Using epoxy & polyester resins on the same boat?

External Since: Jul 15, 2005 Posts: 2

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...;}

External Since: Jan 12, 2005 Posts: 61

"...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