Uneven spray from nitrocellulose aerosol can

[Andrew Noble]

I'm putting the finish on an ash solid body with Behlen Stringed instrument nitrocellulose lacquer in aerosol cans. The can and ventilated room are at the right temperature (I think - 22 celcius) and I shake the hell out of the can first, but the two cans I've tried still spit out lumps occasionally. Have I got an old batch or what? I'm wiping the little lumps off and after another coat you can't see where they were, but this can't be right can it? The vinyl sealer didn't spit lumps. Any advice gratefully received by a first time guitar builder.

[John Sonksen]

Just went through the same thing, wish I had an answer for you. I'm going to be doing my topcoats with an actual spray gun though to try and avoid this. I did periodically turn the can upside down and spray it while shaking in a feeble attempt to get the can to release these boogers. It would work for a minute and then splonk! another batch of chunks. My nozzle looked clean and the size and amount of chunks wouldn't be explained by buildup there anyways.

Even when it wasn't blowing chunks I can't say I was a big fan of using these, the tiny spray pattern with random atomization
and the inability to adjust the thin-ness of the lacquer were huge minuses for me. I ended up with runs all over the place and had a really hard time getting a nice wet coat. After what should be about 6 coats on mine I'm unsure how many I actually have on there, since I was being more and more skittish about going too heavy with the lacquer. When I went to level out some of the chunks and runs I ended up with several sand-through's which I wasn't happy about to say the least.

I bought a spray gun from harbor freight for $15 (a little less than the cost of two rattle cans of lac), and a quart of
un-thinned lacquer, and am going to go from there.

[Mark Swanson]

If you have a bump in the lacquer, let it dry and then take it off with a razor blade used as a scraper. Scrape it about 75% off, then wetsand just a little and later coats will cover it just fine. You can do the same if it's in the final coat, you just need to scrape it down a bit more and the wetsanding will take care of the final bit. If you do just try and wetsand them off you will go through.

[Andrew Noble]

Thanks for the advice guys. I've been persisting with the aerosol cans and I've found lots of shaking to begin with, and then shaking for a few seconds between each pass seems to almost completely stop the problem. Swearing seems to help too. The shaking all the time does make it hard to get an even coverage. You need the light just right so you can see exactly where you're up to but it does work. I think for next time a spray gun is the way to go. Does anyone have an opinion on HVLP vs the old school compressor and gun? Thanks again.

[Clay Schaeffer]

The main advantage of HVLP is more efficient transfer of finish to the product - less waste of material. For occasional finishing a "conversion gun" which also requires a compressor might not be a bad choice. Some conversion guns are relatively cheap and if you find one in a "jamb gun" size so much the better. The compressor need not be a large one for spraying guitar sized objects (as opposed to car sized objects) so the total cost may work out to much less than a decent turbine type hvlp. Harbor freight sells a cheap turbine type system which works O.K. for lacquers (thin bodied materials) but puts out more material than needed for spraying a guitar. Also the plastic parts need to be cleaned after spraying each time.
I use a cheap high pressure jamb gun and a small compressor. It works O.K. but does waste some material.
Another alternative is to use brushing lacquer and good technique. Brushing lacquer is not hard to find ,but good brushing technique is becoming a lost art. <g>

[Chuck Raudonis]

Try warming up the can of lacquer in a bowl of hot water before spraying. Seemed to help me.

[David King]

I use the HF conversion HVLP jam gun which goes for about $60 ($40 on sale). It works reasonably well but the controls are easy to nudge by accident as you are spraying so I'd recommend marking where they should be set with a sharpie and taping them in place until you are ready to clean the gun. A small, oilless pancake compressor should have no trouble keeping up with that gun which only uses about 9CFM max and closer to half of that when you are spraying something small and intricate like a guitar