Many metal roofs are made out of galvanised metal, which is a type of metal that has been covered with hot zinc in order to protect it from the weather. However, paint on metal roofs often peels or rusts, in which case it is time to repaint it.
Use your putty knife or scraper to scrape off any peeling paint or accumulated rust on your metal roof. Get off as much paint or rust as you can. When you are finished scraping, use a power washer and wash the rest of the debris off. You want to have a clean and paint-free roof when you are done.
Mix 1 cup of chlorinated bleach with 4 cups of warm water and 1 cup of trisodium phosphate (a cleaning agent). Use your sponge or paint roller to apply this solution to your metal roof. This will get rid of any mildew or algae. Wait until the solution dries, then rinse it off the roof with water.
Apply the galvanised metal primer to your roof with the paint roller. Wait until the primer dries completely before you begin painting.
Consider different top-coat paints depending on the climate. If you live in a moist or wet climate, aliphatic urethane coatings work best. However, if you live in a dry and hot climate, acrylic urethane is the best choice.
Use your paint roller to apply acrylic top-coat paint. Apply two coats in total, letting the paint dry between coats.
Less-toxic acrylic primers usually are recommended for galvanised metal roofs; however, solvent-based primers are just as effective if you choose to use them.
If you are working with solvent-based paints or primers, always wear protective eyewear and gloves to prevent direct contact with the toxic solution.