epoxy or polyester resin

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scottnewcombe

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What's the difference?

I have used epoxy resin (West I believe) for bonding up plywood panels and the likes on some small repairs. My brother-in-law was replacing some that he had used but came back with a big tub of polyester resin instead.

What would be the practical uses of each. Not intending laying up huge amounts of fibreglass. Probably sealing up ply panels for deck hatches and the likes.

I'm quite sure the more experienced among you will have the definative answer

Thanks

Scott

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for bonding to plywood, only epoxy will do as it is an adhesive while polyester is only a plastic. polyester is much cheaper and is preferable for making components and repairs to grp structures. both will bond to existing grp as long as it is well abraded, there are mixed views on this but my professional advisor says polyester makes a slightly stronder bond.

epoxy is more toxic and users can develop severe allergic reactions.

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Thanks guys

I have looked at the west systems site before. Quite informative. This kind of information is what promted me to buy epoxy the first time round.

So polyester more suited to GRP repairs, not bonding /coating /fairing etc.


Cheers

Scott

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In short when using wood Epoxy bonds too! (becomes part of) polyester sticks too (mechanical grip) Epoxy gives a much better and stronger join. Both have there place but with wood its epoxy every time?

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I wish I'd been born rich instead of good looking ?
 
As I understand it, the only real merit of poly resins is their cheapness. That is certainly why they are used in mass boat building. They are less good adhesives than epoxy, and new poly adheres not very well to old cured poly. Which is why you need to abrade the surface well and to taper the join so that there is a good surface area of bond. To add to the disadvantages, the catalyst ratio is small which can make mixing thoroughly that bit more difficult and they are chemically prone to osmosis. Its inherent in the nature of the resin.

Epoxy is a much better adhesive, the mixing ratio is easier, but the cost is higher and epoxies also soften under heat. Worst of all, lots of people can become sensitised to epoxy and allergic to it. So its not an easy material for bulk boat building, though it was interesting to see from a brochure this week that Tartan yachts of the US actually do do this. Oh, and you cant get osmosis with epoxy. And its exceedingly sticky when liquid so ita almost impossible to make a good job of epoxy and chopped strand mat - in my personal experience that is!

You should make sure you use the correct glass fibre materials. Glass cloth for poly isnt usually suitable for epoxy.

<hr width=100% size=1>this post is a personal opinion, and you should not base your actions on it.
 
Thanks again

I have showed my brother in law these posts and we are going shopping again.

We will probably keep the polyester in case!


Scott

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