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bristol299bob 08-03-2012 05:13 PM

Spraying gelcoat
The recent <a href="">Why paint instead of gelcoat?</a> thread was very interesting, and timely too. This winter I plan to refinish the deck, cabin top and cockpit of my 35 year old Bristol 29.9. The original gelcoat is scratched in a few spots and seems to have “pin holes” in other areas. My original plan was to paint the deck, but after reading the thread I realize that spraying gelcoat is actually an option for me.

I don't want to rehash the pros and cons of gel vs paint in this thread. I've decided that I will be spraying gelcoat. I'm a rookie, but I will be doing it myself. I've got a few months to practice.

Most of what I have read about spraying gelcoat involves doing the topsides. In my case I will be doing the deck, the smooth portions between the anti skid. So I dont have any big areas to cover. Of course the small sections are spread out of the whole boat, and some of them extend the length of the boat.

so a few questions:

<li> Practice. Can I practice on wood scraps (plywood etc) or is it too porous to give a decent finish? If not what can I practice on? (I dont have hunks of fiberglass ... )

<li> The preval sprayer a reasonable choice? Its seems the easiest for me at this point and I think it would be fine for the relatively small sections that I am doing. But I could go with an HVLP sprayer and borrowed compressor if that is the way to go in this case.

<li> With paint, roll and tip, you need to keep a wet edge, but I am wondering if that is the case with gelcoat. Can I do a section, say the side decks from stern up to the shrouds. Then the shrouds forward the next day? Or do I need to shoot it all in one go? (this may determine if I can use the preval sprayer or not … )

<li> Also plan to do the antiskid. Kiwi Grip was the plan, but now Im wondering if stippled gelcoat would be the natural choice at this point. thoughts on that?

<li> Materials:
<li>duratec additive: yes?
<li>thinning: use styrene or “patch booster”?
<li>surfacing wax: for all coats or just the last?
<li>coats: how many?

thanks everyone!

MastUndSchotbruch 08-03-2012 08:22 PM

Re: Spraying gelcoat
If you want to use a preval sprayer, you will find this link interesting: Spray Gelcoat in detail | Preval

PorFin 08-03-2012 08:35 PM

Re: Spraying gelcoat

Before you commit to applying new gelcoat, please take the time to read MaineSail's excellent how-to narrative on restoring an aged/weathered gelcoat surface. You may find that your old gelcoat will respond and come back to a good as new luster.

Start with a small area -- if it can be restored by only sanding/compounding and polishing, then you're gonna save yourself a whole lot of time and expense.

bristol299bob 08-03-2012 10:25 PM

Re: Spraying gelcoat
Mast: that's a great write of the process, thanks for the link. It will definitely help

PorFin: Thanks for mentioning MaineSail's excellent how-to. I have seen it but it actually didn't occur to me to try to bring back the original gelcoat on deck. I'll be down at the boat next weekend and take a closer look with an eye towards refinish.

I suspect that most of it will respond well as you suggest. Most of the gelcoat is still quite good. However there are a few areas, particularly in the cockpit, that seem particularly worn. Specifically there are areas that appear to have small pinholes, and these invariably collect dirt and whatnot. I might just do a little hand sanding/compounding in those areas to see if it can come back.

j34035 08-03-2012 11:27 PM

Re: Spraying gelcoat
Follow Mainsails advice step for step and you will be surprised with what you can do with old gel coat. If you do decide to spray gelcoat, buy a gun unless you are only doing small touch up areas. I have used cheap hvlp guns with good results. Wood is a lousy substrate for practice. Do you have an old piece of glass? That gives a good smooth surface to shoot, and you can wash it off after you are done. Thin your gelcoat and set your gun up shooting gelcoat without the hardener and that allows you time to play. The gelcoat will dry but not harden and will wash off with acetone. I have even shot without the hardener on my boat to see color match and then washed it later. Once you add hardner the clock starts ticking. Work on small pieces before you tackle anything like a deck. Good luck with your project!

bljones 08-03-2012 11:28 PM

Re: Spraying gelcoat
The toughest part of spraying gelcoat over a complicated surface like the deck and cockpit is planning your spray plan so that you keep a wet edge and don't trap yourself in a corner. Plan your stop points, and when you think you have prepped enough... keep sanding and filling and sanding again.
IMO prevals are great for touchups, frustrating as hell to do large surfaces. If you're going to invest the time and energy in gelcoat, invest the money for a pair of decent HVLP guns (one will get gummed up when you least expect/want it, so a spare is good), a compressor or turbine capable of the cfms required at the end of 50-75' of non-kinking hose and a swivel chuck, and a decent air filtering system.

j34035 08-04-2012 10:06 AM

Re: Spraying gelcoat
Spare gun is a great bit of advice.

hellosailor 08-04-2012 11:23 AM

Re: Spraying gelcoat
bob, with "body work" the usual suggestion is to buy a hood from a junkyard, or a door panel, and use that as your practice material. You're looking for a smooth finish, and the wood is rough and porous. Maybe the smooth side of a sheet of masonite would do, or a sheet of formica, but I'd aim for smooth and not porous.

When professionals spray, they use different spray guns for horizontal and vertical surfaces. I think we've got some pros on the forum, maybe they'll chime in about this.

But for a whole deck? Considering the fast kick-off time for gelcoat, the small amount a Preval sprayer holds, the fact that fresh gelcoat isn't going to adhere over fresh gelcoat until that has been de-waxed and cleaned...I'd expect to need professional tools, so you can do the entire job in one operation, one pass from stem to stern. With plans to mix fresh batches as needed, and to anticipate any clogs or other issues.

I couldn't extract a clean URL out of this, but there's a Google link to Valspar's guide to using gelcoat. As bl said...planning. And spares.

Gel Coat Application Guide -
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File Format: PDF/Adobe Acrobat - Quick View
Gel Coat Application Guide. Page 1. Introduction. Gel coat makes fiberglass reinforced products attractive and practical. Technically, it is a surface coating of ...

bristol299bob 08-04-2012 12:09 PM

Re: Spraying gelcoat
Doug, bljones, hello sailor: wow, great advice.

I was hoping that I could do small sections at a time but this does not seem viable. Thanks for averting that disaster :-)

I have some spare car body parts, thats a good call. I will be practicing on those. I'll start with a few preval sprayers and then move up to a proper gun (or two ...)

I'm also going to see what can be done about bringing back the original gel coat a la mainsail 's how-to. I that will work for the vast majority of the deck. If so it leaves just the cockpit to spray, a more manageable piece to bite off.

SloopJonB 08-04-2012 12:26 PM

Re: Spraying gelcoat

Originally Posted by bljones (Post 905261)
a compressor or turbine capable of the cfms required at the end of 50-75' of non-kinking hose and a swivel chuck, and a decent air filtering system.

BL, how many CFM do those HVLP guns require? I don't know why, but the CFM requirements of air tools is damned near impossible to obtain. Since it's the air equivalent of wattage or amperage draw on an electrical tool I fail to understand why it is never listed in the specs of air tools.

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