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Guitar Refinishing...Car Sprayers?

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clear coat
2K views 11 replies 6 participants last post by  littlegreenman 
#1 ·
Not thrusting many of the so called refinishers around here, i was thinking of the possibility of refinishing a guitar at a car sprayer's shop.

I think they usually put the cars in a big oven, does that mean a guitar will get baked too?

I'd imagine that the finish would be quite nice.
 
#2 ·
You wouldn't want them baking your guitar, but it is my understanding that if they are using heat to cure their finishes, then if they don't bake your guitar, it just takes longer to cure. But it doesn't mean that the finish never gets fully hardened. There's an ultraviolet curing method that I'm not familiar with, but it is done in some guitar factories and doesn't use lots of heat. Perhaps that's what they are doing, and in that case, by all means, allow them to do it to your guitar. The only thing about car guys is that they aren't used to getting finishes as thick as on guitars. A car body doesn't absorb any finish, and it takes far greater force to dent a body panel, so the finish does not have to be a protective shell around the car. On a guitar, it has to have strength in and of itself, so it needs to be thicker. Car guys often lose patience, and re-coat too soon, so you can get a soft or rubbery finish. As long as they are open to it, you should have good results.
 
#4 ·
I'm not sure I follow you, what exactly wouldn't you tell him? His guitar looks great. He did all the sealing and leveling himself, which is a great idea. That way you give the car guy a flat, fully prepped surface, more like what he's used to. Its the filling and sealing that's the big difference between wood and metal. It sounds like Keith is thinking of using a car shop for the whole job, not just the clearcoat.
It's a pretty well known fact that excessive heat isn't good for the wood. It can weaken glue joints, and encourage premature cracking. It's different during the Kiln drying process, because you are drying an entire length, before joining and carving. It's like leaving the guitar in your trunk during a hot summer day. Its just not a good idea. I'm sure baking the clear coat didn't hurt his guitar, and it looks great. I just wouldn't recommend it unless you have to.
 
#5 ·
an automotive drying tunnel is generally only 60C anyway, that wouldn't hurt wood to bad, still wouldn't really recommend it, but alot of shops are baking with ultraviolet light now or infrared, can't remember, but the heat is very minimal.

I'm not sure why you would get a rubbery finish either if they spray too soon. The reason for leaving the flash time between coats is because the Poly will flow so much if you don't allow for that flash, you will run and build up to what will take days and days to cure. If they flash time (usually 25 to 30 minutes is allowed) the finish cures in about 20 hours and the new coats will melt into the previous without flowing out to much.
 
#7 ·
I don't know what kind of finishes they're spraying in Malta, so I figured I'd get all my warnings to him out in one swoop. It's my understanding that with a urethane or a 2 part catalyzing finish, it will eventually cure even if the top coat(s) flashed over before the undercoats were dry. But you're right, they would cure eventually. That's what I mean when I say rubbery. You could finish the guitar and assemble it because it feels dry, but the neckplate and hardware still make indentations over the first few weeks or so, because it's rubbery underneath. But acrylic car lacquers can do that too, like nitro, right? If you shoot them too heavy the top coats can trap solvent underneath and prolong the curing time.

It was my understanding that the UV curing allows for a much thicker, much quicker application because the UV cures it to the core in a few hours or so. When I was at Cor-Tek they had just upgraded, and they were marveling about how you could have a guitar go from raw to totally finished in no time at all. But I think with some UV cured finishes, if you don't UV cure them, they never cure. Does that sound right? :?

If they're baking the finish with just heat, is that actually causing a reaction? Or is it just speeding the evaporation of the solvents? I thought it just "speed-cured" it, and that's why without the heat, you had to wait much longer, but the finish would still cure.
 
#12 ·
In a 2 part finish, like Poly Urethane, or even Epoxy glue for that matter, it cures with a chemical reaction, hence the 2 parts ;)

Anyway, when these products dry, they are actually heating up. Mix up a batch of epoxy in a plastic cup and just let it cure, when it's at that almost hard stage, feel the bottom of the cup, it will be hot. When you heat that paint, or epoxy, you are causing the reaction to occur more quickly, it's not an evaporation of solvent like in the case of laquers. It is the acceleration of that chemical reaction :)
 
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