Troubleshooting Micro-Bubbles in a Water Based Finish

Another case of tiny bubbles, solved by dialing in the "right" air and fluid pressure settings. March 1, 2006

I seem to be having a problem of late with micro bubbles in the water base finish I am using (Compliant Spray's Enduro). I am using the conditioner they have for flow out. I have the air set at 20psi with the gun triggered and fluid at 10psi; and Im using a 1.1mm tip. I don't know if it's the speed of the strokes or what but it happens more in some places than others.

I don't think the coats are too thick - the bubbles look like what would be solvent pop in a solvent based product. I have looked up in the books I have on spray finishing and tried the recommendations but can't seem to get it right. It's really putting a damper on getting this stuff finished. Any suggestions would be much appreciated.

Forum Responses
(Finishing Forum)
From contributor R:
Could it be that the size of the tip is too small?

From contributor B:
What type of spray outfit are you using - AAA, pressure pot or a cup gun?

From the original questioner:
I am using a pressure pot setup with an LVLP gun. The tip size was recommended by the finish supplier and I've had no problems before. My guess is that I just have the air pressure dialed in wrong since I added the conditioner - it probably thinned the finish somewhat and I need to back off the air.

I have two setups like this and it happens with both. I figure someone else has had the problem and I could save myself some grief going through all the possible choices I've come up with.

From contributor N:
Lower your fluid pressure by .5 to 1.0 psi. This might make a big difference in the removal of the micro air in the pressurized finish. Being as you thinned the product you should then lower both the fluid (pot) pressure and the atomization pressure. Secondly, apply thinner wet coats. Stay within the 1-2mil wet film thickness range. This works well for me with all of the WB's that I use. Last - call the manufacturer and review the situation with them.

From contributor B:
I also use Enduro, and have run across the same problem. I use accuspray pressure assisted gravity gun with 1.1 tip with a wide fan air nozzle. I started getting the bubbles when I switched to spraying horizontal for my second and then final applications. The problem was I was spraying too heavy. I adjusted the fluid way down (right at 3 turns on the accuspray) and sprayed with slower passes. The product was atomizing better and lay down like glass, problem solved. The only time I ever get bubbles now is when I don't pay attention to my fluid setting. I also always use 10% conditioner

From the original questioner:
I played with it some more and think I have it dialed in right. This is why I hate finishing sometimes. You move one knob a 1/16" and it throws things off. I switched one gun to a bigger tip - 1.5mm and dialed down the fluid pressure to 7psi and the air to 19psi with the gun triggered. It seems to work much better than the before though the humidity is way down today which always has an effect, no matter what the suppliers say.

From contributor R:
I spray a lot of Fuhr 355 acrylic varnish and have made the mistake early on of shaking instead of stirring. The other times I've noticed it is if I use shellac as a sealer and to pop the grain and topcoat too soon.