Gelcoat thinner


Master Chief Petty Officer
May 4, 2015
I am planning on gelcoating my restored 2006 Baja islander. I started with filling surface dents and damaged fiberglass surfaces with fiberglass patch. Sanded and polished the fiberglass. Now I want to spay the repaired areas with the gel coat. I have a 27 gal compressor and a cheap hvlp spray gun from harbor freight. I need to thin the gelcoat before spraying it. From what I read about gelcoat thinners, I can buy a special resine styrene thinner,, but I also read I can use regular acetone. Also mixing gelcoat with hardener, instructions on the package i bought on ebay are missing but i have seen 12-18 drops of hardener on 1 ounce of resin. Higher amount in colder weather, lower in warmer. So, here are the questions, should I buy gelcoat thinner at a store or online, and if yes, which one, or should I use acetone? The other question, is there a more precise hardener resin mix recipe for gel coat?
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Mar 29, 2017
No gel coat is just fiberglass resin with a pigment use the normal mix ratio. Mix it lighter 1% give yourself working time and cleanup time or you will loose the gun when it kicks off hard fast. Longer working time lets it flow longer.

Use the correct thinner. My brother and i paint cars. And found that gel coat altho more labor intensive is much easier to get good results with. He talked to the tech guys and his baja you can't see where the patches are. I can get the name of the thinner if need be.

Just use the primer gun with the larger needle when spraying. Just ask or read the description if it is for primer. There are 2 needle sizes sold at harbor freight. One is for primer thicker like gel coat and the other is for thin like paint.
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Scott Danforth

Grumpy old guy who plays with boats
Jul 23, 2011
I used the duratec 904 gloss additive. it is made by Hawkeye products (Ondarvr) it makes the gel spray like paint. its both a thinner and a surfacing agent.

the Harbor Freight gun will not work, the tip is not large enough.

however the Vaper gun from Northern Tool or amazon with the 2.3 tip is fantastic (Same gun my local fiberglass place sells, however at 40% the price).

here is some light reading
I start spraying about page 12