Spraying Gelcoat

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DanielR

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I am considering shooting fresh white coat of gelcoat on inside/outside of a boat. I've decided to make separate thread to cover that topic. My built, 1992 19' Maxum, can be found at http://forums.iboats.com/showthread.php?t=446612

I have painted cars and did body work (not professionally), so Im familiar with spraying process. I did work on fiberglass before, doing molds of subwoofer enclosures/mirrors/etc, but I never sprayed the gelcoat.
Since I will be doing the interior I want the gelcoat to match inside and out. Knowing that outside yellowed due to many years of exposure, it has some cracks and nicks. I rather respray it than try to match it. I'm redoing whole interior, might as well do it right.

Questions I have:
1. What gun tip do I need to shoot the gelcoat, and what would be best way diluting it so it goes through the gun?
2. If I spray it over existing gelcoat ( say sanded down to 400grit) how many coats is recommended. Or, is it better for me to sand it as much of existing to avoid buildup and future cracking?
3. What is the recommended body filler for marine applications?

Thanks
 
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DanielR

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Re: Spraying Gelcoat

I've read that as well as the link in the thread you posted.
I am familiar with compounding/detailing.

In all those posts conclusion was to 'properly' restore the gelcoat condition which is not a case in my situation.

I am re-doing interior and everything inside will be painted/gelcoated. Since the outside gelcoat darkened i do NOT want new paint be matched to old finish.

Number one reason I am considering gelcoat over paint, is that paint is much harder to repair.
 
erikgreen

erikgreen

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Re: Spraying Gelcoat

Well, I'd recommend you read up on the whole process for a number of reasons. However, to answer your questions directly:

1. You need a different gun to spray gelcoat for the most part. Gelcoat is thicker than any paint you've ever used. You can buy a "gelcoat dump gun" that is basic but works well for about $150. The tip will be about 4 to 7mm wide. The guns actually can double as basic sandblasters for small areas.

The other benefit of the dump gun is that it works using a disposable paper cup to hold the resin. Assuming you don't spring for a auto mix gun, this is important, because one batch of gelcoat that kicks off in a regular gun will ruin it. Further, the innards of a regular gun may be ruined by contact with uncured gelcoat. Not too likely, but possible.

You can thin the gelcoat enough to shoot it in a regular gun, but that will reduce its properties so much you might as well just skip it. Ideally don't thin it at all.


2. You don't put on a specific number of coats, but rather you use a gauge to measure the thickness of the coat. Too thin and it will sand through easily when you smooth it, too thick and it'll crack. Most gelcoat brands want a thickness of .01 to .02 inches. Use as many passes as are needed for this. Keep in mind you must work fast because the resin will start to cure as soon as the catalyst is mixed in. Spray enough thickness that you can sand off gelcoat to get a smooth surface.

3. Use a vinylester body filler for below the waterline work, or an epoxy one. Bondo has a marine filler that can be used below the waterline. Most of the "ultra lightweight" auto fillers can be used above the waterline, although if you're going to the trouble of re-gelcoating I'd use the good stuff. You can also fill in holes with fresh glass, and putty with a mixture of epoxy or poly resin and microbubbles (cheapest, and works well).

Plan on a lot of sanding the gelcoat to fair it, plus at least 3-4 passes with finer papers and wet sanding to get the final shine. Gelcoat is considerably harder to sand than auto paint (except some of the very best auto paints). See Oops' "Hull Extension" thread for details.

Also plan on sanding the old gelcoat and cleaning it very thoroughly with a dewaxing agent plus acetone or xylene. Any contaminants will cause you problems.

If you use a non stock color be sure to record the mix so you can duplicate it for repairs later on.

Good luck,
Erik
 
Yacht Dr.

Yacht Dr.

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Re: Spraying Gelcoat

Gelcoat is actually Very ez to apply. IMO way easier then paint.

What you need is for full gel spray...

1. repair as needed. prep with 80-120 grit.
2. mask and tape.
3. acetone wipedown.
4. Mix Gel ( Im assuming white..this is NOT for dark colors !! ) with approx 20% Patch Aid and About 10% acetone.
5. Mix MEKP catalyst about 1.5-2 % ( depending on the gel.. ).
6. Start spraying ( H.F. 2 qt pressure pots work just fine ).
7. Spray 2 medium coats then Flush gun with acetone.
8. Mix more gel and spray 2 wet coats.
9. clean gun. have a beer.
10. Get a Big magic marker and goto town ( kids love this part ) . just scribble all over. then a damp acetone rag to Smear it around making a good guide coat for sanding. ( you can use dykem or etc instead but this is cheap and fun for kids marking smily faces on the boat :) ) .
11. Block or DA sand with 320 or 400 depending on how well the gel layed down. ( Dont sand all the guide coat off .. just about 90% ).
12. wetsand with 600 untill the rest of the guide coat is gone..then again lighty with 1200 grit wet.
13. Buff till its done.

I know this sounds alot..but If you want a step by step on HOW to Paint..the list and steps goes even further.. with no room for messups :) .

GL .. YD.
 
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DanielR

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Re: Spraying Gelcoat

Resin will need to have surfacing wax from the beginning?
Spraying coats would be wet on wet, or should I wait certain time.
It's 19' bowrider, it doesnt have that much surface so spraying it should be matter of minutes.
I imagine getting gun with 2.0 tip would be plenty for gelcoat.
 
Yacht Dr.

Yacht Dr.

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Re: Spraying Gelcoat

Tack coat..wetcoat then recoat as needed when the wetcoats are Just kicked off enough not to run.

You can use the finger tip method on your tape line. If its WET..then not time yet :) . It depends on how you reduce it as to when to recoat.

You would want to reduce JUST enough to spray with minimal orange peel. Flowing gel like paint cannot be done..

You might just want to skip the wax and spray PVA over the gel when its tacked off. WARNING WHEN USING PVA = clean your gun with acetone..then WATER..spray PVA .. flush with WATER then flush with acetone. DO NOT use acetone and PVA together. It will turn to snot :) .

YD.
 
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harmonpa

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Oct 23, 2017
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I would agree that a pressure pot will work well for spraying smaller amounts of gelcoat. If your going to do a whole boat may make sense to look at an option that will mix the catalyst at the gun tip. Go with a conventional spray gun because gel coat is pretty thick and may not break well with HVLP.
 
89 resorter

89 resorter

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I am in process of re-gelcoating the hull of my Century Coronado and I found the below link of great help. I basically decided to go through the extra work for peace of mind since I plan on keeping the boat in my dock for months at a time and felt it would hold up better than paint. I tested this process on an old dock box lid and it worked out really nice so I am currently at the point where I have applied the first three coats on the boat hull and began sanding to remove orange peel and fairing. The best of luck with whatever process you decide to use.
 
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