How to Paint Galvanized Sheet Metal, Gutters, or Valley Tin
By: Danny Lipford
How do I go about priming and painting galvanized valleys and flashing on my roof? -Abbey
If galvanized metal is not prepared and painted properly, it will tend to peel over time. Clean new galvanized metal surfaces with a water based cleaner/degreaser to remove any oil or and contaminants. Once the metal has dried, dampen a cloth with white vinegar and wipe the surface down. The acid in the vinegar will act to etch the metal and help the paint adhere.
On older galvanized metal surfaces where the zinc coating has begun breaking down (known as white rust), use a wire brush or fine sandpaper to remove the chalky film before cleaning it.
Once the metal has been cleaned and is dry, prime it using an exterior multipurpose latex primer, or a latex primer that is made specifically for galvanized metal. Topcoat with two coars of a high quality exterior latex paint.
Good luck with your project,