Question
We are using a Kremlin airmix 10.14 pump and for the most part are very satisfied with the results. But one problem keeps coming up. When spraying cabinet doors flat on a bench, we notice small air bubbles in the finish when wet. Most lay down when it flashes off, but some are still noticeable when dry. We use Sherwin Williams CV reduced 15% with xylene, an 06 tip, and air and fluid pressure at 10 and 50. We have tried different pressure settings with the same results. Any ideas?
Forum Responses
I shoot a lot of SW Con-Var. I have the same problem. I have had better results if I cut the first coat by 50% with xylene or, in warm weather, with High Flash Naptha (to slow flash time). Second: a lighter first coat (spit coat) followed by a full sanding. 220 grit also helps.
Lisa Gilbert, forum technical advisor
One other thought regarding a 6 tip. You can remove the tip filter screen and go with a higher mesh gun handle filter.
I use the same unit when I spray pre-cat or conversion varnish products. Only difference is I use other name brand products. Not only do I have one of the systems, I have sold this same system to quite a few cabinet shops in my area. I teach each shop how to set up and maintain their systems the same way.
As for taking the screen out of the #06 tip, it will still have a smaller orifice than the #09 tip. To me, with the higher solids of CV's, it's like trying to squeeze an orange through a straw. You can change the screen at the end of the gun to help strain the paint before it goes through the gun.
Lisa Gilbert, forum technical advisor
Comment from contributor A:
I work for a large custom cabinet manufacturer, and we have about 35 or 40 Kremlin Airmix guns (automatic and handspray), as well as other brands. The problem you describe is air entrapment or air entrainment. It results from the microfoam that is generated during the atomization process at the tip. Air-assisted airless is particularly troublesome for this; we sometimes experience it too.
Things to look for include keeping the atomizing air as low as possible, just enough to break up the "tails" seen with no air. Also, be sure that your substrate is at the proper temperature. Atmospheric conditions have much to do with this problem, especially hot, dry air which promotes rapid surface-cure; this is why slowing the coating helps. I am concerned that cutting solids as much as I've seen recommended here will rob build. I'd be more comfortable with a smaller add of a slower solvent such as Butyl Cellosolve, n-butanol or isobutanol, or even 2-ethoxyethylpropionate (EEP). A few ounces of any of these will slow the dry and should help. Obviously, cutting the solids drastically works, too.
I am a chemical engineer, and worked for paint manufacturers for the first 13 years of my career, and now 7 on the user side, and have battled this issue many times. You may also want to inquire of your SW rep if they have any kind of bubble breaker available, but be cautious with these. They are, by their very nature, somewhat incompatible and in some instances may cause or intensify a fisheye problem.
We recently expanded our operations into a new, larger industrial complex with a completely new spray department installed, all new equipment. However, immediately after beginning operating there, I noticed that some of the finished product was exhibiting the same small air bubbles you described. My first thought was air entrainment, and this evidently was indeed the culprit. The problem was the final coat of (pre-cat) lacquer was flashing off too soon - as the gasses released, forming the bubbles, the material wouldn't settle out.
I believe this could be what is causing your problem too, from the way you described it. At any rate, it's something to check for and is certainly an uncomplicated solution. I also concur with Lisa Gilbert - you might be better off with the 09 tip for final coat, which is what I use (09.094 for the wider fan width). For the pump settings, I set the gun air regulator (grey knob) to 15-20 psi and the fluid air regulator (red knob) to 50-55 psi.
The first thing to check when you have trapped air bubbles is if you have air in your line. Sometimes that happens when you are getting low in product and then your pump is pumping air and then you add more lacquer. If you don't flush your line until the air is all out you will always have air in your line.
To know when the air is all out is simple. When the lacquer is coming out of the gun (without the air cap on) and it is clear then you are good to go. If it's a really humid day or a really hot day I would recommend to add about 5% eep or buttylcellusove into your lacquer that will slow it down and that will give the solvent time to escape before the top of the lacquer starts to dry. Also, don't forget to check your wet mill once and a while. It should be between 4 and 5 mills. If you are checking all those things you should not have any more problems.