Originally Posted by Jolly Roger bus 223
a plain old white vinegar wipe down will take the coating down enough for the paint to adhere on galvanized areas especially new metal that you want to prep for paint.
still need an ospho or something of that nature for the rusty areas
That's what we did for many years in construction, etch with plain old white vinegar brushed/wiped on, dried, wipe off and paint. Seemed to work, but I never really checked the jobs years later to see the results.
But we usually painted with latex or oil based paints. I stayed out of this, until now, because I don't have experience with the new paints. On steel, my understanding is that phosphoric acid converts the rust to iron phosphate, maybe it just etches galvanized like vinegar. Most brand name phosphoric acid products also claim to have additives to make them superior (and charge more $$). Who knows? Not me.