Spraying Dye Stain
Also, I keep my finished control sample handy. In the few seconds it takes for the dye to dry, you can get a pretty good sense of what the color will be when the clear coat goes on.
Because I tend to be paranoid, I also spray a few test pieces as I'm going along to spot check that I'm not getting too dark or too light. I let these dry for the 30 seconds it takes me to refill my coffee cup, and spray them with rattle can Deft. This will bring the color out and allow you to gauge how you're doing.
I thin my ngr with 50% thinners to avoid the striping. I also spray each piece from four directions to get in every corner. Turn down your air pressure to avoid bounce out. Take the time to do a couple of samples and you should be okay.
Perhaps you need the right equipment. I would use a Kremlin PMP150 (double diaphragm pump) with a M-22 gun. You could even add a reciprocating line to prevent any settling or separation. This would provide you with a system that has no pressure fluctuation.
Turn your fluid pressure down and your air pressure up to around 45-50psi. Run a couple sample pieces through the finish and you'll be fine.
I've been spraying dye stains for a couple of years now, but at first I had a lot of the problems you are talking about. I actually mix up my own stains using Sherwin-Williams dye concentrates, a little vinyl sealer, and then a mixture of acetone and n-butyl acetate for the solvent. I haven't actually tried many pre-made dye stains.
When I first started, striping was one of my biggest problems. This was usually due to a faulty gun. Either one side would spray slightly thicker than the other, or the edges would spray thicker than the middle. This can often be corrected by adjusting your air pressure (usually 50 psi works about right.) You also need to make sure your fan width isn't too wide - the less fluid you're sending through the gun, the smaller the fan width should be.
I also had the problem of having the wood change appearance after the finish was sprayed on until one day I was watching a finish man at a large cabinet shop in our area. He'd take a sample and spray it with his stain. Then he'd cover half of it and spray the other half with a clear coat. This way, he'd have a sample showing how it should look with just the stain on the wood, and with the finish put on. He'd also keep that piece right close so he could make sure he was getting the color correct. You have to be careful with dye stains because just spraying it on a little heavier gets you a darker color, so having a sample to reference off of is all important.
These are just a few things I've learned the last few years. Dye stains are a little tricky to get used to, but once you learn how to use them, you'll never want to go back to a wiping stain. Also, I should mention that a dye stain produces absolutely beautiful results on maple, where a wipe stain on maple practically ruins the wood. (Of course, some people like this look, but...) I've been spraying all these stains with just a pressure pot system with a decent spray gun (which is starting to get old and could use a replacement).
All the advice given is accurate. You might also try adding a little retarder to your stain to give you more time to see how even your color is.
If you make a mistake, all is not lost. If it's too dark, you can lighten the color with a few strokes of red Scotchbrite pad. If it's too light, restrict the fluid and air on the gun so that it makes a mist, and gently puff the stain on the light spot. I've been spraying dye stain on pianos for years this way, with excellent results.
Making a step sample is a great way to see if you're on track with the stain color. Do your sample and after each step, tape off a 2" strip. When completed, you have a sample that you can check each step of the way to assure consistent results.
One method is to add that tiny amount of dye stain to a toner coat of finish. The finish is reduced to 50/50 or is reduced even more and the dye is added. If you have problems with striping, this method may not work, because it is designed with production in mind as a one pass system, overlapping by about half.
I am going to try the gun adjustments mentioned here because even though I have an Asturo, I still get striping, one side of the fan seeming to be heavier than the other. Maybe the very thin nature of the dye stain is taxing the needle/nozzle/air cap, which are supposed to be used according to the viscosity of the material I am using.
So much of this stuff is trial and error, unfortunately. The more we can do to get the math in place, the better. That means:
From the original questioner:
I really appreciate all the sharing of experience here. Against my advice, they wiped on the stuff thinned way down, and there are stripes visible to my eye, hopefully not the public's.
I have had good success using a mini HVLP with the fluid flow at a bare minimum. Fogging by eye is effective with a small volume of work, but I suspect wouldn't be cost effective in a high production environment.
Spraying dye stain is basically the same skill as shading or toning and the way I teach that is to get a 2' square piece of white melamine and practice spraying an even, white tone over the entire panel. Any streaking will be apparent right away and you can work on your technique until you get it right. Then, when you tone wood, if you just go in the direction of the grain with a nice, even pattern, you will never know the piece has been shaded.
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