If a product has been sprayed with a first coat of galvanizing paint,
is there a special primer that can be a 2nd coat over the galvanizing
that will enable a 3rd coat of paint chosen because it holds up good against sunlight?
What primers do automakers use that will enable paint to stick to zinc coated sheet metal?
Gulf of Mexico off-shore platforms are commonly sandblasted to white metal, primed with zinc-rich primer, primed again with regular primer, and then top coated with paint. You can mimic this marine paint system with good cleaning, zinc-rich primer, followed by regular primer, then top coated. Several times I have used any good rattle can primer over zinc-rich primer and then top coated with good result.
Auto makers use paintable zinc coated steel sheet called Galvanneal, which is cold rolled steel sheet that has been hot dip galvanized or electro-zinc plated followed by annealing. The annealing process causes iron atoms in the base metal to mix with the zinc atoms on the surface, making the surface paintable. So galvanized steel sheet is not paintable, but heat treated galvanized sheet is paintable. Galvanneal is also the non-rusting metal most often used in painted and un-painted electronic and computer cabinets/frames, and it is often automotive gauge, 0.032", because that is a common and economical thickness with high availability in the steel market.
