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Gelcoat ???

R/C Submarine modelers

Gelcoat ???

Postby modelnut » Mon Sep 05, 2011 4:51 pm

What is it? How do you apply it? And what kind should I get?

A friend says that I need it to give my scratchbuilt hull a surface that I can detail. Says that the fiberglass surface will be to crumbly to etch details such as hatches and plates into. I can see his point a bit. When I sanded the fiberglass smooth I saw a bit of fuzz from the glass cloth. A few coats of grey primer and light sanding took care of that. But I can foresee problems if I start scratching the surface.

So what is the deal with gelcoat. I have searched the forums and don't see much info for me, the beginner. Could someone set me straight? Give me a few pointers?

- Leelan
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Re: Gelcoat ???

Postby Thor » Mon Sep 05, 2011 6:24 pm

What type of process are you using and what type of resin system are you using....polyester or epoxy? Molded up hull from a female mold, or is this a lost foam method?

Matt
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Re: Gelcoat ???

Postby salmon » Mon Sep 05, 2011 6:36 pm

Thor,
I do not know if this will help here is his build....viewtopic.php?f=35&t=10582&start=15

Regards,
Tom
If you can cut, drill, saw, hit things and swear a lot, you're well on the way to building a working model sub.
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Re: Gelcoat ???

Postby modelnut » Mon Sep 05, 2011 7:08 pm

Thor wrote:What type of process are you using and what type of resin system are you using....polyester or epoxy? Molded up hull from a female mold, or is this a lost foam method?

Matt


My fiberglass and cloth came from Lowe's. Then I applied two coats of Evercoat Metal Glaze. I sanded all that pretty near smooth and covered it all with Krylon Primer Grey to check for flaws. Taking everything all together the hull's thickness is about 1/8th inch.

This is laid over a hollow paper model hull reinforced with cardboard bulkheads and duck tape. I was going to do a lost foam build-up but this paper model had the perfect shape for my boat and I thought, "Why the #377 not?" It saved a lot of work even without having to lose the foam. One scratchbuilder used duck tape so that his fiberglass would not stick to his buck. It worked for him so I am trying it. The hull will have to be nearly finished before I found out if it worked in my case.

I almost asked this same question on my build thread but received no responses. So I thought I would see what I could get here.

- Leelan
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Re: Gelcoat ???

Postby andyn » Tue Sep 06, 2011 6:19 am

Gel coat is a thick resin that is used in mould making as a top layer. The Gel goes in first, then matting on top.

Don't use Gel Coat on the outside of a built up hull, it requires an anaerobic environment to go off. If you paint it on the outside of the hull it will never cure.
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Re: Gelcoat ???

Postby Thor » Tue Sep 06, 2011 10:02 am

Gel coat can be applied as a top coat to any polyester resin layup. It can even be sprayed. However, you must spray PVA on it for it to cure. The PVA washes off very easily with soap and water leaving behind a very nice shiny and hard surface that will accept detailing very nicely. In my humble opinion, epoxy is the way to go, but that is a personal preference.

Matt
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Re: Gelcoat ???

Postby modelnut » Tue Sep 06, 2011 5:04 pm

Thanks, guys!

Since I will be painting the hull anyway it won't matter what color gelcoat I get, right? Something light that will show pencil or Sharpie marks that will later be engraved. I will also ask about the PVA spray at the marine shop when I go.

My NAUTILUS is currently in a friend's hands. He has all sorts of nifty tools like lathes and jigsaws and what-not. He has volunteered to make a stand or cradle that will hold the hull level and secure for detailing. So I will hold off getting the gelcoat etc until he gives me the word that the cradle is near completion.

In the meantime I will be scratchbuilding the wheelhouse. Maybe a some other things too. But I will try not to get too carried away. Just my luck there will be some crucial measurement that I will be completely sure of that will turn out to be completely wrong. So I will try not to get too carried away until I have the hull back home. :roll:

- Leelan
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Re: Gelcoat ???

Postby Thor » Tue Sep 06, 2011 5:23 pm

PVA is a liquid that must be sprayed with an airbrush or automotive detail gun(my preference). Spray on 3 very light coats to seal the gel coat.

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Re: Gelcoat ???

Postby modelnut » Tue Sep 06, 2011 5:40 pm

Thanks, Matt,

Do I need to sand the primer off before I apply the gelcoat?

- Leelan
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Re: Gelcoat ???

Postby Thor » Tue Sep 06, 2011 6:48 pm

Leelan. If you insist on applying gel coat, yes. You need a very nice smooth and clean surface. No contamination. If not you will get all sorts of bubble and voids and other nasties that you will have to deal with....

Matt
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Re: Gelcoat ???

Postby modelnut » Tue Sep 06, 2011 7:09 pm

"Insist" ???

I didn't think there was an option.

I need a smooth surface that I can scratch details into. Is there something else I can do? Something easier? Better?

My friend says that gelcoat is a "self-leveling resin coating" that would be perfect for the job. Trouble is that he has never done it. He has an extensive background in modeling and machining and tool construction. But I imagine that there may be gaps in his knowledge.

This is my fourth attempt at a scratchbuilt hull. I would like to avoid any more avoidable and/or costly errors. You guys are about the only help or advice I can find.

- Leelan
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Re: Gelcoat ???

Postby ManOwaR » Wed Sep 07, 2011 12:14 am

Leelan,
Matt's very right about the surface preparation, you want that coat to stick. Instead of a traditional gel coat on top of a one off hull like you're doing, I personally would go the route of using an automotive high-build epoxy primer like XTREME DTM High Build 5425. It adheres better than a polyester gel coat would, is very easy to sand and will accept scribing tools excellently. The downside to this stuff, like any other good quality automotive product is that its expensive and should be applied using an appropriate air gun. You can also brush it on, block sand the brush marks smooth and repeat a few times to get a good thick coat and that should work well too if you don't have air tools.

Another good product is DURATEC VINYL ESTER PRIMER. Much cheaper than epoxy. It adheres to fiberglass better than polyester but still not as good as epoxy. It's still pretty hard but scribes VERY well and gives you clean lines. It needs more (lots! lol) elbow grease however to knock down orange peel or brush marks than the epoxy.

When block sanding any of these surfaces smooth, it is a good idea to use a cheap black spray paint over top of you're surface before you begin sanding . As you sand, the black paint will reveal pits, pinholes and low spots that you want to concentrate on.

Hope this helps,
Joel
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Re: Gelcoat ???

Postby Thor » Wed Sep 07, 2011 12:44 am

Gel coat is anything but self leveling! Don't use it if you don't have to, and you do not have to! Follow Joel's recommendations and you will have much better results.

Matt
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Re: Gelcoat ???

Postby modelnut » Wed Sep 07, 2011 6:50 am

Thank you!

I will look for that stuff instead. I don't have any auto spray equipment so I will try brushing. Will keep you posted.

- Leelan
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Re: Gelcoat ???

Postby modelnut » Wed Sep 07, 2011 10:49 am

Damn. No auto parts store in my area has ever heard of XTREME DTM High Build 5425. Neither has their parent companies. I can get it on eBay for $65 though.

Funny. No one here ever heard of Evercoat Metal Glaze either. I know I live out in the boonies but this is ridiculous! We have Autozone, Pep Boys, Napa, Precision etc. But none of their websites have ever heard of any of this stuff. :evil:

- Leelan
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