Even on the hundred gallon jobs epoxy is used for high quality work. It
ain't cheap but it is the best.

Ron

Ron Thornton ) writes:
Even on the hundred gallon jobs epoxy is used for high quality work. It
ain't cheap but it is the best.

it is the strongest resin with the strongest adhesive bond (to most woods).
whether it is the best in any given situation is debatable.
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Dan,

Back in the dark ages (almost 40 years ago) when epoxy was $40 an oz.
(or so it seemed) one of the first rules I learned was "never put
polyester on epoxy". Because of the cost back then almost no one used
epoxy for boat building or repair. This caused us to use poly in
adhesive applications that it was not very good at. I can vaguely
remember roughing up a surface for poly with something like a 26 grit
disk and then going back with a box knife and scoring the surface. You
never laid glass on a surface that had been painted. No matter how much
you sanded the poly just wouldn't stick and when I glassed new plywood
the first coat was thinned with styrene 30 to 50% to ensure a decent
bond. And of course you couldn't glass over planks because the tensile
strength of poly was too low, the glass would break at the seams when
the wood swelled. On top of all the above, it took a lot more poly to
do the job.

Life is so much easier since epoxy got relatively cheap.

Ron

Walt wrote:

I have a polyester/ glass laminated part (gelcoat on one side) and I
need to repair a hole in it. In the past, Ive sanded the
glass/polyester, cleaned it up with acetone and then used west epoxy and
"boat tape" glass. The polyester part is about 4 years old.

This works reasonably well but the bond doesnt seem as good as the
original polyster glass to glass laminations or if I were bonding epoxy
to epoxy.

Any suggestions on a really strong way to fix holes in polyester
laminated structures or improvements on what Im already doing would be
appreciated.

Regards,

wh

Hello:

In my probably distorted brain the 'view' is that polyester bonds well to
itself and only so-so to other materials (lots of first and second hand
experience of polyester resin to wood failures after about 8 to 10 years),
but epoxy bonds well to lots of things, including polyester.

paul
www.epoxyproducts.com/marine.html


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================================================== =====
PAUL OMAN ----- Progressive Epoxy Polymers, Inc.
Frog Pond Hollow - 48 Wildwood Dr - Pittsfield NH 03263
603-435-7199 FAX 603-435-7182 VISA/MC/Discover
http://www.epoxyproducts.com
Boating site: http://www.epoxyproducts.com/marine.html
================================================== ======

I believe epoxy bonds to cured poly better than poly to cured poly, but
it's been so long I'm not sure. Any chemists out there?

Ron

On Wed, 16 Jul 2003 22:53:28 -0400 (EDT), (Ron
Thornton) wrote:

I believe epoxy bonds to cured poly better than poly to cured poly, but
it's been so long I'm not sure. Any chemists out there?

Ron

Once its cured its all the same - its just another surface.
But epoxy would have the better flow, as a wetting agent, ionic.

So better able to get into all the scratches etc -so its about its
mechanical ability to flood the surface area completely.
While poly is a bit lumpy as in viscosity

But you can test it by sticking a piece of paper in both see how they
climb. Or a measured drop on paper and see which makes the biggest
circle, for spread, That kind of testing will give comparisons. plus
others.
I have stuck stuff with poly, its okay - but its not considered an
adhesive as epoxy.

Thanks Rubbish,

I guess that's why we went to such extreme to make the surface rough for
poly when it was the only reasonably priced resin. Trying to make a
silk purse out of a sows ear I suppose.

Ron

Al,

I don't think you will know if it is a success for some time. What you
have done is made an educated guess that it will bond good enough for
something on display. Nothing wrong with that and it sound like you
would not make the same decision if the use was marine

Ron.

I don't think you will know if it is a success for some time. What you
have done is made an educated guess that it will bond good enough for
something on display.

the oars were left out in a rainstorm and were bounced around on a trailer
(the roads are awful around here) before I gave them back to the boss who
pronounced them perfect and upped what he was paying per oar by 50p. When
these things are painted and nailed to a pub wall the bond is going to be
more than enough.

Nothing wrong with that and it sound like you
would not make the same decision if the use was marine

If I had some very cheap oars that I didn't mind bashing around I would, but
the oars I repaired could not be used for their designed purpose simply
because the filler is soft (designed for easy sanding) and it would be
ground off far too easily. No, I wouldn't trust a polyester-over-epoxy bond
in anything that had to take any kind of abuse. Something that is static
with a reasonable key? yes.

After seeing the mess that my dad's boat is becoming I have strong
reservations about using polyester in a marine environment period. It looks
as if water has been able to permeate the polyester/glass covered wood, but
it has been held there whereas in the surrounding varnish only wood, the
water seems to have been able to escape appearing to do less damage. I need
to tear into much of the keel and hog to shift rot and the wood I remove is
going to be replaced by epoxy, but I think that boat is well and truly on
it's way out after only perhaps 20 years, mostly through poor maintenance
(if I'd known 5 years ago what I know now it'd be a much different story...
but I'd also have been 13). Polyester did the job when there was nothing
better, and in the lamination of large amount of fibreglass may still be the
material of choice, but better materials do exist for this application now,
and at reasonable prices.

Al

Well there you go. Another unsolicited testimonial.

Epoxy rules.

Ron