Thread: Primer problems

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Today, I was spraying Sherwin Williams 21 catalyzed polyester primer thinned with 1 oz acetone per pint. (SW recommends thinning up to 2 oz per pint to extend pot life) I use a DeVilbiss Finishline HVLP gun with a 1.8 tip. The gun is clean. The temperature was about 72 F, and very low humidity. It turned out like crap. Coverage wasn't good, the surface is somewhat orange peeled, and didn't flow out.

I don't have a pressure gauge at the cap, so I varied the input at the gun from about 10 psi up to about 20 psi. Didn't seem to help.

When I had trouble like this before, it was due to feeding too much paint, or the paint was too thick. It took a quart to spray my '34 hood, trunklid (inside and out) and one door. I should get about 200 sq. ft. from a quart, and there can't be more than 50 sq. ft. in those three parts. However, if I turned the fluid control in much farther than I had it, the spray would get really misty, and it started to look like a dust coat.

This primer is supposed to spray right out of the can, but I'm starting to think that it's too thick.

Another clue I noticed is that I had a difficult time getting a nice wide fan. With only thinner, I got a nice 8-9" fan. With the primer, it narrowed down to 6" or less. Sounds like another hint that the paint is too thick.

I sprayed the body a couple of weeks ago with Transtar 6541, which is virtually identical. I got pretty good coverage, with only a slight orange peel. I attributed that problem to the cool weather, since it was 60 F or a little less.

Any comments or helpful hints from you paint wizards?