How to Repair Gelcoat


Gel coat is used as paint and as a protective layer for fiberglass. It consists of fiberglass resin pigmented to match any color. For outside applications, additives protect gel coat from UV rays. Gel coat often is cracked or fractured from general wear and tear. Fiberglass gel coat is generally easy to repair and refinish back to the original strength and shine. Gel coat is very thick and needs a gel coat spray gun for application. This and all the other supplies can be found at your local marine supply store.

Things You'll Need

  • Respirator
  • Palm sander
  • Fine-grit sandpaper
  • Fiberglass filler
  • Methyl ethyl ketone peroxide (hardener)
  • Small bucket
  • Stir stick
  • Putty knife
  • Rags
  • Acetone
  • Gel coat
  • Gel coat spray gun
  • Put on your respirator and sand any crack or fracture smooth using a palm sander and fine-grit sandpaper. If the cracks are deep, sand them until you are back to smooth fiberglass. If this causes a crater in the surface, gradually taper the edges of the crack.

  • Mix the fiberglass filler with the hardener as directed on the containers. Use a small bucket and a stir stick to thoroughly mix the filler. When the filler is one solid color, apply it to any uneven spots or indents in the surface. Use a putty knife to smooth the filler out. Make sure the filler is even with the surrounding fiberglass. Let dry until it's hard.

  • Sand the filler using the palm sander and fine-grit sandpaper. Thoroughly sand the filler until it is smooth and even with the rest of the surface.

  • Clean the surface using a rag and acetone. Remove any grease or dust that is on the surface. Grease can cause the gel coat to bubble up and not bond properly.

  • Add the gel coat and hardener to the gel coat gun as directed in the manual. The gel coat gun will internally mix the hardener with the gel coat while it's spraying.

  • Spray the first coat onto the repaired area or areas. Apply in a consistent and even heavy mist. The first coat will act as a base coat. Let the gel coat begin to cure and become tacky.

  • Apply the final coat of gel coat so that it solidly covers to the surface. Continue to spray as evenly as possible to avoid runs in the gel coat. Let the gel coat harden.

Tips & Warnings

  • Always wear a respirator when working with fiberglass.

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