powder coating can be applied over zinc type primers.  see the following
web page for primer and corrosion resistance specifications for powder
coatings.
http://www.pfonline.com/articles/clinics/1202cl_pwd5.html

good primer selection will most certainly aid the longevity of any coating
be it paint or powder coat, as will good preparation and attention to
detail.  although i have gotten the impression that when most people do
powder coating they do it themselves or send it down the line at the local
low cost shop.  in these type cases i think that if you live in the
rustbelt and subject your parts to salt spray you would be better off with
paint that by its self has a good creep resistance.

jonathan

On Wed, 29 Oct 2003, Doktor Tim wrote:

> At 07:42 AM 10/29/2003, you wrote:
>
> >the down side to powder coating in my rustbelt experience is the lack of
> >creep resistance.  although you can purchase creep resistant powder
> >coating supplies almost no one that i know of uses them.  take a look at
> >trailer hitches to see what i mean.  the powder coat comes off in sheets
> >after the rust creeps underneath and the pressure exerted between the
> >steel and the powder coat peels the powder coating off.
>
> I expect this can be prevented by a better preparation process. It's just
> like chrome. If it's done quick and dirty to meet a price point it will
> fail. If extra time/money is invested in good application, preparation and
> process, it can refuse such issues and give long life. I've seen lots of
> production chrome fall off in sheets the first time you flex it. I've see
> good chrome you can't get off without grinding or acid. You can only remove
> it molecule by molecule. I don't know, can powder coat be applied over 98%
> zinc primer?? That's the way to stop rust creep for enamel. Thorsen process
> zinc coat would surely add both to cost and longevity in regard to any
> scratch that might get through such a high load part as a trailer hitch.
>
>