There is also stitched mat, manufactured specifically for use with epoxy. It
isn't glued together with styrene -- it is stitched instead, so no problems
with "sizing" not dissolving. And since it wets-out clear, the same as
cloth, it's much easier to determine when you are saturated and when you're
not. But it is also entirely possible to use epoxy with plain chopped-strand
mat in many situations. I used it when rebuilding the cabin on my former
CT-41, laying down one layer of CSM between the cloth and plywood to help
prevent delamination (belt and suspenders approach). Regular CSM doesn't
soften much with epoxy, but on flat and gently-curving surfaces that isn't a
problem at all. Still, if stitched mat is available, it is certainly the
better choice.

http://www.westsystem.com/ewmag/21/chopped.html
http://www.shopmaninc.com/mat.html

--
Karin Conover-Lewis
Fair and Balanced since 1959
klc dot lewis at centurytel dot net


"Glenn Ashmore" wrote in message
news:g5Jwc.24171$My6.1770@fed1read05...
That is one exception to the rule. 1708 is 17 oz bidirectional knitted
to 8 oz mat. Strong and builds up bulk quickly so it is good for
repairs and tabbing. It can be used with either polyester or epoxy.
The sizing in the mat does not dissolve in epoxy so it will not turn
clear the way plain glass does but the un-sized bi-directional top layer
bonds to the substrate well. A side advantage is that it is easier to
work. Bi-directional has a bad habit of stretching out of shape when
handling after it is wet out. The mat helps it hold together better.

Dan wrote:
You aren't talking about using this with epoxy right?


I'd go for some biax with the mat already stitched to it. A little more
pricey but much stronger and should not be as resin thirsty. You'll get
more bang for the buck.

--
Glenn Ashmore

I'm building a 45' cutter in strip/composite. Watch my progress (or lack
there of) at: http://www.rutuonline.com
Shameless Commercial Division: http://www.spade-anchor-us.com

Mat is used in polyester laminations to improve the bond between
layers of woven glass. Polyester has poor bonding qualities and that
is why mat is used.Woven on woven in a polyester matrix has poor peel
strength.
Epoxy has greatly superior bonding properties and mat would be a waste
if used for that reason. Mat can weaken an epoxy laminate properties
by increasing the distance between the layers of woven.
(woven includes directional).
The only reason to use mat is to add bulk - thickness - stiffness or
resistance to impact.
For that purpose, mat shoud be used towards the middle of the laminate
stack.
It does not add strength.
This happens in small boats in which the skins are too thin for
adequate stiffnes or resistance to puncture.

Jacques from bateau.com

Perhaps. In my own tests, which I performed prior to glassing my cabin, the
laminations which used csm between the glass cloth and the plywood had
better (though not really significant) peel resistance. It has held up
extremely well over the years (approaching 10), so I would do it again.

--
Karin Conover-Lewis
Fair and Balanced since 1959
klc dot lewis at centurytel dot net


"Jacques" wrote in message
om...
Mat is used in polyester laminations to improve the bond between
layers of woven glass. Polyester has poor bonding qualities and that
is why mat is used.Woven on woven in a polyester matrix has poor peel
strength.
Epoxy has greatly superior bonding properties and mat would be a waste
if used for that reason. Mat can weaken an epoxy laminate properties
by increasing the distance between the layers of woven.
(woven includes directional).
The only reason to use mat is to add bulk - thickness - stiffness or
resistance to impact.
For that purpose, mat shoud be used towards the middle of the laminate
stack.
It does not add strength.
This happens in small boats in which the skins are too thin for
adequate stiffnes or resistance to puncture.

Jacques from bateau.com