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by Ron Joseph

February, 2005

Paint Blisters, (Pimples) in Automotive Refinishing Job

Q. I just had my 74 Chevy Nova completely restored about a month ago. They took it all the way to bare metal, cut out the rusted lower quarter panels, sanded, primed, painted, clear-coated and rubbed it out.

I was thrilled with the job until this week when small "pimples" showed up in the finish of the hood, tops of the front fenders and, to a lesser extent, the roof of the car. The pimples are typically about 1.5 mm in diameter and stand proud off the surface about .03 mm.

I'll take it back to the shop, of course, but I'd like to have a bit of an idea about what might have caused this.

Thanks for your input.

A. This sounds to me to be typical of what we call "solvent entrapment". It is possible that there was a lot of solvent in the paint during the painting operation. If the paint skinned over too fast, then the entrapped solvent could not get out fast enough. Hence the blisters (pimples). You pointed out that the blisters were predominantly on the horizontal surfaces. This is an indication that more paint was applied to the horizontal surfaces than to the vertical surfaces (doors, etc.) If more paint was applied, then more solvent was entrapped. This is a paint application problem and the body shop should repaint your car. BUT, if they agree to do so please point out that they must allow sufficient time for the solvent to evaporate before apply the next coat of paint. Also, they should be careful to monitor the film thickness on the horizontal surfaces.

Please get back to me after the car has been repainted and let me know the outcome.

Best wishes,

Ron Joseph

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