On Mon, 11 Nov 1996, Robert J Donahue wrote:
> <primer) it is water resistant. If you get it rained one before you get
> the
> <finish coats on, it doesn't absorb water. Many people (especially kids)
> who
> <have to drive a car with some primer exposed before it's all done, have
> What? I thought primer was supposed to be wet-sanded before applying the
> top coat. At least that is what I've been doing. I'm using Rust-Oleum
> automotive primer. It says on the can that it is wet-sandable. Does this
> advise apply only to certain primers, or am I in trouble?
I'd say the problem isn't so much that ordinary lacquer type primer surfacer
absorbs water, but it is little protection against water. If you spray
lacquer type primer over bare metal, then wet sand it, there is a chance
rust will start under the primer because it does not really seal the
surface. The finish you apply may fail, not so much because you trapped
water, but because you allowed rust to get a foothold. I suspect it's a
lot worse problem for prolonged weather exposure than for brief periods
of wet sanding. Hot rodders used to coat their cars with primer, then
drive for a year or two (I think I went 18 months) until they could
afford paint. After that much time, you were certainly taking a chance.
Although that may comfort you some, I'd also say that lacquer type primer
surfacer (which I believe the rustoleum light grey auto type primer is) is
nowhere near state of the art for adhesion to bare metal. Over the last
30 years, I've experienced a lot of peeling of paint when this was used as
primer over bare metal. The new epoxy and etching primers are *far*
better at both adhesion and water protection.
If you coat the bare metal with a good modern primer, you can then coat
that with primer surfacer and wet or dry sand it as you want. I prefer
dry sanding, at least until I have a good dependable paint film built
up. There's nothing quite so annoying as starting to spray your final
finish and having a little track of water blow out of a fender seam.
Your gumption just evaporates.
I'm concerned you may do a lot of work and have an early paint failure
that will bring it all to nothing. At least check Eastwood; I believe
they sell etch primer in spray cans.
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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