How can I paint galvanized metal?

Question

I often have metal gates galvanized and are required to give the final product a coat of paint.

As is known about galvanized metal, the zinc begins to oxidize with the air and creates the flaky powder which repulses the paint thereby flaking off the paint.

I have been told many things about galvanizing and how to paint / prepare for painting and was wondering if there is a generally accepted best practice here. What i have heard is the following:

• you need to wait at least a month to get the galvanized layer to oxidise, then paint
• you need to prepare the surface with a mild acid to remove oils (either vinegar or galvanized metal cleaner)
• do not use oil based paints (either primer or paints) since the oil does not adhere to the coating
• paint first with an etch primer which will etch and bond to the surface, then paint
• forget primers and just apply two coats of acrylic paint which bonds well to the surface.

I guess, as with any paint application surface preparation is key, just interested to know what the professionals do here.

Answer 1

This is an answer from yesterday in another question thread:

Priming and Painting Galvanized Metal, condensed from KILZ.com, other manufacturers also make specific paints and primers for galvanized metal.

The galvanizing process, which is designed to prevent rust, leaves an oily film that can prevent coating adhesion. The zinc in galvanized metal can produce a milky “white rust” (which is common when it has weathered) that must be removed with a stiff brush or abrasive pad, prior to coating. It’s necessary to remove the oily film that can prevent coating adhesion with a water-based cleaner/degreaser.

Prime the surface with a water-based primer. Since oil-based primers can interact with the zinc in galvanized metal, causing premature peeling, always use a water-based primer when painting galvanized metal. KILZ® 2 Primer is an excellent choice when priming and painting exterior galvanized metal. It will grip to the metal surface and provide a better surface for the paint to adhere.

todayshomeowner.com/how-to-paint-a-galvanized-metal-door

Answer 2

I've seen a product used that turned the zinc galvanising black, but can't remember what it was called (will update if I remember).

Other than that, etch primer - with a thorough degreasing beforehand.

Another option to consider would be having the gates powder coated rather than painting them.