Best primer & pain for old galvanized
My workshop roof is old heavy gage galvanized. It's probably at least 40 years old, but in very good shape.
It has a coating of what looks like aluminum paint, which has flaked off in various areas. In some areas there is surface rust.
Naturally I'd like to stop the rust and/or prime and paint the weathered areas.
I coated about half of the weathered areas with Rustoleum Red Primer, before I (re)-read the label that says it's not for galvanized. But I'm guessing that since it's rusty/weathered/old painted galv it might be ok.
For the rest I'm looking for a better solution. So far I have found:
1) Rustoleum white latex primer for aluminum and galvanized
2) "Rust Converter" primer (kind of brownish) which says it's ok for galvanized.
3) Rustoleum clean metal primer (white).
4) Rustoleum cold galvanizing spray.
5) More Rustoleum Red Primer
So... I'm a bit unsure which to use. I really don't like the idea of using a latex primer on a roof, especially since it will be covering surface rust and be topcoated with an oil-based enamel. The Rust Converter primer is a bit pricey - but it comes with a five year guarantee. I have not been impressed with cold galvanizing paint in the past. I have noticed it tends to be very weak, easily scratched off clean metal with a fingernail, even after a long drying time. But the Rustoleum version has less zinc in it (93%) than the kind I used before (99%) so maybe it has more resins to keep the stuff in place.
For topcoating, I'm looking at Rustoleum Industrial Hi Performance Aluminum oil-based enamel. I do have some doubts about top coating galvanized surfaces with an aluminum paint, however, since the zinc in the galvanized probably will try to sacrifice itself to protect the aluminum - or so I gather from the tables.
What seems to me to be ideal for this would be a zinc-containing primer, and a zinc containing silver-colored top coat. But I haven't been able to find those items as yet.