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.

On my first boat, I thought I'd use epoxy on the stitch'n'glue part of the
project, and then switch to polyester resin for the glass lamination of the
bottom of the hull. Since I didn't know what I was doing anyway, I bought a
1:1 resin/hardener type of epoxy (resin amber, hardener clear) that comes in
quart bottles in some hardware stores, which worked fine for gluing and
taping the joinery. But then, when I used the polyester resin to glass the
bottom, some kind of reaction occurred with the epoxy --even after several
days, the mating surface between the two resins had the consistency of a
runny gel that wouldn't harden. (To the best of my recollection, the epoxy
had already stood for several days in warm daytime/cool nighttime No. Calif.
tempertures of 80F+ to 50F+ and low humidity of 40% prior to the application
of the polyester resin, so it should have been well cured, or at least set.)

(The question of whether to use polyester resin at all on a plywood boat is
another matter and has yet to be decided, since I understand that polyester
resin, even when fully cured, is not as impervious to moisture as epoxy. On
the otherhand, it doesn't seem to be as affected by UV rays as epoxy,
either, and since I don't intend to leave the boat in the water, moisture
may not be the bigger problem...)

Any knowledgeable insight or advice on the subject would be appreciated.

Thanks,
Carson

PS: The solution to the gel problem was to strip the hull to bare plywood
where possible & start all over using only epoxy--not an experience worth
repeating... Fortunately, the project was just a D4--another testamonial to
the wisdom of making your first boatbuilding project a small one...;}

"...I have not yet found any literature on the subject elsewhere."

Fiberglass Boat Building for Amateurs / Ken Hankinson / 1982. Chapter
6, page 35.

Fiberglass Boats / Hugo Du Plessis / 1996. Chapter 2, page 17.

MW

Thanks for the references, Mike; I'll look them up. And thanks to everyone
else for the input on the compatibility question--seems pretty clear that
polyester resin laminations are probably best left to surfboards and other
less expensive craft that don't get stressed much, are easily replaced, and
stored out of the water whenever they're not being used...at least as far as
laminating wood goes. Full GRP hulls are presumably another matter
entirely.

Carson


wrote in message
oups.com...
"...I have not yet found any literature on the subject elsewhere."

Fiberglass Boat Building for Amateurs / Ken Hankinson / 1982. Chapter
6, page 35.

Fiberglass Boats / Hugo Du Plessis / 1996. Chapter 2, page 17.

MW

Hi, conventional wisdom has it that one cannot apply polyester resin on top
of (cured) epoxy. The amine in the epoxy does not allow for even a partial
cure of the polyester resin. BUT, I know of one boat yard that has used
polyester over epoxy with no problems. I got a blank stare when I asked
about it. I dunno, sometimes you get lucky.
Epoxy should stick and cure over cured polyester so if you really want to
mix and match the two, you may have to plan your build suchly.

Cheers,
Arnold


"CARSON AXTELL" wrote in message
news:2XEBe.22734$O56.21074@trnddc07...
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.

On my first boat, I thought I'd use epoxy on the stitch'n'glue part of the
project, and then switch to polyester resin for the glass lamination of
the bottom of the hull. Since I didn't know what I was doing anyway, I
bought a 1:1 resin/hardener type of epoxy (resin amber, hardener clear)
that comes in quart bottles in some hardware stores, which worked fine for
gluing and taping the joinery. But then, when I used the polyester resin
to glass the bottom, some kind of reaction occurred with the epoxy --even
after several days, the mating surface between the two resins had the
consistency of a runny gel that wouldn't harden. (To the best of my
recollection, the epoxy had already stood for several days in warm
daytime/cool nighttime No. Calif. tempertures of 80F+ to 50F+ and low
humidity of 40% prior to the application of the polyester resin, so it
should have been well cured, or at least set.)

(The question of whether to use polyester resin at all on a plywood boat
is another matter and has yet to be decided, since I understand that
polyester resin, even when fully cured, is not as impervious to moisture
as epoxy. On the otherhand, it doesn't seem to be as affected by UV rays
as epoxy, either, and since I don't intend to leave the boat in the water,
moisture may not be the bigger problem...)

Any knowledgeable insight or advice on the subject would be appreciated.

Thanks,
Carson

PS: The solution to the gel problem was to strip the hull to bare plywood
where possible & start all over using only epoxy--not an experience worth
repeating... Fortunately, the project was just a D4--another testamonial
to the wisdom of making your first boatbuilding project a small one...;}

YSTay wrote:
Hi, conventional wisdom has it that one cannot apply polyester resin on top
of (cured) epoxy. The amine in the epoxy does not allow for even a partial
cure of the polyester resin.

Polyester resin and gelcoat will work over FULLY cured and cleaned
epoxy. It will not work over partially cured epoxy. Regardless,
polyester resin is not the best product for laminating fiberglass to
wood. Epoxy is far superior.

"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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