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post #1 of 6 Old 05-01-2013 Thread Starter
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Epoxy vs Polyester Resin for Repairs

I am thinking about repairing the cockpit sole of my boat. It has major moisture issues and I am trying to figure out the difference between using Epoxy or Polyester fiberglass resin to wet out the fiberglass after the new balsa core is set in place. I am wondering what experiences others have had with either product.

I know that epoxy will most likely be more ridgid but I believe it was originally polyester so would the epoxy be overkill?

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post #2 of 6 Old 05-01-2013
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Re: Epoxy vs Polyester Resin for Repairs

Epoksy is much better for repairs. Poliester does not adhere well to already cured poliester.
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Re: Epoxy vs Polyester Resin for Repairs

When resins are laid up originally they form a 'chemical' bond. When things are 'fibreglassed in' after the fact you're dealing with what is called a secondary bond, which is really the ability to 'stick' to the substrate. Epoxy has a much stronger secondary bond over polyester as celenoglu indicated, and is therefore much preferred for after-the-fact repairs, esp when the original polyester is no longer 'green' or fresh.

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Re: Epoxy vs Polyester Resin for Repairs

Epoxy sticks well to polyester, polyester wont stick to epoxy. UV breaks down epoxy, so a urethane topcoat would be a good idea.
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Re: Epoxy vs Polyester Resin for Repairs

When i refit Seafever the 1970 polyester hull was still rock-solid BUT i am still amazed at how easy it was to peel OFF a LOT of the secondary tabbing work holding in bulkheads





Everything in the engine are that was taped pretty much pulled off by hand and i feel much better with the replacement epoxy tabbing

1970 Cal 29 Sea Fever

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post #6 of 6 Old 05-01-2013
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Re: Epoxy vs Polyester Resin for Repairs

Almost all professionals will use polyester. The myth about secondary bonding is based on poor repair jobs and lack of proper preparation in production boat building. Properly done a polyester repair is just fine. it has been shown that epoxy is only 10% stronger than a epoxy repair. I would recommend polyester for your repair but I know I am in a minority here because WEST has done such a good job of marketing that most amateurs think it is the only thing to use. If you do a good job of surface preparation which you should do with either resin you will get good results. your boat is built of polyester it only makes sense to repair it with polyester. Mixing materials is never a good idea. I have been building and repairing boats for 40 years now and if it were my boat I would use polyester. Epoxy is difficult to work with and has poor wetout properties costs 5 times as much. Getting full strength from epoxy requires a good skill level proper temperature and use of the right fabrics. you cannot use fabrics designed for polyester with epoxy and get good results

Capt. Wayne Canning, AMS

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