How to prep bare metal for painting - confused and need help

[Michael Craig]

So I'd like to tidy up the worst of the cracks, blisters and blemishes on my 88", and then do a new top coat over the whole truck. There's quite a bit of bare aluminium that evidently has been sanded down with 3/4" gravel, and not 150 grit garnet; so the brite finish has been badly compromised.
I've read lots about Zinc Chromate treatments; Phosphate and Chromate conversion coatings; phosphoric acid wash primer etc etc etc; and am more confused than when I started.
Can anyone help by relating their personal experiences with re-finishing from bare (and very rough!) metal?
Thanks

[gudjeon]

Zinc Chromate primer on bare aluminum. Get the good green stuff. It is a bit transparent so you spray it until it just obscures so it covers up a newspaper printing - as a guide to how thick. Then spray with auto primer and prepare like normal.

[Michael Craig]

Thanks for the info Jon. Can I just sand the aluminum; apply the ZC primer; then primer and topcoat? Or do I need additional prep before the ZC application?

[gudjeon]

I sanded the ally and put on the the ZC right away. I used the plastikote industrial stuff in spray bomb from Napa. I put the ZC over everything, bare ally and sound paint underneath. It makes subsequent primer stick to whatever its on. Use a good filter mask and very good ventilation. It can rearrange DNA.