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Hi guys,

I was painting a practice panel over the weekend, just to see if I liked a particular color. The surface was primed with 2K and sanded lightly. I was spraying an acrylic enamel of 8 parts color, 1 part hardener, 2 part reducer as called for on spec sheet. I was using a regular (not HVLP gun) touch up gun at about 40-45 lbs. pressure. As I was going over it with a second coat, I noticed scores of tiny air bubbles forming on the surface of the panel. I continued spraying since this was only a test for color, but when the panel dried, the bubbles of course remained in the finish.

Thank goodness this was only a color test and not on something I was finish spraying. I've done some painting before but not had this happen. What was the cause? Too much pressure? Poorly mixed paint? Defective gun?

When I do decide on a color, I will spray with a new HVLP gun that will have a digital regulator attached at the handle of the gun.

Obviously I want to avoid such a disaster later. Your help and advice are greatly appreciated.

Yours,

Jim

Got any pics of what that looked like?

The bubbles are caused by underlying vapors outgasing. How long did you wait before applying your second coat? I'll let someone more familiar with modern materials be more specific but I doubt that it was caused by your gun or the pressure used.

I thought the HVLP guns were supposed to run at 20 - 25 psi? That is what is called for on both my large and small touch up guns. Not sure if that would cause your problem, but it is the first thing that popped into my head.

He said he wasn't using an HVLP gun.

Tiny posted the most likely answer. Something is degassing.

How long did you wait before applying your second coat?

What are all the things you put under the acrylic enamel?

How long ago did you put each of these layers/materials on?

Were all layers of underlying material from the same manufacturer (and listed as being compatible)?

Tim

Sorry, missed the "not" part.

Here are a couple of guesses... Of course I have not sprayed acrylic enamel in 15 years or so.. Spraying paint in direct sunlight or on a surface that is too warm can cause acrylic enamel to blister. Like cold paint on a hot surface. Spraying on a damp surface can cause it too. Excess humidity.... I have heard of folks using lacquer thinner on their tack rags and that can cause it, usually that is a streak.. The paint will fry of sorts.
If the first coat went down smooth and then blistered on the second coat you may not have let the first coat flash off enough. As the thinner evaporated it caused the bubbles... maybe...

I don't know if that helps or not.. I guess it is just an opinions.

I applied 2K primer to bare clean metal about 2 days before spraying the color. I sanded the primer with 600 grit, then cleaned, then sprayed the color coats. The 2K and color coats were not from the same manufacturer.

I was NOT using an HVLP gun.

I probably did not wait long enough to apply the second coat--I didn't time it but it was probably within 5-10 minutes. I suppose I should have let it set more like 15-20 minutes? Was that the problem?

Thanks again for your help.

Jim

Michael,

Thanks for your ideas. I was spraying in the sunlight, though it wasn't a particularly hot or humid day. The surface wasn't really "blistered"; these were tiny bubbles, which when dried, feel almost like sand particles here and there on the surface.

Thanks,

Jim

Sounds like solvent pops. Try waiting longer between coats. What's happening is the solvents that are evaporating from the first coat are getting trapped under the second coat. Wait til you can touch it, then put the second coat on.

I think you may have found your problem. If the paint skims over before the volatiles underneath have escaped you can get out-gassing. Try shooting a test sample in the shade.

If the sun was on the paint job, I think that could cause the surface of the paint to try before gas could escape. Paint will want to dry outside in usually it is not a problem unless the outside dries much faster than the inside.

Of course that is just another guess on my part.

I'm with tiny, I've recoated at 5-10 min. with no problems. but that sun will skim the paint over on top and the thinner has to get out somewhere

Guys,

Thanks--it makes sense. I'll try shade and some more time betweeen coats next time.

I appreciate your help.

Jim