If you are planning to paint a corrugated metal roof, you should understand some key points. Metallic roofs are hard and nonporous, making them ill-suited for paint adhesion. You must abrade the roof with a special type of acidic primer, prior to painting, or the finish will flake. In addition, because corrugated roofs are prone to heavy runs and drips, you should employ a particular application method that will promote a smooth, professional-looking finish.
Access the corrugated metal roof using an extension ladder.
Clean the exterior metal roof, using a pressure washer equipped with a low-pressure tip. Wait 2 to 4 hours for the roof to dry.
Cover portions of the corrugated metal roof you do not want painted with professional painter's tape. Cover the areas beneath the roof with heavy-duty fabric dust sheets.
Coat the corrugated metal roof with galvanised metal etching primer, using a roller with a nap cover. Roll only a 3-foot-by-3-foot area at a time. Smooth the wet primer, using a paintbrush, manufactured for use with water-based coatings. Continue until the entire roof is primed. Wait 2 hours for the primed roof to dry.
Wash the roller and brush with water.
Coat the primed corrugated metal roof with acrylic latex paint. Apply the paint just as you did the etching primer. Wait 2 hours for the primed roof to dry.
Never paint a bare corrugated metal roof or the paint will peel. Do not use an ordinary acrylic latex or oil-based primer on a metal roof or the finish will fail. If you are inexperienced with extension ladders, read the safety instructions on the side of the ladder before you climb it.