"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. the drop squeezes out of a pinhole in a plastic container with a
bit of thumb pressure. works every time for me. I'd be more suspect of the
size of the pinhole but I've had no problems with it.

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I have mixed both epoxy and polyester for 35 years and have never had a
batch go bad. It ain't brain surgery. All you have to do is follow
exactly the manufactures directions. I have to agree with Meindert, if
you can't do that, you might want to think about whether you need to be
building a boat with two part resins! Only an amateur would
extrapolate to broad use the brushing on of catalyst over polyester
resin already applied to glass as described by Johns for one boat.
There is not a poly resin supplier in the word that would suggest such a
thing because there is no way to predict what the final properties would
be.

As to epoxy, I have mixed batches from 1 gal. down to 6 drops. Yes 6
drops (5:1 West) off of popsicle sticks for RC model aircraft building.
For larger batches I use any container of suitable size thats at hand
and mark off the ratio with a rule. Gee I'm glad I passed 7th grade
math.

Allan, the bottom line is that it is historically well established thru
industry testing, both lab and field, that epoxy is superior to
polyester in most ways except price. No amount of anecdotal evidence or
backyard observations as put forth by the polyester crowd will change
that.

Regards, Ron

PS. Meindert, I learned to measure epoxy in the lab at GE a long time
ago and was doing it on a balance scale until a couple of years ago I
was corrected by Kern of System Three and several other chemist here.
They all said that now the published ratios for the formulated resins
are for volume only as the weight ratio can be different. I never had
any trouble that I could detect but I do by volume ever since to assure
max mech properties.

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

Ron Thornton ) writes:

Allan, the bottom line is that it is historically well established thru
industry testing, both lab and field, that epoxy is superior to
polyester in most ways except price. No amount of anecdotal evidence or
backyard observations as put forth by the polyester crowd will change
that.

no argument there. the question is when do you NEED the superior
qualities of epoxy?

there are other questions about toxicity and so forth but the question
that most interests me is when epoxy is NEEDED. I've used it as an
adhesive in small quantities and to seal seams in some cases. If I used it
instead of polyester and polyurethane on the small boats I've made it
would double the price with no benefit I can imagine. everything has its
place. I don't consider epoxy to be the only product to use. No amount of
anecdotal evidence or backyard observations as put forward by the epoxy crowd
will change that.

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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.

Regards, Ron

PS for the hovercraft guy. Build one correctly out of epoxy and see how
long its service life is compared to the poly craft.

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

Longest is still in service after 18 Years, with no problems caused by use of
polyester resin glass skins over 4.5 lb "Clark Foam".

These surface skimmers have been built with epoxy, and appear to be little
different from the polyester, but possibly the elasticity of the panels is a
little greater, (possibly due to inaccurate mixing) bad news when a lot of the
structure is not governed by strength, but by stiffness.

PS for the hovercraft guy. Build one correctly out of epoxy and see how
long its service life is compared to the poly craft.

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

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

*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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Come on William, I didn't say epoxy is necessary. I said that without
an informed opinion (in part the application testing you speak of, which
I did at GE for 10 years) you had a better bet (guess) with epoxy. Your
right, I don't know. That's why at todays prices I chose to go with
epoxy and increase my odds.

You are the only one I'm hearing that says epoxy doubles the cost of a
small boat. In fact, so far the other builders seem to disagree. You
sure of that?

I agree that epoxy has been overpromoted especially in the area of
encapsulating wood but we're not talking about that here. Allans
question was what to use to repair a boat of poly glass construction.
For that amount of material I believe epoxy wins hands down.

Regards, Ron

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

Ron Thornton ) writes:
Come on William, I didn't say epoxy is necessary. I said that without
an informed opinion (in part the application testing you speak of, which
I did at GE for 10 years) you had a better bet (guess) with epoxy. Your
right, I don't know. That's why at todays prices I chose to go with
epoxy and increase my odds.

the original question was from a beginner who said the plan called for
polyester and was wondering if he should use epoxy.


You are the only one I'm hearing that says epoxy doubles the cost of a
small boat. In fact, so far the other builders seem to disagree. You
sure of that?

a quart of epoxy resin alone costs $32 without hardener or filler at
Candadian Tire. I'd probably only use a pint. however the most I've put
into one of my home made boats is $60. that was the expensive one. the
others were both under $25, including a tube of PL Preimuim at $3.99.

Lloyd Sumpter posted the same thing when he was costing out one of Gavin
Atkin's one sheet Mouse boats.

if you're a professional boatbuildier you have to include the cost of
labour, a boatbuilding yard, insuranace, tools, advertising, etc, etc,
which adds to the cost of the boat and lowers the proportional cost of the
adhesive. of course if all the customers want epxoy because they've been
conditioned by advertisign to expect epxoy, then one has to build with
epoxy. you're also likely to use epoxy to avoid any risk of lawsuits if
the customer runs his boat onto the rocks. since the customer pays for the
epxoy then why not use it? you get that mentality a lot with canoes.
ignorant people influenced by advertising want kevlar and expoy because
they think they can run survive bigger rapids, sigh.


I agree that epoxy has been overpromoted especially in the area of
encapsulating wood but we're not talking about that here. Allans
question was what to use to repair a boat of poly glass construction.
For that amount of material I believe epoxy wins hands down.

I've borrowed books and videos on boat repair from the public library
which adivse using polyester to repair polyester boats. I've used it
myself on the few small repairs I've done. If people are more comfortable
with epoxy I guess that's what they will use, if only for peace of mind. I
can't help wondering how much epoxy promotion has to do with peace
of mind. First you raise people's anxiety level, then you lower it again.
Advertising is beautiful.


Regards, Ron

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



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"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

"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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