Adriatic posted:JHZ, You want "etching primer" for the galvanized (automotive supply or painter's supply house), cost is higher; but great stuff. (kinda hard, so hard to sand too. Go light and easy; no runs, etc.) Everything else will eventually chip or peel. Etching primer chemically treats and binds to the zinc (or other hard to paint metal too like brass, copper, etc.) You either didn't clean with a solvent, didn't allow full cure, or didn't use compatible paints. (unusual for a topcoat to react to a primer... is that the case?... If so, brands type& color please....so we don't repeat it)
I use the Rustoleum etching primer and I usually prep the surface on all my tin (after stripping if necessary) wit scotch brite and lacquer thinner. Make sure you test your top coat on a separate piece with the final color paint to make sure there is no reaction to the two paints
