Question
We need to spray a solvent based dye stain on white oak in a production project. Does anyone have advice? We have tried HVLP guns and HVLP through a turbine. It's pretty tricky to avoid striping, and it's complicated by the stuff totally changing appearance once the finish is put on. I think we need to do two light coats, but we need to keep the color light. This material is new to our finish guy.
Forum Responses
I'm certainly not an expert, but I have had some experience with alcohol based dyes. The stripy-ness can be a problem, especially if you spray it on as if it were a wiping stain. The way I've dealt with it is to turn my fluid level way down and fog just the right amount of dye on each piece. It may take several coats to achieve the right color, but it usually only takes a few seconds between coats to dry. Each piece sort of needs to be treated as an individual, which is a different mindset than flooding on a wiping stain and just wiping off the excess.
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.
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.
Where you say you're doing a light color, spraying your stain just to where it looks wet usually gives the best result - especially on oak. You certainly don't spray it like you would a wipe stain, but just to where you can see that your wood is actually getting wet. Make sure that your passes overlap properly, and you should be good.
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).
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.
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:
- knowing your percent of solids by volume
- knowing the viscosity of your material
- knowing the fluid flow of the gun
- knowing how thick your wet mils of finish are
- knowing how far to hold the gun from the surface
- knowing how fast to travel with the gun
- maintaining the same temperature and humidity in the finish room (adjusting your finish's viscosity accordingly)
- doing the same finish schedule to every surface, including the sanding sequences and order in which things are done (following the finish recipe to the letter)
