[Quickstep]

I've just started spraying waterborne lacquer and although I'm committed, I'm having a bit of a struggle. It doesn't help that I'm new to spraying in general.

The stuff I'm spraying (Grafted Coatings KTM 10) seems relatively thin, (10 seconds in a ford cup), but I think I'm getting thrown of by the higher solids content. Plus, the stuff dries so fast that it's hard to tell how wet to make a coat. Seems like no matter what tip I try or where I set the pressure, I get micro bubbles in the finish. I get the same micro bubbles when I brush the finish, but they're gone the next day. When I spray, the bubbles appear later in the process, but they don't go away. I'm looking for pointers on tip selection, air pressure and technique. Everything I've read says not to thin the finish.

I'm using a DeVilbiss Plus HVLP gun; they recommend 26 psi at the gun (with the trigger pulled). My compressor has no problem achieving that, but it feels like a lot of pressure. Also, with a 1.3 or 1.4 tip, it seems like it's dumping a lot of material on the surface. The coat seems too dry with the 1.2 tip. I'm spraying test coats on a horizontal surface, so for now, sags and runs aren't an issue, but I know that will come if I don't resolve some of these more rudimentary issues.

Any insight is greatly appreciated.

 

[cabinetman]

Try this. With HVLP it's difficult to see how wet your path is. Try to use a lot of light to get a "glare". A 1.4 should be adequate. Thin about 5% with water (as a test). Adjust the gun between 10-15 PSI, and about 35 PSI to the line. You may have to fiddle with the air/fluid mix, and your pattern. Spray on a sample and see what it looks/feels like.

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[Steve Neul]

Usually when you get bubbles in a finish it is because you are putting it on too thick and or the finish needs to be thinned. It can also happen if you have the sprayer too close to the work. There should be about a foot between the nozzle of the sprayer and what you are spraying. For wood finishes I would use a 1.8mm tip on the sprayer. It would be difficult to say what air pressure because each sprayer works a little different. I use a cheap harbor freight sprayer and they work best at 40 psi. Also temperature and humidity can affect the finish. There should be a temperature range listed with the finish and if you are working it too cold or too hot it can give you a lot of trouble.