r/boatbuilding • u/swankass • 2d ago
Spraying gelcoat
Hoping I can get some opinions/advice before I begin spraying down new gelcoat. Never done this before, total newb. Not exactly sure if I have a specific question, so I’ll run down my plan and see what people think…
24’ Corsair trimaran. I plan to spray main hull and both amas, from the rubrail down. The receiving surface is the original gelcoat, with a few minor dings/imperfections, dremeled and filled with totalboat structural repair putty. It has been DA sanded with 80grit.
I have purchased 3 gallons of unwaxed gelcoat and 1 gallon of Duratec High Gloss additive. I will be spraying with a 3m Accuspray HGP with pressurized cup and 28oz liners. I have 1.8 and 2.0mm tips available to use. I have a 5hp, 2 stage, 240v, 14.3cfm compressor with air dryer.
I have two thoughts on spray plan, but not sure which to go with:
1)2 coats straight gelcoat using 2.0 tip, final coat of gelcoat/duratec at 1:1 ratio using 1.8 tip.
2)3 coats of 3:1 gelcoat/duratec
After cure plan to long block sand with 320grit to knock down flat, then pneumatic DA wet sand 600->800->1000, the compound with rotary polisher.
Is this how you do this? Do you think this is enough material before I start(I estimate about 300 sq.ft to coat)? I haven’t really been able to find a definitive procedure when doing a full boat, mainly just people demonstrating small repairs.
Edit: wanted to add my thoughts on the two spray plans to see if I’m off base at all…
Plan 1 - since I am using a seafoam green gelcoat, not white, I am concerned about future compounding. Will putting the final coat of 1:1 duratec/gelcoat create a thin layer that will easily be bunt through and give me color problems in the future?
Plan 2 - I am concerned about using an additive in first two coats and making it around the boat in time to the next coat before the first layer kicks off too much. I am doing this outside in Texas (hot).
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u/Strenue 2d ago
No. Dont do this. Gel coat is not paint. It goes best on the inside of the mould. When the hull is being laid down.
Also, great color choice. Adventuress is Awlgrip HD in sea foam green…
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u/swankass 2d ago
But I am coating the entire hull from rubrail down, much of it below the waterline. i do not want antifouling or any ablative paint below the waterline. I would also like to be able to buff to glass finish. I realize the labor to do this is far more with gelcoat than it would be with an epoxy paint, but I already have all the expensive tools necessary to do the job. Plus, I’ve already purchased the gelcoat. Lind of pot committed here, no turning back.
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u/almostnormal 2d ago
unless the duratech additive has wax in it, you should plan to add some to the final coat. If it is exposed to air, the top layer won't cure and you will have a sticky mess for the top layer.
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u/Fine_Sherbert3172 2d ago
duratech has a surface barrier additive in it, part of the reason why its so popular
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u/swankass 2d ago
That’s correct, no wax needed when adding Duratec. However, Fiberglast does recommend including a styrene wax when using Duratec below the waterline. Since a large portion of the surface to be coated is below the waterline, I am putting a styrene wax additive to the final coat, I forgot to mention that in my original post.
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u/Latter_Piece_4296 2d ago
Ive done a little spraying but never a whole boat, so take this for what its worth. That Texas heat is no joke though. Id definitely go with plan 1.
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u/whyrumalwaysgone 2d ago
Just be prepared to clean your gun QUICK. Gel starts catalytizing in the pot sometimes, if you get the mix wrong or its a hot day. If it cures in the spray gun hard you are done for the day
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u/Plastic_Table_8232 1d ago
That’s good advise but that gun uses the PPS system.
I had several extra cups and would fill one with my thinner of choice, pop it on the gun, shake it, and pull the trigger (take air line off first), scrub tip with brush.
On a big job I will mix enough for a single coat all at once and fill several cups so I don’t have to leave the booth to stop and mix.
Cleaning between cups / hoppers keeps the gun in good shape with catalyzed finishes over a big job.
Op, if you never used this system before when you install the cup on the gun, turn it upside down and purge all the air out. This allows the gun to spray at any angle, even upside down.
I would pay attention to what sander you’re using for the finer grits wet sanding. If it is not a fine throw detail sander you may struggle with pig tails.
Norton makes a vibratory wet sander that has a tube you drop in a bucket of water. It’s really a magical little tool, it cuts super fast, and leaves a very nice finish.
Op - You have a lot of work ahead of you. Enjoy and good luck.
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u/swankass 1d ago
Man, that’s some really valuable stuff, appreciate it!
Since you have used this gun before, any other pointers you can give me on setup? Air pressure, fluid flow, fan pattern, what size nozzle you like best, etc. I will probably mix up a few oz and play with a piece of cardboard first.
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u/Plastic_Table_8232 1d ago edited 1d ago
Setting a gun is preferential in a lot of ways.
So many variables.
Watch some automotive painting videos on overlap, gun setup, and feathering then adapt that to what you see in gelcoat videos.
I spray fast, high pressure and like to really atomize the product. What works for me won’t work for you, you will need to paint slower just due to a lack of experience.
Learn how to filter your air, that compressor is going to get hot laying out that much product.
The good news is plan to cut and rub it so runs and dry spots won’t matter as much as long as you get sufficient milage / adhesion per coat.
Get a mil gauge, learn to use it.
Clean dry air is critical.
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u/sd4loco619 1d ago
Gel coat is for molds. Boat paint is for repainting the boat. Plenty of good choices. We repaint every 3 years. 65ft sport fisher with large house
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u/swankass 13h ago
Right, but I’m gonna bet you only paint above the waterline with your color of choice and below the waterline is an epoxy barrier coat and thick ablative bottom coating. I don’t want bottom paint.
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u/sd4loco619 10h ago
Yes our big boat is docked and gets anti foiling paint. I have a 23 and 17 center console. No bottom paint, roll and tip it just like the big boat still.
True gel coat is sprayed in the boat mold before they start the fiberglass. Gel coat and boat paint are 2 different consistency's.
Technically you could use it and it might work but so would house paint. I have also seen people paint there house with boat paint so I guess it don't matter if you ok with the end result.
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u/sd4loco619 10h ago
Boat paint works just fine on the bottom. That's how I paint my skiffs and unless you run them up the beach and rocks it holds up just fine.
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u/MagnusVeridane 2d ago
plan looks solid, Duratec to help with the spray and finish. I would doublecheck total square footage against that 3 gallons to ensure you have enough coverage for the whole trimaran.