On Sep 12, 4:57 pm, "David Murray" wrote:
Hi there.
I have a small (14 foot) grp boat which needs some repair work done to the
hull and cuddy.
My question is which type of resin should I use for the repair - epoxy or
polyester resin?
I have a feeling epoxy is best for marine applications but just want to
check.
Please advise
Thanks
Davy M.

Polyester will do fine. I was looking at some 20-year old Abacores
this summer at a sailing club I used to belong to when the boats were
new. These are club boats used in training and racing so they get a
lot of abuse. The polyester repairs are all holding up fine.

Unless you buy epoxy in 55 gal drums and can get it cheap. In small
lots it's still pretty expensive. about twice the cost of polyester
around here. Or if you already have some epoxy on hand you want to use
up.

Polyester is more brittle and less adhesive but it's good on a ridgid
surface which is clean and pourous, which old sanded polyester is.

Epoxy is a great waterproof glue, and the cured resin is stronger and
more flexible than polyester. Also epoxy molecules are similar to the
cellualr structure of wood so it cures right into the wood for
excellent bonding.

Polyester is easier to mix and more forgiving. If you don't mix in
enough hardener you can mix up more and spread it on and the hardener
will migrate into the uncured resin. Epoxy has to be mixed right the
first time. Some people develop an allergy to the hardener used in
epoxy and have to stop using it. Epoxy can go on over polyester, but
polyester can't go on over epoxy, so once you switch to epoxy you
can't go back to polyester where you've made repairs.

Finally, most of what you read in this newsgoup about polyester is
boatbuilder myth perpetrated in the past by sellers of epoxy desperate
to find some excuse for people to buy the more expensive resin, and
when it first came on the market is was more expensive than it is now.
It was a hard sell as anything but a great strong waterproof
adhesive.

I only use epoxy when I have to, and use polyester wherever I can.
But I do not, nor have I ever, worn a polyester leisure suit. That's
just going too far.