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morganbill 12-22-2006 12:34 AM

Epoxy Resin and Mat Fiberglass
I have a small fiberglass repair to make and while reading Dan Casey's book discovered that he discourages the use of epoxy resin (West System) and mat fiberglass. He recommends using fiberglass cloth (10 oz.) Looking for a confirmation as I inteded to use a layer of mat, roving and mat with West System 105.

sailaway21 12-22-2006 01:13 AM

Casey advocates that from a strength standpoint. It has nothing to do with the epoxy resin being used. Mat has littlr strength but is easily shaped (faired). Rove on rove is weak without mat in between. Cloth with mat gives you strength, flexibility in application, and shaping ability. Much depends on the size of repair, with cloth being the easiest and strongest to work with on small areas. West system has free literature that is quite good on the subject; between them and Casey you'll not go too far wrong.

Tartan34C 12-22-2006 06:07 AM

Epoxy and mat
The binder for some types of mat may not be soluble in epoxy so it’s hard to wet mat out if you use epoxy. If you want to use mat make sure you buy suitable mat and that may be the only problem with using mat and epoxy. In the past you couldn’t buy mat that had such a binder so it got a bad reputation with epoxy but I have been told that this is no longer true. The only time I tried mat with epoxy I found this wet out problem to be true but that was years ago and I have only used polyester with mat since then. So I don’t know first hand if suitable mat is available.

Mat is used to add bulk or act as a tie between layers of something else. Mat is easy to sand and makes a great finish layer. Roving and cloth are stronger but don’t bond well to themselves or each other so mat is also great between layers. I use polyester resin for repair work on boats and it's fine. Epoxy has higher peal strength but you don’t need that with a repair so way add the extra expense and complication by using epoxy?
Good luck with the repair,
Robert Gainer

hellosailor 12-22-2006 10:10 AM

"West system has free literature that is quite good on the subject; "
And they're great about answering questions on the phone. You pay for the call, they'll tell you anything you want to know about FRP including specifics for your job. Can't beat that.

feetup 12-22-2006 10:20 AM

epoxy 'n' mat
The binder referred to is sprayed on to the mat in manufacture to hold the loose strands together. It is a styrene and is disolved by the polyester just like a styrofoam cup, allowing the fibers to splay and move independently. In the same way that you can lay-up over styrofoam using epoxy the mat will not achieve it's wet dishcloth state if the binder is not desolved.
If you are concerned about the added strength, flexability and adhesive qualities of epoxy you might think of using a vinylester resin which falls somwhere in between epoxy and polyester in most catagories and I believe has no issue with the soluability of the styrene binder.

Cheers, Feetup

sailingdog 12-22-2006 03:51 PM

Actually, the binder used in a lot of the fiberglass mat products is not compatible with epoxy. In many cases, it is specifically formulated to work with polyester/vinylester resins. Fiberglass cloth is much stronger and the longer fibers in it tend to lead to a much stronger repair.

C27Shockwave 12-22-2006 06:16 PM

Check out the System3 website. They have a free book you can download. And free advice via e-mail. Their products are excellent. If you need strength, use fiberglass cloth. It lays out nice and takes the epoxy well. It may be a little more expensive but, you'll have no regrets. and are a couple of boat building sites that have some valuable info too.


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