How to Thin Polyester Fiberglass Resin With Acetone

by Jay Kurz
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Polyester resin is the most commonly used type of resin and the cheapest. Resin is a thick fiberglass liquid that when mixed with 2 percent catalyst becomes a solid. You can use more or less catalyst to change the amount of time it takes to harden but don't use much less than 2 percent. Polyester resin will bond to almost any surface including metal, wood, foam, plastic and ceramic. When used on porous materials like wood, the resin will not penetrate the wood and form a strong bond unless it's thinned out. Polyester resin also is used for gel coat, which is fiberglass paint that has to be thinned for spray application. Polyester resin can be thinned out using no more than 10 percent acetone. Any more and the fiberglass will not completely harden.

Step 1

Put on a respirator and a pair of rubber gloves. Fill a small bucket 3/4 of the way full with polyester resin using a measuring cup. Keep track of the amount of resin you poured into the bucket.

Step 2

Add 10 percent acetone to the resin or 10 parts resin to 1 part acetone. Thoroughly stir the acetone into the resin until it completely mixes together.

Step 3

Add 2 percent catalyst to the bucket of thinned resin and thoroughly stir it together with a stir stick. The fiberglass will harden within 30 minutes after the catalyst is added.

Step 4

Apply the resin to the surface of the wood or other porous material using a felt roller. Roll the resin on as evenly as possible in a heavy coat and let the resin harden.

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