MIMF

Hey guys
I'm finishing my second project, and started painting with rattle cans.
I'm going for a black les paul.
I've done about 7 layers over 4 days, but I got some paint runs on the last pass.
How long do i have to wait before I can sand these out?
I got my hands on a old compressor and spraygun half way into the project. Is it ok to move from rattle cans to a spraygun on the same paint job?
if yes, what should i keep in mind?
Thanks
Gerbrand

You should be able to level down the runs (I use a razor blade) and block sand the next day after spraying assuming normal drying conditions and no complications.

It's hard to guarantee compatibility between lacquer brands, but typically, most of the time, it is not a problem to go over one with the other. There is a risk, but a minor one. Probably won't know until you try it. If you have some of the rattle can left, test it out on a piece of scrap. This will at least reveal any immediate incompatibilities, but not long term.

I would say that the next day is too soon to flat out runs, If you can make an indent in the finish with your fingernail then it's too soon, you can try with a piece of fine abrasive paper and you'll soon know if the paint has hardened enough, it really depends on what type of paint you're using, cellulose takes quite a time to set hard. A good tip to remove runs (as well as using a block) is to use a Stanley knife blade and wrap two pieces of Scotch (3M) tape over the cutting edge but leave a gap about as wide as the run and then scrape the run away, the tape will protect the surrounding paintwork, then finish off with a small block and abrasive paper, something around 400 grit.

As for swapping to a spray gun, definitely try on scrap first, you really DON'T want to risk a reaction.

I've had incompatibility even with different brands of solvents and lacquer, so I don't reccomend changing the method/product on the same finishing job.

About the runs, if they're not REALLY bad, I just ignore them, keep applying the coats and leave the final leveling to the sanding/polishing process. If it was the final coat, I wait the full curing time to sand them flat. That's just how I do, but I should mention that I got factory glossy finishes this way.

My preference is to remove runs as soon as possible so that the remaining coats will be as smooth as possible. The excess lacquer in the run cures more slowly and will continue to shrink for a long time and you may end up with a low spot if you leave it till the final leveling.

I never had that problem.

@Henrique: How did the incompatibilities manifest?
I've sanded the guitar down to a nice level but in some spots went all the way to the wood again.
I'm really keen to try the spray gun but would like to know what to look out for on my test pieces
Thanks
G

In my case, unfortunately late. A few weeks after sanding and buffing a white haze appeared on many spots. Nothing to do with "blushing" during the coating process. It happened to four instruments. Too bad the only solution is to strip all the bad finish and start over...

Ok I sanded all the rattle can lacquer down and sprayed with 2k automotive paint.
The problem is I have no experience with the stuff, and the people at the paint store didn't tell me about hardener.
I just thinned it with lacquer thinners and sprayed.
I sanded out the orange peel after 2 days, and it seems dry, but will it ever harden?
Can I spray another coat mixed properly with hardener over this first coat, or should I sand it all down again?
Thanks
G

2K automotive paint IS NOT LACQUER. Paint stores are notorious about providing poor information. They know their products but often know nothing about traditional finishing materials.

Since you did not use their hardener, it will probably never cure.

I would call the company and ask to speak with a tech. Hopefully that person will have some advice about removing the finish.

this is a last ditch effort before stripping, but I have done it successfully with conversion varnish. Spray on a mix of hardener/catalyst with lacquer thinner or a mix of lacquer thinner and butyl acetate, which will be a bit slower drying and hopefully give the hardener a chance to react with what you've already laid down. If you use Butyl Acetate you only want to have maybe a 20% to 80% LT ratio, and use a small amount of hardener. I can't guarantee that this will work for your product but it might be worth a try.

Thanks for the replies
I've leveled out the orange peel and I've taken much of the paint off in the process.
Do you guys think i can blast a layer or two of paint with allot of hardener mixed in to harden the bottom layer at the same time, or should i try to just spray some hardener first, and then normal 2k+hardener?

I must say the stuff is harder after 3 (without hardener)days than lacquer was after 2 weeks
G

Hardeners are there to induce rapid cross-linking of the finish. The fact that you can sand it is good news. Get it back down to wood and don't worry about trying to harden it after the fact. You might be fine going ahead but you might also end up with adhesion problems later on and waste a lot of time and material in the meanwhile.

from experience I alway use one brand of nitro lacquer products Behlen/mohawk. This keeps it simple. I always use there solvents. Make sure you dont introduce silicons into the mix by using sterrated sand papers or flo out. dont use resin cloths.. never use big box store lacqure thinner, even in a pinch. Note. the behlen/mohawk you buy in california is not the same voc and solids make up, as most other states because of epa rules there formula has been changed.

So the paint job is finally done.
Thought I'd share a pic

Looks very nice.

rattle can spraying always needs extra time for drying and gassing out Id wait 3 days then razor blade scrape the run before any sanding dont use sterrated sandpaper it may introduce silicones, thats bad. I never spray anymore than 3 coats on a nice dry day good luck.

Look's great!