Imperial Home Page -> Repair ->Body -> Paint -> Blistering
Question from Bill:
We store our "classics" under covers and in a car port over Winter. Yesterday I went out to check on them and when I pulled the cover off one of them I find a large percentage of the car's paint has what looks like widely disbursed "goosebumps", not pointed but domed like water beads. I pressed down on a few with my finger nail, but they do not compress or break.
Any paint gurus out there have a clue what this could be?
Replies:
From Ken:
The thing your experiencing is BLISTERING. It's caused by trapped solvents or (worse case scenario), body filler. When body filler expands and contracts (when its thick) it causes this. Or the same with bad preparation, either way, its not good!
From Kerry:
If it has been several YEARS, I hate to think that it is out-gassing NOW. I'd tend to suspect there was surface rust under the repaint that was NOT killed. It took some time to grow to the point where it lifted the paint.
What makes me say this is your comment that the bumps are HARD. I had an out-gassing problem several years back. It showed up within a month and the bumps were 'soft'. I could press a thumbnail in them and see the mark.
If you have a bump in a spot that is not easily noticeable, you might take a sharp knife and pick it open and just see what's inside. Either way it's not good.
I had used some polyester finishing putty over some minor pits, sanded, primed with urethane, and laid the color. All in a couple days. EVERY where I had used the putty developed blisters.
The bad news is that there is NO CURE except taking off the paint down to the problem and redoing the panel.
Modern paints are impermeable. Old style lacquer primer will outgas for 30 days. New Urethane primers are done in an hour ( I still like to wait a few days before sanding though. It just seems to sand better).
I don't know how production shops can do things so fast. Well actually I do, they have ovens that bake things to speed up the process. I guess that works for fillers also.
From Luke:
Have been painting cars myself for over 15 yrs, and have many friends in the auto repair and bodywork businesses. Cant actually picture what you are describing and have seen a lot of messed up paint jobs from all sorts of issues. Normally either it wasn't prepped correctly, filler is too thick, rust underneath is coming through, paint additives chosen incorrectly, etc... but you make it sound like it is all over the car.
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