nature, fiberglass may occasionally puncture, causing leaks and detracting from the vehicle's appearance. According to do-it-yourself author Don Casey you can repair a fiberglass hole with a strong, long-lasting patch given the appropriate supplies, careful preparation and meticulous application. If possible, fiberglass should be patched from the inside of a vehicle to reduce the patch's exposure to water and the elements.

Things You'll Need

• Wax removing solvent
• Dust mask
• Protective goggles
• Sander with 36-grit sanding disk
• Acetone
• Rag
• Paste wax
• Smooth plastic laminate or thin clear acrylic
• Polyvinyl alcohol mold release (PVA)
• Fiberglass fabric
• Polyester, vinylester or epoxy resin
• Laminating resin
• Methyl ethyl ketone peroxide (MEKP)
• Gelcoat matched to the fiberglass color
• Resin roller

Instructions

1. Wash the fiberglass surface around the puncture on both sides with wax removing solvent to promote adhesion of the patches.

2. Put on protective goggles and a dust mask to protect you while operating the sander.

3. Sand a 12 to 1 bevel around the hole's perimeter with a 36-grit sanding disc. When finished with the perimeter, sand a rectangular spot of the interior surface several inches beyond the bevel.

4. Wipe the target area with a rag soaked in acetone to clean the area and remove sanding dust.

5. Generously coat the surface around the hole, but not inside, with a layer of paste wax.

6. Cut a piece of plastic laminate or acrylic 1 foot bigger than the puncture. Apply paste wax to the back and spray it with PVA.

7. Tape the plastic or acrylic to the outside surface over the hole.

8. Measure the thickness of the fiberglass surface to determine how many layers of fiberglass fabric you need to repair. You will need one layer for each 1/32 inch. Cut enough fiberglass 1-½-ounce mat and 6-ounce fiberglass cloth for your needs; the first layer should be mat cut 1-inch larger than the hole. The second layer should also be mat, followed by alternating layers of cloth and mat. Each layer should be cut ½ -inch larger than the previous layer.

9. Mix resin with the MEKP catalyst and laminating resin according to package directions. Use polyester or vinylester resin, combined with laminating resin, for above-waterline repairs and epoxy resin for below-waterline repairs.

10. Spray or brush 20 mm. of gelcoat to the wax-coated back of the laminate or acrylic taped to the surface. Wait for the gelcoat to set.

11. Wet the gelcoat with resin. Apply the first three layers, one at a time, with a resin roller to remove bubbles and ensure a smooth application. Wait for the resin to harden, four more layers. Continue until all layers are applied.

12. Cut another piece of fiberglass mat in the shape of a rectangle. And a larger piece of fiberglass cloth and place them over the patch with the resin roller. Apply PVA if there is laminate resin to allow it to cure.

13. Remove the taped-on patch from the outside surface. Fix any imperfections with painted gelcoat. Sand and buff the area for a smooth surface.

References

• Boatus; Fiberglass Repair; Don Casey