Polyester glass different from Epoxy glass - RC Groups
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Jan 01, 2010, 02:03 AM
Slope Stud

Polyester glass different from Epoxy glass

I got some free glass and I was told there is a difference between glass made for polyester resin and glass made for epoxy resins...

I didn't know that.

How do you tell the difference???

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Jan 01, 2010, 02:51 AM
Registered User
Polyester glass has a chemical in it which makes the resin wet the mat out better. I've only struck this with Chopped Strand mat. In my experience any woven cloth should be good with either Poly or Epxoy.
Jan 01, 2010, 08:06 AM
Will fly for food
Actually chopped strand mat is made for polyester resin. The binder used to hold it together will solubilize/wet out with ester resins (polyester or vinyl ester) but not with epoxy. So you need a special mat for epoxy.

But cloths are typically all the same.

BTW the binder used in chopped strand mat is typically starch.
Jan 01, 2010, 08:15 AM
Registered User
The SKY MAN's Avatar
are we saying chopped strand should not be used with epoxy?
Jan 01, 2010, 09:08 AM
Registered User
stevext's Avatar
I was always taught to keep chopped strand mat (csm) for use with polyester resins and wovens with epoxy due to the binder in it as stated in the other post.


Jan 01, 2010, 11:31 AM
Composites Kid
Alex.Schweig's Avatar
Some mats do work with epoxy and polyester as well as vinylester.

Most chopped strand mats, however, work only with polyester and will not make a good chemical bond with epoxy.

Cloths always have a "finish" or "sizing". The purpose of the finish is to promote the bond between the fibers and the matrix, thus stabilizing the composite.

"Volan", the most common finish in fiberglass cloth, is compatible with epoxy, as well as polyester and vinylester. "Silane" finish is usually found in S-2 glass cloth, and compatible with epoxy. The last finish is F-16 finish.
Jan 01, 2010, 11:37 AM
Slope Stud
That's great..

I got 2 huge rolls of fiberglass and now it looks like I will be able to use them..

Stuff I got for FREE today....

Jan 01, 2010, 11:52 AM
Composites Kid
Alex.Schweig's Avatar
Hi Oran, have you any idea what the weaves are?

The second looks like a stitched double bias.

If they are 40oz cloths, then they are bound to be stitched with at least two layers

Jan 03, 2010, 02:52 PM
Registered User
stevext's Avatar
I'll guess at the bottom cloth being a biaxial too but the top one reminds me of a uni-directional roll?
Jan 03, 2010, 04:10 PM
ak79's Avatar
Be careful, if you need to go around some complex shapes, the epoxy won't disolve the binder in glass that's supposed to be used with poly. So it ends up being a bear to work with. I've used that stuff with epoxy plenty of times to build mold thickness, but best suited for flat projects.

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