On Sun, 09 Nov 2014 10:58:42 -0500, Ed Huntress
wrote:

On Sun, 09 Nov 2014 13:46:11 +0700, John B. Slocomb
wrote:



The WEST Systems people have done tests of epoxy and common chopped
mate, see:
http://www.westsystem.com/ss/chopped-strand-mat-epoxy/
and while they don't suggest it as a first choice they do say that it
is usable.

OK, I had a few minutes and read that link. That's the one I thought
it was; WEST published it over a decade ago.

Ed, I've got instructions that date back a hundred years or more and
are still correct.

The stitched mat he mentions is the stuff made for use with epoxy.
That's not the mat we buy that's made for use with polyester. The
stitched mat has no binder.

No Ed, he mentions that there is stitched mat made for use with epoxy
but the article was very obviously written to discuss the use of epoxy
with regular old chopped mat sold for use with polyester.

In fact WEST says, in part, "Testing in warm/moist conditions:
To see if our concerns were justified, we compared samples of generic
chopped strand mat (wet out with WEST SYSTEM 105 Resin and 206
Hardener) against samples made with our Episize fiberglass fabrics
(wet out with 105/206)"... "Our test included three specimens of
chopped strand mat, two different sources of 1.5 oz and one 3 oz. One
of the samples was made with generic mat found on the fiberglass rack
in our shop, and the other two were purchased from Composite
Structures Technology in Tehachapi, California. (661-822-4162)"

The author wrote sbout his experiments and said regular mat "should
work fine" on gently curving projects.

Maybe. If the curve is too much, you can have one hell of a mess. The
fibers start to pull away as you work it; some stick to whatever
you're bonding to, and the rest tend to tear loose as you keep working
it, trying to get around the bend or curve.


Not to be sarcastic but I believe that you are getting into the a
totally different area than whether it is possible to use common
chopped mat with epoxy or not. You tried and failed; I tried and
succeeded.

Unlike polyester, you don't get that sharp initial gel stage with
epoxy. In tends to just keep getting thicker. With polyester, if the
project isn't too large, you can mix it a little hot and just keep
poking it with the end of a brush, or rolling it, until it takes the
shape you want. It will still adhere in the early stages of gelling
(so will epoxy). That will take only ten to fifteen minutes, at most,
with a moderately hot polyester mix -- one that isn't too hot to
produce good finished properties.

Getting cloth around a corner, with no mat, can also be difficult with
epoxy. In general, it's much harder to work with, if there is any
complexity to the shapes you're trying to cover, than polyester. If
the surfaces are flat, or nearly so, it's no problem.

Again, you seem to be sliding off in a different direction. As I said
before, you tried and failed. This is not evidence that it doesn't
work.

After all I succeeded :-)

--
Cheers,

John B.