On Thu, 1 Sep 1994, POCHE@music.loyno.edu wrote:
> I need some more NET wisdom please!
>
> I've been going around fixing little dents and dings in preparation
> for a real paint job in the near future.
>
> What I am trying to do is sand down enought to remove any rust,
> repair the whole/dent/whatever. Then spray on primer and
> paint to seal up the repair while I'm waiting for the paint job.
>
> WELL, I might as well be spraying on paint remover.
> The top layer of old paint just bubbles up and peals away.
>
> THis is happening at the top coating of paint.
> The TOP color layer is the one peeling off.
>
> WHAT AM I DOING WRONG!!!!
>
> Is it the cheap canned spray primer (I've tried several differnt
Actually, Louis, if you are using any filler in your dent repairs, you may
be wasting your time. A bare metal respray is probably needed to avoid
problems with the paint layers already on the car. Whether you bring it
to bare metal with paint remover or by sanding, you are going to mess up
the filler you have just applied, and have to do it over. Plastic filler
is porous. Paint remover will soften it, and possibly get in the pores.
Sanding will erode the filler unless you are supremely careful to quit the
instant the paint is gone. You would be far better off to do it all at
once. But if you want to continue, read on.
In a word, yes, it is the primer you are using reacting with the top paint
coat. My guess is that the top coat of paint is either cheap alkyd enamel
or acrylic enamel applied without hardener, and your primer is lacquer.
Lacquer thinner will lift enamel unless the enamel is *very* well cured,
and sometimes even then.
Check your primer can; it almost certainly will say it is lacquer or
"lacquer type." If all you want is a holding action until you do a proper
repaint, I suggest the following:
Try applying your primer in several very thin coats, with an hour or more
between each. That may avoid most of the problem. Do the same with your
color coats, if you are using lacquer type color as well. Or try omitting
the primer; I am not convinced that lacquer type primer does much except
fill roughness, anyway. This may not avoid the problem, however, if the
color coat is lacquer, for lacquer type color coats may lift the old
paint; it is the carrier that is the problem, not the pigment.
If these suggestions don't work, then your only real solution is to use
enamel over enamel. If you must use spray cans, use the closest match you
can find in rustoleum or another good brand of household enamel. If you
want to prime your spots, use a primer they recommend such as damp-proof
red. Don't use rustoleum "auto type" primer; I think it is lacquer.
Follow the instructions to the letter. In particular, if you are going to
apply more than one coat of rustoleum, either do so within an hour or wait
48 hours. The second coat of rustoleum can lift the first coat if you
disobey.
But beware. When your car is painted, you should remove all traces of
these temporary paints and the troublesome paint that is lifting now.
Your problems illustrate why it is best to do a bare metal repaint with
epoxy primer. Modern paint systems have made it possible for paint to
fail in more ways than ever before.
Ray Gibbons Dept. of Molecular Physiology & Biophysics
Univ. of Vermont College of Medicine, Burlington, VT
gibbons@northpole.med.uvm.edu (802) 656-8910
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