I've been following a bit of the primer debates, and will offer some of
my experiences (for what it's worth).
1. 59 pickup, stripped off paint in August 1980, etched with metal
prep, sprayed on lacquer primer in Sept 80, painted with acrylic enamel
in May 1981. Drove it the whole time. Paint is still just fine (no
rust), but getting thin where it wasn't put on thick enough (primer
showing thru, no rust) and lots of chips over the years. This truck has
spent a lot of time outside, but also about 10 years in the garage.
2. Other 59 pickup, sanded down repaints to get to original paint, did
bodywork in places, primed with lacquer primer, and painted with Dupont
Prime-n-Seal (tinted with color) in 1994. The primer has faded badly,
gone away in places, rust showing thru in places, and it's looking
pretty shabby. This truck has been parked outside most of the time.
3. 55 Belair, sandblasted, sanded, metal prep, primed with Dupont Uro
primer, did more bodywork and sanded and primed a couple more times,
last coat was tinted Uro primer in 1997. No fading anywhere, no rust,
I think people don't realize that if water can get into porous lacquer
primer, it can also get back out again...park the truck in the sun on a
warm dry day (most days here in Arizona), and it will not have any
moisture in it. Or, park it in a heated dry garage for a couple days,
and there won't be any moisture in the primer.
I don't know if you need to phosphate or zinc treat or galvanize steel
under the paint...but I know that a good two part primer (such as Uro or
the PPG equivalent) will hold up well, adhere well, and sand well. When
I did the 55 I omitted the self etching primer that is supposed to go
between the metal and the Uro (I forget the name, but it's green, and is
supposed to go on thin, and promote adhesion). The Uro sticks just fine
without it, thanks.
If you're carefull with bodywork and metal preparation, and don't lay
the paint on too thick, you shouldn't have any trouble. No need to get
too excited about using exactly the right "stuff". Just have fun doing
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