Polyurethane issues when spraying with HVLP
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Toni-mj
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Polyurethane issues when spraying with HVLP

by Toni-mj » Wed Sep 14, 2022 5:18 pm

After numerous attempts at trying to brush the polyurethane Finish without bubbles I decided to use an HVLP spray gun to put on the final coat. I had everything sanded down nice and smooth. Built a relatively dust free spray booth just to perform this task. After I initially sprayed it it looked beautiful. When I returned 2 hours into the dry time I found all of these little bumps, most of them the size of a pinhead that you could only see from an angle, all over the finish. And it's not dust. It literally looks like hundreds and hundreds of tiny little bubbles. I'm ready to give up and paint the door. Does anybody have any ideas on what could be causing this?

This source is guiding me but I want suggestion.
https://holapaints.com/how-to-spray-polyurethane/

The only other input that I can give you is I'm using a husky 40 PSI gravity feed HVLP gun. 20 gallon compressor. I set the tool pressure to 40 PSI and then I have a regulator at the bottom of the gun. When I triggered the gun on the test piece I noticed that the pressure dropped considerably. I had to crank the air pressure on the compressor up to around 75 PSI in order to maintain good output. It was around 50 psi at the gun. I don't know if that has anything to do with it because it was the only way I could get good output. And this is very similar to the defects I was getting when the wipe on poly was drying. It's been a week since my last finish and 24 hours since sanding. Used 10% VM&P Naptha in order to thin the finish.

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