Are there any cold galvanizing compounds that can be painted over? I
have some areas on my car where the paint is lifting but where water
normally gets trapped (under weatherstripping), so I'd like to do more
than just paint over it the usual way. Is it OK to simply use
phosphoric acid metal etch or etching primer over cold galvanizing
paint, or will this cause it to lift?
I've used Centari acrylic over ZRC cold galvanizing paint with no problems
on my frame rails. You can't use alkyd paints over zinc rich coatings. On
sheetmetal, treatment with phosphoric acid followed by a primer and topcoat
should be sufficient.
These are usually labeled zinc rich primer, meaning to me they are meant to
be painted over. I did a job for the dept. of transportation several years
ago that specified galvinized pipe, with all welds sprayed with zinc rich
primer, followed by 3 coats of paint. I had them painted by an outside
source so I can't tell you particulars, but I can tell you it can be done.
The problem is that all spray zinc primers I've found in the stores
and a half-used can that was obtained from an industrial supply house
had warnings against being painted over. I just haven't had luck
finding anything that says it can be painted over, and since with
zinc-plated metal supposedly needs special primer, I though that the
same would be true of anything coated with cold galvanizing paint
since it's 95% zinc powder.
Try Clearco Products, I have bought hundreds of cans from them, they are
good to do business with and they have zinc rich spray thats made to be
painted over. I know this stuff is routinely painted over in high corrosion
enviroments, the DOT stuff we built was underwater part of the time.
On 6 Sep 2003 00:00:23 -0700, email@example.com
I have no idea,
Indeed. You can't use any kind of normal pain for that, because
regular paints aren't waterproof. All will allow a few water molecules
through, and that's enough to cause rust.
There is however a rather expensive plastic 'paint' that is absolutely
waterproof and which will stop rust dead in its tracks. It has no
problems with being painted over. After two salt- laden Canadian
winters my winter 'beater' still shows no sign of rusting where I've
applied that stuff.
An unsolicited testimonial from a satisfied customer.
I don't know about "no problems being painted over." If you let POR-15
harden, you have to *really* scuff it up to get paint to adhere to ir.
It is, however, uneqivocally Good Stuff. Only gotchas about applying
it: 1) it WILL NOT adhere to grease, so while surface rust is just fine
and dandy, you usually end up using some powerful degreasers if you want
the stuff to stick (I usually use it on frames etc. and underneath the
engine requires lots of prep work) 2) if you get any on you, wipe it off
right away with lacquer thinner because if it dries on you, it's there
until your top layer of skin is ready to be scrubbed off.
Oh, and if you're using it in a non-underside-of-car application, you
will want to topcoat it because the color fades in sunlight.
It has an optimum paint-over 'window' about 3 hours after it is
applied. After that you need to rough it up. The problem is that it
doesn't dry, it hardens the same way silicone adhesive does, from
exposure to atmospheric moisture. Local humidity affects drying time.
Do you know anything that does?
My one lament is that they don't make the stuff in clear anymore.
At least that didn't show so bad on your skin.
It gets sort of dull and weatherbeaten looking. But in that condition
it takes a topcoat really well!
Bonus: you can use it with fibreglass instead of the usual epoxy resin
to make patches. Unlike such patches that use epoxy, POR15 ones won't
rust out underneath their bonding surface.
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