Glacier Boats of Alaska - Builder's Forums
Great Alaskan and Boat Building => Boat Building Materials => Topic started by: fishon78 on November 04, 2019, 05:23:53 PM
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From what I have been reading I think this is the right kind of fiberglass mat. Can any of you share with me if this is the correct glass?
Hexcel 7781 - 38" - F3 9oz Biaxial woven glass mat suitable for EPOXY RESINS.
Thanks,
Fishon78
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From what I have been reading I think this is the right kind of fiberglass mat. Can any of you share with me if this is the correct glass?
Hexcel 7781 - 38" - F3 9oz Biaxial woven glass mat suitable for EPOXY RESINS.
Thanks,
Fishon78
There is exactly zero mat in the Great Alaskan fiberglass schedule. 'Mat' is omnidirectional glass fibers (shredded fibers in random direction) - It's used for core / fill on solid glass layups and adds no strength. THAT said, I do not believe that Hexcel 7781 has any true matting in it. That's good. BUT the description mentions that it's about half and half "fill yarn" and normal ("warp") yarn. "Fill yarn", I believe, is also known as "volumnized" or "texturized" yarn that is 'fluffed up' to absorb more resin. It is not as strong as regular ("warp") yarn and is an unknown quantity in terms of strength. I would choose to avoid 7781, although if it's already in your boat, it's probably OK - but I'd add a layer of 6-oz over the top to make up for lost strength in the "fill yarn".
Unless otherwise specified in the instructions, e.g. biax, all of the fiberglass called out for the Great Alaskan is standard "woven fiberglass" ... no mat, no volumnizing or texturing. It's also called e-glass, but don't trust the e-glass as the final answer ... read the description of the glass to make sure it's standard woven fiberglass that is compatible with epoxy resins.
Another type that I'd avoid is "satin" or "finishing" glass .... usually available in lighter weights. Fine for flat surfaces if the glass is provided on a roll (ALWAYS preferred since folding creates creases that don't go away and creases are also weaker), but 'finishing' glass doesn't want to follow a curve or hard turn worth a darn. I've used it. I won't use it again. :)
And because it's harder to fill and is allowed more defects per yard, I would also avoid "roving" fiberglass. It is woven fiberglass of the right type EXCEPT the yarn is larger in diameter and there are fewer strands of yarn per inch, which means the weave is more 'open'. You'll also find 'knot' type defects and sometimes missing little chunks of glass in it. It's intended to be a strength-providing fill layer of fiberglass. It's just as strong as regular woven fiberglass. If you use it, then scrape it smooth with a carbide scraper, add a fill coat of epoxy, and then add a layer of regular woven fiberglass to help minimize how much finishing and filling you have to do.
Finally - Avoid fiberglass that's listed to be "polyester" fiberglass unless you verify that the applied treatment works for both epoxy AND polyester. Some fiberglass is treated with chemistry that helps resins wet-out the glass, but some of those agents work for polyester and NOT with epoxy. Fortunately, this stuff is getting hard to find (except maybe on eBay) and the vast majority of companies now, if they use a wetting agent at all, use wetting agents that work for all types of resins. I still prefer to buy plain, untreated, standard woven fiberglass or e-glass (epoxy-glass) and be safe.
The attached image is a picture of standard 24-oz woven fiberglass. Lighter glass will have narrower yarn. In woven fiberglass, the yarn goes up and down, over and under, other yarn (see pic).
Hope this helps clarify some of the (confusing) fiberglass terms that you run into out there.
Brian