Zinc-clad primer?

Sherwin-Williams store sells spray paints, one of which is called "Zinc-Clad Cold Galvanize Primer".
What is this for? When would one want to choose this over the "regular" primer?
Is this an "etching" primer? Is it always better to choose this over others?
Thanks.

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No, it is not an etching primer. It is zinc powder with just enough binder to make it stick. It is used to touch up galvanized metal where you have welded to it or ground the zinc off.
Paul K. Dickman

Also when you build something out of pipe - the wrenches eat up metal and it will rust.
I build a weather station from pipe and before I put it into concrete or mounted anything on it, I sprayed it down with cold-zinc and then over painted the entire pole with black. The paint over the zinc prevents zinc migration or 'melting' that leads to rust.
Martin
Paul K. Dickman wrote:
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On 9/6/2009 1:58 PM, Paul K. Dickman wrote:
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I used it on the surface of my monster vice and then over painted that.
As I was told, take a galvanized pipe - paint it and the pipe will last many many more years. Galvanize over it with cold (sealer) and paint or not - and you extend it longer.
Martin

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I used it on the frame of my homemade trailer. It does not seem to rust, except where it was scratched off, and even there the rust does not "get under" the cold galvanizing.
i