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Cygnus A

Fuji HVLP for Gelcoat?

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I have a Q5 that I use for a lot of different things. My brother does a lot of fiberglass work and likes my gun, but isnt sure it will be capable of spraying gelcoat finishes. He has an HVLP gun he runs on a compressor at 40psi and it works just fine. We are trying to determine the difference between a compressor powered HVLP and a turbine HVLP. 

Will the Fuji work for this application? 

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Well I'd check 2 places. The finish company might suggest a tip for best application. Second Fuji will probably be able to tell you yes or no. My guess is yes. First Pressure doesn't mean as much as some people think. 40 psi through a 1/4" line could be a LOT less air than 12 psi through a 5/8" line. Fluid dynamics with compressible fluids becomes tricky so your gut reaction my be right but may not be, best to consult the pros.

The tip size can give you a clue if it calls for a tip size fuji doesn't make that'd be a red flag.

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Chestnut has some good points. I would be concerned about the viscosity of the gel coat and the drying time. If it dries quickly by using a catalyst remember to clean the gun immediately. I've never used gel coat so I can't be much help otherwise. Also ask about temperature sensitivity. A turbine puts out hot air which can accelerate drying times. A compressed air conversion gun uses a pressure drop to create the HVLP affect which might actually cause a temperature drop , I'm not sure but definitely ask about it.

If a catalysed finish starts to dry in the gun it can be a nightmare. Ask questions and be prepared. Have the appropriate brushes & solvents on hand .

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To spray gelcoat, you have to thin it with Styrene.   The biggest worry is it kicking while it's in the gun.   I use an old Binks no.15 regular spray gun for small repairs, because it uses a leather gasket for the cup.  I didn't want to experiment to see what other types of gaskets resist styrene.   

There are two types of polyester gelcoat.  One has wax in it that is supposed to float to the surface for curing, and the other type doesn't have the wax in it.   You can spray a nicer finish with the non-waxed one, but you have to cover it with PVA for it to cure hard.   It will kick, and cure without protecting it from the air, but it won't buff off very well.  One of the disposable Preval sprayers is what most people, including me, use for the PVA.  The PVA just washes off with soap and water before you wet sand it, and buff it.  You can get a high shine if you cover it with PVA, but not without.

Don't even think about spraying it without styrene.    I'd buy one of the cheap HVLP guns off ebay, and if it gets clogged, just toss it, but that's actually what I bought the 15 for, back when I was a teenager in the late '60's.

I used to own a boat shop, and did repairs all the time, but I have only ever used conventional spray guns for gelcoat, just because that's what I've always used, and the guns are still good.   I don't know that there would be much difference between a tubine rig, and a conversion gun.   I don't know of any autobody, or boat shop that would use a turbine rig, but I'd never spray gelcoat through a Sata gun.   If I did it all the time, the most money I'd put into a spray gun would be one of the lower end ANI guns that you can get for less than a couple of hundred dollars.

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I watch Andy a fair bit due to the fact that I was working in a boat a short while ago. It is nice to read Tom’s post as his commentary explains some why behind Andy using PVA. 

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I'm still doing it the way I did back in the '80's, but it looks like there are other things available now.  Styrene may even be illegal in California now.  I was a Hobie Cat dealer then, and I don't know if they even make boats in California now.

http://www.fiberglasssupply.com/Product_Catalog/Gel_Coats/gel_coats.html

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