Hi Barry

I would have to say that poor skills and bad work practice caused the
failure of the tabbing , not the amine blush of the epoxy.
The first BIG mistake the builder made was not following the designers
specs for construction to the letter.
The second stupid move was not reading the instructions for use of the
product he chose to substitute or being the least bit familiar with it.
I bet he made alot more mistakes too. scary

--
From the rocky shores of the Skykomish river
David Bosworth
http://www.premier1.net/~daveb/
Barry Palmer wrote in message
...
I have had hundreds of my customers using polyester resins on my Sevtec
surface
skimmer hulls without difficulty, and a few using epoxy, against my
advice,
with difficulty. In one case, amine blush of the epoxy caused the failure
of
tabbing that held some hull panels together and the result of using a
brake,
Yes, a brake on a surface skimmer, at about 35mph, caused the hull bottom
to
peel off, fortunately with no significant injuries, even though one person
of
three aboard went through the hole in the bottom and came up treading
water
behind the craft.

Epoxy is very critical in mix ratio, and that is why scales or
proportional
pumps are used, while polyester catalysis is easily done with a small
graduate
cylinder, and variations of mix ratio of 20%, which would certainly spell
disaster with epoxy, are of no concern with polyester.

Some structures do benefit from epoxy, but if the structure strength or
stiffness is governed by the glass, not the resin, epoxy may be a waste,
except
in long term exposure to warm climate salt water.



Subject: Polyester or Epoxy?
From: (Backyard Renegade)
Date: Thu, Jan 15, 2004 3:00 PM
Message-id:

(Ron Thornton) wrote in message
...
Bruce,

The "ordinary" people are the ones that can best justify epoxy because
the quantity they typically us is small compared to the production user.

To answer your question about why to use epoxy instead of poly is, that
it makes a better repair.

Regards, Ron

I don't recieve e-mail at this address because of spam. E-mail me
at crtsrATmsnDOTcom.

But that is really not even much of a factor anymore. To build a 12
foot skiff with flotation and proper materials, it is going to cost
you $250.00 on materials and hardware alone (assuming exterior plywood
hull), and just for ha ha's, say $25 for a set of plans. If you use
poly instead of epoxy, you might save $25 to $30 bucks max on the
whole build and more times than not, I have seen first time builders
end up using 2-3 times more poly than the plan would call for. The
learning curve for mixing poly is treacherous, (bring a good scale and
a calculator too) especially to the home builder that may be building
outdoors, or in a non conditioned barn, tent, etc.

Let me take a minute for anyone who is not clear about mixing the two
products.
With polyester, you must first calculate your catalyst ratio. So many
ounces of resin, to so many drops of catalyst. This mixture is not
only very delicate, but it changes depending on ambient temp,
humidity, how fast you want things to cure and the required
differences in the catalyst mixtures is very minute, and are based on
the starting formula plus the users best guess or experience of how to
alter that formula to suit the conditions at the time. Any very slight
miscalculation in the mix or even how many clouds will pass over
during the application can cause total havoc resulting in a slimy hot
slop all over your boat that is extremely difficult to remove (think
half hardened plastic mixed with cold roofing tar), that is to hard to
scrape, and to soft to sand, or a fast kick which catches you with
only half of your glass saturated, or just gobs up thicker and thicker
as you try to catch up and save something. In both cases the only
solution is a lot of elbow grease and lot's of wasted time and sand
paper, scrapers, and then a re-application.
With Epoxy, the cure rate is also dependant on the temp and humidity
of the work area, but not nearly as fast or as radical. Mixing is done
with calibrated pumps, something like one pump of resin to one pump of
hardener. If you want a faster cure, substitute a "fast" hardener, if
slower is your style or a bigger area to do in warmer weather, use a
slower hardener, no calculators, no precision scales, no guesswork at
all. If your pumps are working properly, and you don't get lazy
mixing, even mistakes will harden nicely to be ground or sanded off.

One extreme case (admittedly the most extreme I am aware of) was a
couple of years ago when I came in very late by e-mail on a build of
"Diablo", a 15 foot Bolger type skiff. The plan calls for 2 1/2
gallons of resin. This guy had a terrible summer of heat and cold,
never really got the mixtures down in his one build. He spent
literally dozens of hours scraping and sanding and just throwing out
resin that either kicked to fast, or not at all. He ended up using 11
gallons of poly on the build at a total cost of over $200 for resin
alone. Not to mention lost thickeners, thinners, brushes, sand paper,
scrapers, time, time, time, time, time... I will stop now, but he has
since built another boat, but this time he used epoxy, no problems.
Now I don't expect any first timer to build Diablo with 2 1/2 gallons
of resin, but certainly 3-3 1/2 should be the max.

One final comment. I do not know what the original poster should do, I
have no experience there, I don't do restores ;-) I also do realize
that poly has it's place in composite shops where big lay-up is done
or for molded parts, but somehow this thread seemed to get hijacked to
my area so I thought I would chime in here. So this has been my
advice, take if for what you paid.
Scotty from SmallBoats.com


BRBR

Barry Palmer, for A
HREF="http://members.aol.com/sevtec/sev/skmr.html"Sevtec/A