I guess what I should have said was, there should not have been any blush
to cause the failure in the first place, of course if it is left on the work
there will be little or no bond at all with what ever is applied on top.
This is not a failure of the product, but in the application.

--
From the rocky shores of the Skykomish river
David Bosworth
http://www.premier1.net/~daveb/
Barry Palmer wrote in message
...
I investigated the accident, and cut out a portion of the joint, and it
probably was amine blush, as the tabbing had contamination from sand and
silt
glued already on it at the bad joint, unlikely to have been in the joint
when
it was first assembled.

I now have builders put a doubler tab on this critical joint, that is 3
times
as wide, a small addition of weight for a lot of idiot proofing.

Subject: Polyester or Epoxy?
From: "David Bosworth"
Date: Sat, Jan 17, 2004 10:42 AM
Message-id:

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





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

BRBR

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

Well we all hear quite a bit about the evils and wonders of both
polyester and epoxy. But what about vinylester? Any one ever use
that? I'm curious because
I saw a vinylester/kevlar canoe prototype by Mad River Canoes that was
20 years old, light as a feather and showed hardly a scratch though it
had been dragged through gravel for years
SteveJ


Richard Lamb wrote in message ...
Ron Thornton wrote:

Hey Richard, just out of curiosity for the polyester crowd, how many
aircraft builders, hobby and commercial do you know of that ust
polyester?

regards, Ron

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

Not a single one anymore...

Even most of the kit manufacturers have changed over to epoxy.

OTOH, there is a growing use of vinyl ester resin.
It is catalized and works a lot like polyester, but with better
chemical resistance and much better physical properties.

Richard

"William R. Watt" wrote in message
...
"Meindert Sprang" ) writes:

I would think that counting drops is a very unreliable method. the drop
size
would be very dependant on the viscosity of the calalyst, right?

not so it's noticeable. one drop of catalyst for every 1/2 teaspoon of
resin.

Exactly! I have at least three sizes of teaspoons in my kitchen drawer.....
Which one is right? :-)

Meindert

"William R. Watt" wrote in message
...
no argument there. the question is when do you NEED the superior
qualities of epoxy?

Well, that's simple. I once tried to bond two pieces of mahogany together,
using glass mat and polyester. After curing, I could peel the stuff off,
something that I have never been able to do when using epoxy and cloth. So I
guess this is where you NEED epoxy.

Meindert

SteveJ wrote:

Well we all hear quite a bit about the evils and wonders of both
polyester and epoxy. But what about vinylester? Any one ever use
that? I'm curious because
I saw a vinylester/kevlar canoe prototype by Mad River Canoes that was
20 years old, light as a feather and showed hardly a scratch though it
had been dragged through gravel for years
SteveJ


well, in aircraft, Vinyl ester has become popular as a replacement
for polyester. One of the chief benefits is that vinyl ester is
not affected by the many solvents in auto gas. Polyester and many
epoxies will leach out in time and start leaking. That's considered
a bad thing, usually...

Richard

David Bosworth wrote:

I guess what I should have said was, there should not have been any blush
to cause the failure in the first place, of course if it is left on the work
there will be little or no bond at all with what ever is applied on top.
This is not a failure of the product, but in the application.

--

Im curious if using peel ply is a common technique in boat building?

This is a light layer of dacron or cheap polyester fabric placed over
the wet layup. When cured, the peel ply is "peeled" off leaving a clean
raw surface ready for the next lamination.

Takes the blush off too.


Richard

*you* can say epoxy is necessary all you want but *you* just don't know.
you might think you are qualified but you don't have any application data
to support your preference. what you have is material characteristics data
and anecdotal application tales. before this question can be settled
someone will have to do application testing. I doubt anyone would be
interested.

let me give you an example. the material characterisitcs of different
paints are known, but the performance of different paints under different
conditons are not. that is why the Post Office has to paint test mail boxes
with the different paints and leave them outside for years to see how they
perform. as an engineer with knowledge of the design and analysis of
experiments you'll appreciate its more complicated than just painting and
putting them outside.

its not just the materials characteristics that matter. it is the
combination of materials under varying conditions.

polyester lives.
long live polyester.

Ron Thornton ) writes:
No William, the question is are you qualified to make an informed
decision as to whether poly is good enough. I think not because I like
many others here, none of use having any interest in selling epoxy that
I know of, have worked with this stuff professionally for years at a
technical and engineering level and I doubt that any of us would be
willing to just look at all but the most obvious applications and know
whether epoxy was needed instead of polyester. You can say poly is good
enough all you want but the truth is that you don't really know. All we
are saying is that with todays price difference it is more affordable
than ever to go with epoxy and add an additional margin to a repair or
build.

please go back and re-read what I wrote. epxoy doubles the cost of a
small boat.

epoxy has been so overpromoted that people use it to sheath boats that
would be fine just painted.


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the materials characteristics of vinylester are between polyester and
epoxy: stength, flexibility, thermal stability, etc. I think Dave Gerr
gives the numbers in "Elements of Boat Strength".

SteveJ ) writes:
Well we all hear quite a bit about the evils and wonders of both
polyester and epoxy. But what about vinylester? Any one ever use
that? I'm curious because
I saw a vinylester/kevlar canoe prototype by Mad River Canoes that was
20 years old, light as a feather and showed hardly a scratch though it
had been dragged through gravel for years
SteveJ


Richard Lamb wrote in message ...
Ron Thornton wrote:

Hey Richard, just out of curiosity for the polyester crowd, how many
aircraft builders, hobby and commercial do you know of that ust
polyester?

regards, Ron

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

Not a single one anymore...

Even most of the kit manufacturers have changed over to epoxy.

OTOH, there is a growing use of vinyl ester resin.
It is catalized and works a lot like polyester, but with better
chemical resistance and much better physical properties.

Richard


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"Meindert Sprang" ) writes:

Exactly! I have at least three sizes of teaspoons in my kitchen drawer.....
Which one is right? :-)

are they metric or British teaspoons?
hint: turn over and look for country of manufacture.
if Japan, China, Tiwan, or Korea don't use.

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"Meindert Sprang" ) writes:
"William R. Watt" wrote in message
...
no argument there. the question is when do you NEED the superior
qualities of epoxy?

Well, that's simple. I once tried to bond two pieces of mahogany together,
using glass mat and polyester. After curing, I could peel the stuff off,
something that I have never been able to do when using epoxy and cloth. So I
guess this is where you NEED epoxy.

I don't think anyone would recommend polyester as an adhesive. However I
think you'll find plastic resin or polyurethane cheaper than epoxy and all
that is needed in a good many situtations, from laminating to
screwed-and-glued chine battens. I use the least cost adhesvie for the job
which means I have used epoxy in some situations.

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