"CARSON AXTELL" ) writes:
Hey guys/gals--

I hope I'm not bringing up a past controversy or rehashing old ground, but I
was wondering if anyone has any experience successfully combining the use of
epoxy (read "expensive") and polyester ("inexpensive") resins on the same
project? I have not yet found any literature on the subject elsewhere.

Yes, it's been discussed a few time before and caused at one expoxy
vendor to leave the newsgroup never to return.

I don't even use polyester laminate on my small plywood boats, just paint.
My boats are kept at home on dry land and sadly spend little actual time
in the water. Patin is fine. They are more expose to wind and rain in the
back yard than being immersed in water. Two are kept indoors hanging on
the wal of the garage.

The plywood panels are held together with screws and PL Premium
polyurethane adhesive, and then the exposed plywood edges are given two
coats of polyester applied with a toothpick to seal them. Polyester is
actually quite waterproof. It's only a problem blistering on large
all-fibreglass boats, mostly ones carelessly made by low paid workers who
drink to help put up with the nasty job of working day in and day out in
an atmophere of stinking sticky curing resin. That kind of think is
expensvie when the customer's boat starts to soak up water and
disintegrate, or the keel falls off, after a few seasons. Word gets around
and unfortunateley it's the polyester which gets the blame. Vendors of
epoxy love this sort of thing and are not shy about spreading the word.
Ity sure helps sell epoxy which is a hard sell otherwise, being the more
expensive resin.

I've also used polyester for butt joins in a small plywood hull without
any problems so far. I'll admit the joins are above the waterline, and
again, the boat spends most of it's time upside down in the back yard. If
polyester is used this way it should go on clean dry pourous plywood which
is not going to flex or come under a lot of twisting stress. It's a bit of
a judgement call. I don't see it as a problem on a small inexpensive boat
where epoxy would raise the cost significantly. On a large expensive
plywood boat I'd tend to use epoxy to eliminate the risk of the resin
coming away from the hull. But then for a large hull you can buy epoxy in
bulk and reduce the cost diffrence, and with all the expensive hardware,
power source, and appointments on a large hull, the resin becomes a much
smaller part of the overall cost of the boat.



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