How to Gelcoat a Boat Hull

When a boat hull is made of fiberglass, the final outer layer consists of a gelcoat. Boatbuilders either spray on or paint on the gelcoat skin to protect the fiberglass underneath from water exposure. The application of the gelcoat seals the fiberglass and creates a sheen on the hull, giving it a glossy effect. To repair or apply gelcoat, the boat needs to be taken out of the water and dried. Additionally, the gelcoat needs reapplication over time as water and the elements eat away at it.

Things You'll Need

  • Rags
  • Sander
  • Sandpaper
  • Acetone
  • Chemical hardener
  • Gelcoat resin
  • Mixing bucket
  • Mixing stick
  • Sprayer gun and container
  • Paint suit
  • Gloves
  • Goggles
  • Respirator
  • Soap and water
  • Naphtha
  • Foam pad
  • Fine rubbing compound
  • Swirling remover tool
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Instructions

  1. Preparation and Mixture

    • 1

      Move the boat out of the water and onto a dry location. Wipe down the boat hull with rags. Sand off any prior gelcoat, barnacles or residue from the surface with a sander and sandpaper. Apply an acetone rinse to the sanded surface and then let the hull dry.

    • 2

      Mix 40 cc’s of chemical hardener per gallon of gelcoat resin in a bucket. Combine the chemicals using a mixing stick. Add in 10 percent to 15 percent of acetone, depending on how much gelcoat you started with. This acts as a thinner. Continue mixing until the mixture starts to thicken.

    • 3

      Place the mixture into a sprayer container. Close the container lid. Put on a paint suit, gloves and safety googles. Also put on a respirator to protect your lungs from the mixture fumes and overspray.

    Application

    • 4

      Spray the gelcoat onto the fiberglass hull using multiple coats and a paint sprayer after filling up the sprayer with the part 1 mixture. Spray the gelcoat mixture evenly so you don’t apply too much in one spot at the same time. Continue spraying until you have applied at least three even coats across the hull and developed a thickness measuring 30 mm. Let it dry for a couple of hours between each coat.

    • 5

      Wait two days to go after the final coat begins to dry. Begin sanding the gelcoat with a 320 grit sandpaper. Apply the sanding with water so you can wash off the residue and reduce the friction. Use an automated sander to make the job easier over a large area.

    • 6

      Give the sanded gelcoat surface a wash with a soap and water. Wipe it with naphtha.

    • 7

      Sand the gelcoat again with a 1,000 grit sandpaper and sander. Keep sanding until the original, harder sandings have smoothed out to a clean surface. Rinse off the surface again with running water. Let it dry.

    • 8

      Use a foam pad to apply a fine rubbing compound over the gelcoat surface. Remove the compound with a swirling remover tool and another disposable foam pad. Continue the remover application until the surface appears glossy from the waxing.