How to Gel Coat Boat Hulls

Written by will charpentier
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How to Gel Coat Boat Hulls
Scratched gel coat is an appearance, not performance, item. (boat image by Alexandru Buzatu from

The clear, shiny gel coat surface on your boat is fragile and easily scratched. You can make small repairs--renewing the gel coat on the whole hull of a boat is a job for professionals--during your winter lay up or preseason fitting out work using a gel coat repair kit. These kits contain the basic materials--the gel coat paste and catalyst--you'll need for the repair and are available at most marine suppliers.

Skill level:

Things you need

  • Gel coat repair kit
  • Paint scraper
  • Screwdriver
  • Flexible plastic spreader
  • Plastic film or sandwich bag
  • Tape
  • Sandpaper: 120 grit, 220 grit, 400 grit, 600 grit
  • Rubbing compound
  • Paint roller
  • Mild soap
  • Epoxy primer
  • Two-part linear polyurethane paint

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  1. 1

    Open the gel coat repair kit, add the colouring to the gel coat paste, and then add the catalyst to the paste according to the manufacturer's instructions.

  2. 2

    Pull the corner of the blade of a paint scraper or a screwdriver through the scratch, enlarging the scratch to a wider, if not deeper, "v" shape.

  3. 3

    Use a flexible plastic spreader to work the paste into the scratch. Continue until the surface of the gel coat paste bulges above the surface slightly, to compensate for shrinkage as the gel coat cures.

  4. 4

    Lay a sheet of plastic film over the repair. Tape one edge of the plastic to the undamaged part of the hull, smooth the plastic out over the gel coat and tape down the sides of the plastic to seal out air, since gel coat won't cure when exposed to air. If a plastic sheet isn't supplied with the gel coat repair kit, a sandwich bag works well. Wait 24 hours.

  5. 5

    Peel the plastic away. Sand the surface with 120 grit sandpaper until the surface is flush. Wet sand the area with 220 grit sandpaper, using a circular motion until you can't feel a ridge between the old gel coat and the new. Switch to 400 grit sandpaper and continue wet sanding until the repaired surface looks uniformly smooth, then switch to 600 grit sandpaper to finish feathering the repair into the undamaged surface. Use rubbing compound to finish polishing the area to a gloss, then wax the area.

Tips and warnings

  • If your hull looks like it's "spider webbed" with hairline cracks, that's called "crazing." Sand the surface and wash it down with mild soap and water. Experts, such as Don Casey of the Boat Owners Association of the United States, recommend using a paint roller to apply two coats of epoxy primer followed by two coats of two-part linear polyurethane. As Casey says, "The epoxy fills and seals the cracks, and the polyurethane restores the colour and gloss."
  • This work should be done in a well-ventilated area.

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