The first thing you must do is clean the entire surface. Although many people skip this step it is required when painting metal because any rust or filth will compromise the durability of your paint job. Over time metal can become greasy, it can contain dust or moisture and all of these things can stop paint from adhering to the surface.
In order for paint and primer to adhere to the surface you will need to make the surface rough which will require steel wool, sandpaper or a wire brush to score the surface. This process will insure that the metal is rough enough for the primer to stick to the metal ad it will also remove any loose rust.
Once the metal is clean you will want to find a primer that works on metal. A good choice is a zinc chromate primer because it is corrosion resistant. This will help retard any rust that might want to come back to your metal. Many experts suggest that painting the primer on with a brush to work it into the surface more is better than using a spray paint.
Once the primer dries you can apply several coats of the paint color that you chose for your metal. It is very important to let each coat dry however before going onto the next. If you become impatient between coats and try to move it forward too soon, you will find wrinkling, cracking or bubbling within your paint finish.
Whatever product you decide to use must have some kind of rust inhibitor to stop the future problems that your project may encounter.
Rusting metal doesn’t have to be a problem if you know what to do. If you have a large surface you may want to ask a professional painter to help you.