How to Thin Gelcoat


Gel coat consists of fiberglass resin that is pigmented with color. Fiberglass resin is a thick liquid that requires a catalyst in order to become a solid. The consistency of gel coat is too thick to use in a regular spray gun, so in order to use it in a regular spray gun the gel coat will need to be thinned out using styrene. All the materials needed can be found at your local marine supply store.

Things You'll Need

  • Spray gun
  • Fiberglass gel coat
  • Styrene
  • Stir stick
  • MEKP (hardener)
  • Acetone
  • Pour the pre-matched gel coat into the cup of the spray gun. Fill it up ¾ full.

  • Add 1 part styrene to 10 parts gel coat, and stir the two together using a stir stick. The consistency of the gel coat should be around the same as car paint. Do not add more than 10% styrene to the gel coat or it might not harden.

  • Add the catalyst to the gel coat following the recommendations on the containers. Stir that in using a stir stick. Tighten the lid onto the spray gun cup.

  • Clean the spray gun thoroughly with acetone as soon as you're done spraying. The gel coat will harden up inside the gun if it's not cleaned after use.

Tips & Warnings

  • Always wear a respirator when working with fiberglass materials.

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