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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:

  • Stir Stick
  • Mekp (Hardener)
  • Spray Gun
  • Styrene
  • Acetone
  • Fiberglass Gel Coat

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.


  • Always wear a respirator when working with fiberglass materials.
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