How to Wet-Sand Gelcoat

No matter how much care you take with your baby, a boat hull inevitably scratches from hitting winch handles, weights and other hard objects you may have trouble seeing under the water's surface. To properly fix cracks in your gelcoat, you'll need to apply a gelcoat paste and wet-sand the repaired area until it's smooth. This process can be time consuming, depending on how long you go between repairs.

Things You'll Need

  • Liquid dish soap
  • Water
  • Tack cloths
  • 2 bowls
  • Masking tape
  • Screwdriver
  • Gelcoat paste kit
  • Putty knife
  • Plastic wrap
  • Sandpaper, 220-, 400- and 600-grit
  • Wood block
  • Marine wax
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Instructions

    • 1

      Mix two tablespoons of liquid dish soap with two gallons of warm water to create a cleaning solution. Wash the affected area of your boat hull to remove debris. Then allow the area to air dry.

    • 2

      Mark the borders of the repair area with masking tape, so you don't sand out of the area.

    • 3

      Run a screwdriver down the center of cracks to widen them. This ensures that the gelcoat paste bonds to the hull for a proper repair.

    • 4

      Mix your gelcoat paste with color pigments to match the shade of your boat's hull. Getting an exact color match is challenging even for professionals. Start with the white gelcoat paste, and all paint little by little. The color will change as the gelcoat hardens, so diagnose your color match from a hardened gel coat color test, not a wet one.

    • 5

      Cover the gelcoat paste with plastic wrap--it does not dry properly if exposed to air--and allow it to set up. Fill the chips in your hull with gelcoat paste. Allow the gelcoat paste to set up, following the manufacturer's recommended wait time.

    • 6

      Fill a bowl with cool water. Place a 220-grit sheet of wet sandpaper in the bucket.

    • 7

      Pull off the plastic wrap. Then remove the 220-grit wet sandpaper from your bucket of water and wrap it around a small block of wood. Draw the sandpaper across the hull from side to side. Work in long, lean strokes. Dip the sandpaper back in the water to remove gelcoat paste chips and keep it wet.

    • 8

      Work with the 220-grit sandpaper until you cannot detect the change in surface level with your finger, so the gelcoat appears smooth. Then switch to 400-grit wet sandpaper and sand with the same technique. Use 400-grit until the repaired area looks even in texture, then switch to 600-grit for an even finer finish.

    • 9

      Dip a tack cloth in a tub of marine wax, then cover the repaired area with wax. Apply just enough wax to coat, working the polish into the boat hull with circular motions. Remove the masking tape to finish the job.