That is very true. I have mentioned using Ospho to clean metal, and that it can react to any primer that also is acid based. I had a hood once, it had lots of surface rust/pitting. I DA -ed it, used a big wire cup on the right angle grinder on it, LOTS of pitting! I put a good coat of Ospho ( phosphoric acid sol), let it dry over nite next after noon I used a foam brush to apply heavy coat of Rusteolum enamel, just to what would happen. I wrinkled it places, After it was totally dry, and couple months later, tried to da it off, I could not dent it!!! Had no shine but...... the acid reacted no doubt with the enamel. It was still adhering well 2 yr later, and still DULL! but it was not rusting.
Epoxy primer is great stuff, on clean bare metal and as a sealer, I think.
