Fiberglass material help

i have a few questions about using fiberglass: what's the difference in weight? i see cloth coming in different weights like 16oz, 20 oz, 1.5 oz, and i'm not sure the difference and what weight i should use for what purpose. does the price go up as the weight go up, or vise versa? as a beginner what weight would work best for me? what's the difference between fiberglass chop strand mat and fiberglass cloth? aside from a resin, a hardener, and a gel-coat (is there any other type of releaser?) what else would i need chemical wise? what's a good place to find all these materials online for low cost? does anyone know a good simple tutorial for making a fiberglass shell from a form?

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Everfalling (author) 7 years ago
ok now that i've looked into it i've come across a whole other range of issues: the chemicals and what each are for. so far i've seen epoxy resins, polyester resins, hardeners, gel coats... and prolly a few things i haven't mentioned. can anyone tell me what i need to know about this stuff? i can't seem to find an all purpose instructional on how to use fiberglass, whether it's to mold make or to form a hard shell over a plug or whatever... i mostly see car repair videos that use bondo and other stuff... i'm really lost and beyond buying chop strand mat i have no idea what to buy... you wouldn't think this was that hard to figure out -_-
Epoxy and polyester resins are the main resins used for doing fibreglass. Epoxies are much stronger, don't require respirators for the vapours, and have a bunch of other desirable properties, but are more expensive. Polyesters smell awful, are the weakest resins used in fibreglassing, and are generally incompatible with other fabrics, like carbon and kevlar. The main difference in hardeners is time to cure, and for epoxies, UV absorbing agents. Each type of resin has it's own kinds of hardeners. I think a gel coat is some kind of finishing layer for polyester resins. I don't know much about polyester, but I know gel coats aren't used with epoxy. Fibreglass chopped strand is the cheapest fibreglass, it's a sorta just a mash of short fibreglass strands. Actual fibreglass fabric is woven. If you have any questions specific to your application, I'd be happy to try and help, but I'm by no means an expert on the topic.
Everfalling (author)  Ro]x[as7 years ago
thanks a ton that clears up a lot. is there any difference in weight between the two resins? in what situations would you recommend chop strand mat over cloth? and vise versa? also what if i want to separate the fiberglass from the mold? what releaser should i use? is there much difference between different releasers or can i just slather some Vaseline on there?
Uh as far as weight goes, I think most epoxies are probably more dense than polyester, but you have to remember that since the epoxy is stronger, you'd have to use more of the polyester to get the same strength.

Chop strand is usually used for things that don't require a lot of strength. The stuff is easier to get around complex curves than fabrics. Fabrics are normally used for structural parts. I haven't done much mold-making, but I hear that woven fabrics are usually not used because the weave pattern transfers through to the inside

To keeps the fibreglass from sticking to the mould, one usually uses PVA, but if using a metal plug, vaseline would probably work. PVA is cheap enough though, and works if using a plastic as the plug.

Oh, forgot to mention, another important difference between epoxy and polyesters is that polyester doesn't fully cure in the presence of atmosphere. That's the big reason for using gelcoats, I think. So if using polyester to make a mould, you'd need to line the inside of it with gelcoat, as well as the outside to make the thing cure properly.

There's plenty of mould-making guides on the internet. Like this one: http://www.fgci.com/howto/ht003fiberglass_mold.html
Everfalling (author)  Ro]x[as7 years ago
i'm trying to make a fiberglass shell over a form made from carved expanded spray foam. I'm told the foam will dissolve on contact with the resin. I've been told to prevent this i should use a hard shell foam coat like Ureshell but it's expensive. I'm wondering if it's possible to cover the form in plastic wrap and apply the fiberglass onto that. will the plastic wrap protect the form or will it dissolve too? I'm using epoxy resin.
It's over like expanded polyurethane? I've done that using epoxy, and it doesn't dissolve; I think it's just a problem with polyester resins. You can always try dabbing a bit of epoxy onto a scrap piece of foam and see. The nice thing about polyurethane is that once the epoxy has cured, you should be able to dissolve the foam using acetone or gasoline without harming the epoxy (usually, some polyurethanes are harder to dissolve than others; you might need like toluene or tetrahydrofuran).
I have asked questions about fiberglass here, but not many people know much. I will try to help though

-weight, I'm pretty sure that weight has to do with the weight per sq. yd of the cloth, heavier = stronger(depending on the weaves, bla bla bla.)

-cloth is the weaved variety, looks like fabric, its sometimes used for looks
chopped mat is just that, chopped. its a bunch of little strands of the glass formed into a mat, its ugly, heavy, sucks loads of resin and strong as hell if you use it correctly

-chem-wise, you dont need anything else, but there are thickeners, fillers, dyes/pigments, and so on for other purposes, also, gell coats arent needed, they give a gloss coat to the outside(if used with a mold, in which case you'll need a release agent like pva or pariffin)

-online prices will vary greatly, us composites seems ok, but you should do research and keep a cost spreadsheet if u have a budget, the glass itself is the cheapest part btw.

-tutorials, youtube has loads of tutorials for literally everything, even self breast exams(with very "detailed" video, if you catch my drift)

before you buy anything, do your homework, pricecheck, ask the hardware stores if they could special order some if itll give you a discount on shipping.