polyester - epoxy bonding

[Walt]

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

[Walt]

>
> hypothecated on driving over rocks, you would do better to study
> the charts.

Well, I did GET the hole by "driving" over a big rock land sailing... I was
hoping the rock might take the damage next time.

[Terry Spragg]

When I patched a 3" thru hull hole on my 3/8" thick HR28 hull,
all polyester glass, I used a 'feathered' polyglass patch and
could not see it after it was done. I cannot imagine the bond
failing, I tried to dig at it with an awl, etc. There is no way
I would not use epoxy to repair polyester, because from then on
you would need to cover it with epoxy. It would complicate even
bottom painting. Grind out all the epoxy, rough sand, clean with
acetone and restore it to like new with like material.

Don't think about it too much. Do it like the pros do. Feather
the edges inside and out, and learn how to mix and glop
polyglass.

If you are worried to the point of doing engineering studies
hypothecated on driving over rocks, you would do better to study
the charts.

Opinions, opinions, ever'body gots opinions.

Terry K

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

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[William R. Watt]

Walt ) writes:
>>
>> hypothecated on driving over rocks, you would do better to study
>> the charts.
>
> Well, I did GET the hole by "driving" over a big rock land sailing... I was
> hoping the rock might take the damage next time.
>

perhaps if you glass the rock the boat will slide over.

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[Ron Thornton]

Best bond is with epoxy, rock or hull.

Ron

[William R. Watt]

Ron Thornton ) writes:
> Best bond is with epoxy, rock or hull.

not if "best" is "the lowest cost bond which satisfies the requirement".

to prove the hypotheisis that epoxy is the best resin to glass a rock so a
boat will glide over it you have to perfrom a controlled experiment with
sufficient replications to be statistically significant. my money would be
the polyester as the lowest cost bond which would meet the requirement.



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[William R. Watt]

Ron Thornton ) writes:
> William,
>
> What part of "best bond" didn't you understand or are you just trying to
> start an argument.

its an old argument. "best" is not "best" when it costs more than needed
to do the job. there are lots of ways of saying it, like using a cannon
to kill a fly.

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[Ron Thornton]

William,

There is no argument in the context of this thread. Walt already has
done the repair with epoxy so cost is not a consideration. He seemed to
be asking if polyester would be better. I say no way.

Epoxy is best because its bonding abilities are well documented compared
to polyester. To prove that polyester is good enough for coating a rock
(or any one time repair) requires a guess or some testing. Neither
approach is worth the risk of using an inferior materal because of the
cost difference between E and P for the normal repair jobs we discuss
here.

Ron

[Backyard Renegade]

(Ron Thornton) wrote in message >...
> William,
>
> There is no argument in the context of this thread. Walt already has
> done the repair with epoxy so cost is not a consideration. He seemed to
> be asking if polyester would be better. I say no way.
>
> Epoxy is best because its bonding abilities are well documented compared
> to polyester. To prove that polyester is good enough for coating a rock
> (or any one time repair) requires a guess or some testing. Neither
> approach is worth the risk of using an inferior materal because of the
> cost difference between E and P for the normal repair jobs we discuss
> here.
>
> Ron

Ron,... Hey, I wuz just having a little fun with William when I
mentioned the rock, and btw, I have done the tests and you might be
surprised at the result... a lot has to do with the color of the
rock!...
Sorry, I did not mean to start a fuss.
Scotty, going back to my rocks...

[Mark]

>> "best" is not "best" when it costs more than needed
> to do the job

Yea, that was my protocol in early years of boat ownership. Now, if
the materials cost isn't significant compared to the labor and hassle
effort, I always buy the "best" stuff at whatever I'm trying to do,
which would be bond strength if fixing hull holes. Also go for
user-friendly; epoxy doesn't give off fumes when polimerizing. Now,
if i needed a hundred gallons of resin for a job, I'd look close at
whether polyester resin would suffice.

[Ron Thornton]

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

Ron

[William R. Watt]

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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[Ron Thornton]

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

[Paul Oman]

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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Frog Pond Hollow - 48 Wildwood Dr - Pittsfield NH 03263
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http://www.epoxyproducts.com
Boating site: http://www.epoxyproducts.com/marine.html
================================================== ======

[Ron Thornton]

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

[just_passing@]

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.

[Ron Thornton]

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

[Ron Thornton]

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.

[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.

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

[Ron Thornton]

Well there you go. Another unsolicited testimonial.

Epoxy rules.

Ron