Hi
I Just found some tips on using prevals to spray finnish guitars...I think I will try out on some scraps that I have kicking about will let you know...anyway here are the tips.
Tips on using Prevals
Thinning & Mixing Lacquer
Untinned lacquer is to thick to be sprayed using your Prevals. You must thin out the lacquer with lacquer thinner. Do not use any other type of paint thinner unless you've already tested the lacquer and different thinner out in a plastic cup. If the mixture turns gummy, then toss out the thinner and stick to lacquer thinner as I mentioned. You should purchase a gallon of lacquer thinner. Pour out a small amount of lacquer thinner into a different container to make pouring and mixing lacquer practical. You will want to have plenty availble and it also makes a great lacquer cleaning solution. Once you've mixed your lacquer with your lacquer thinner, you must stir the mixture together. I prefer to put the lid back on the glass Preval jar and swirl the bottle around. Do not shake the glass jar, it will make the solution bubbly and cause the Preval to spit while spraying.
Ratio for thinning lacquer
Try mixing your lacquer and lacquer thinner between these two ratio's 50% : 50% and 33% lacquer : 66% lacquer thinner. Those are the most practical ratio's to use. 50% thinner is good ratio but the finish comes out thick and is harder for the Preval to spray. I prefer a 66% thinner ratio because it will give you a wetter finish. It's easier on the Preval and is easier to spray but tends to run more if your careless. Experiment with different lacquer to lacquer thinner ratio and find out what you like for yourself, it's all a personal perference.
Why does my Preval spit?
The most common problem is a clogged nozzle. Remove the nozzle and soak it in small cup of lacquer thinner. The Preval also may be clogged at the intake valve filter, tube or internally. Fill a small cup up with lacquer thinner and put the Preval intake valve into the lacquer thinner. Shake the tube around to clean out the small filter. Then spray the lacquer thinner from the cup for a couple of seconds to clean up the Preval tube and inside. The thinner will clean the Preval out within a matter of seconds.
The nozzle may be damaged. Do not attempt to fix it by inserting a needle. Just toss the nozzle away and take a nozzle off another Preval refill.
The clear intake tube may come loose. Unscrew the Preval from the jar and push the clear intake valve tube securely into the Preval.
If you shake the bottle you may have air bubbles that will be getting sucked into the intake valve. Let the bottle sit and allow the air bubbles to float to the top of the bottle. Now mix the lacquer by swirling the bottle, not by shaking it.
When you buy your first Preval, you have a choice of two Prevals. One comes with a glass jar and a Preval, the other is just a Preval (cheaper). The difference in price is minimal. I always buy the ones with jars to because they come with a plastic top, this way I can store my lacquer if I don't use it all up that day. You can not use the Preval tube as a mean of storing the lacquer, the Preval tank allows air to seep into the jar. Not only are the Preval jars good for storing, they make clean up so much faster. I fill up one jar with lacquer thinner as soon as I finish spraying my lacquer, I unscrew the lacquer jar and screw on the lacquer thinner jar. I spray the lacquer thinner for a few seconds and swirl the jar, to clean off any lacquer residue off the Preval tube and filter. Then I put Preval tank back on the lacquer jar and leave it there for a few hours until I'm ready to start spraying again. Before I start spraying again, I press the nozzle down for a few seconds to get all the lacquer thinner out of the preval tube and tank. Don't forget to do this or else you'll spray lacquer thinner on your guitar and have an almost instanteous run.