Thread: what is gel coat?

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just a quick question, what exactly is a gel coat or gel coat? do you put it on styrofoam to make it hard?

It's a polyester resin or epoxy that is usually tinted/colored. Gel coat is typically applied to fiberglass as a final smoothing coating over the hardened resin/fiber for a high quality finish. It could be used on its own I suppose, but honestly you would be better off just using the polyester resin, or fully fiberglassing whatever it is you want to strengthen. What type of application are you wanting to apply it to? Does it have a lot of detail?

You certainly can apply it to foam, but I'll need a little more information before I can make a recommendation.

oh okay and i didnt have anything in mind that i was gonna use it for i just thought maybe you put it on foam to harden it, thats all.

Been meaning to experiment with this kind of thing. There's also a product out there called Vanillacryl for "painting" a hard coat over foam but I don't see any reason why a gel coat wouldn't work. An epoxy coat (if you want something cheaper than West System get a 50% off coupon for Michaels (website or RetailMeNot) or Joann (have to sign up for mailing list) and get either Envirotex Lite or Castin' Craft epoxy (not resin). I get the feeling polyester resin would be more likely to melt/damage the foam (and your brain cells, it's STRONG). Either way, keep in mind that none of these products are UV stable at all. Epoxy must be painted or otherwise covered in something or it will quickly yellow and crumble.

Good recommendations. Although I have to insert a correction, in that polyester resins don't react with XPS (blue or pink high density) or EPS (white celled type) foams. Those types of foam are often used as core materials, and are sometimes the basis for large scale molds.


This is something I'd been looking at, a product called ArmorStone. The one thing that has put me off, is the very high price. Aquarium safe, paintable, and a of a gelcoat type that isn't solvent based. Which is ofc, more eco/human friendly. Additionally, it doesn't react to EPS foam.

http://www.polygem.com/zoo/armorstone.php

Originally Posted by Raven's Hollow Cemetary

Good recommendations. Although I have to insert a correction, in that polyester resins don't react with XPS (blue or pink high density) or EPS (white celled type) foams. Those types of foam are often used as core materials, and are sometimes the basis for large scale molds. [/url]

Good to know. I just know that the smell is enough to make me look for other products (though you can become touch-sensitized to epoxy quite easily, remember to always use gloves!). Polyester resin is much cheaper than epoxy though, you can get a nice big can of Bondo brand at Walmart for about $10-15. Do you do a fiberglass layer when you gel coat foam or is it optional? On a carved tombstone I figure there's pretty much no way you could fiberglass it and keep the detail.

It would be nice to use the less toxic option but costs tend to be high. I figure eventually these things will come down in price.

Originally Posted by Xane

Good to know. I just know that the smell is enough to make me look for other products (though you can become touch-sensitized to epoxy quite easily, remember to always use gloves!). Polyester resin is much cheaper than epoxy though, you can get a nice big can of Bondo brand at Walmart for about $10-15. Do you do a fiberglass layer when you gel coat foam or is it optional? On a carved tombstone I figure there's pretty much no way you could fiberglass it and keep the detail.

It would be nice to use the less toxic option but costs tend to be high. I figure eventually these things will come down in price.

Lol! I like the smell But yeah, it's not exactly healthy to be breathing the fumes of MEKP. The resin vapor isn't really harmful, except with extreme long term exposure. But the vapors from the hardener (Methyl Ethyl Ketone Peroxide) very much is. Not to mention, a pretty severe skin irritant, and long term exposure has been linked to liver failure & blindness among other problems. Not to scare you off, but always wear a respirator...or at the very minimum, work in a well ventilated area. My experience comes from molding/repairing body parts in a race fab shop, and I know the MSDS sheet by heart

With a polyester based gelcoat, yes you would want to use a layer of glass mat. Like I said earlier, I suppose that it could be used sans layer(s) of glass mat. I just wouldn't recommend it. The tinting of the gelcoat, at least the types intended for usage on fiberglass specifically, makes the resin weaker than it normally would be in it's pure form. They other types of hard coating products "stealing" the gelcoat name that we have both been looking at, I honestly couldn't say. I don't have any experience with them, so... -v0v-

Now, just using fiberglass typed polyester resin would certainly produce a very hard coating, and could be kept thin enough to allow for a good bit of detail. For thinning, you can only use 90/10 ratio of resin/styrene monomerm and do not vary the directed amount of hardener thinking you will get it to harden faster (it will only cause it to be of weaker structural integrity, and won't harden noticeably faster). That being said, it won't be able to keep fine detail without molding it. Very fine otoh, can be achieved with vacuum molding. Although that's not something many will have access to, even myself, being out of the industry nowadays. Like you surmised though, you will lose a bit of detail, even with just brushing on/spraying it without mat. Yes, there is a sprayable version too, marketed as a body filler which is pre-blended with primer. It works pretty well too, except the fact that no matter how awesome your spray booth is, you still can't get the smell out of the shop for days. It stinks horribly. :S That is only available to licensed shops/techs I'm sorry (happy?) to say.