Alkyd zinc primer ?

[torredcuda]

I can get some Sherwn Williams Alkyd zinc primer free from work and need to know if I can top coat an epoxy type primer over it.It it a marine /industrial type TT-P-645B.Anyone use this stuff or something similar?I have the MSDS but it says nothing for topcaoting.

[dutch]

I would try to find out how that stuff behaves when sanding.  If hard to sand I`d stick to epoxy only. ( which doesn`t sand very well either... )
Take some sheetmetal and do some tests 

[torredcuda]

The zinc primer is sorta like an etch primer in that it is just for adhesion and and corrosion protection,I would immediately shoot an epoxy primer over it.

[gomangoRT/SE]

industrial and marine zinc coatings are called "sacrificial" coatings.  Used for bare metal immersion type systems.  It adheres well and is used only for that purpose.  Your intermediate coat (in this case epoxy or whatever you use) should be used within the time frame listed for the product.