Galvanized metal roofs, once scratched, are liable to rust. Other damage that removes the layer of zinc that prevents rusting can also cause rust that will degrade the metal over time. Once you spot rust, the best course of action is to remove the rust and paint your galvanized metal roof. By choosing the correct primer and paint, you can inhibit rust for at least 5 years before the roof should be repainted.
Step 1: Remove any visible rust, first using a wire brush, and then using sandpaper to remove any remaining rust residue.
Step 2: Wash the surface of the roof with a pressure washer using a low pressure tip to prevent damage. A scrub brush with soft bristles can remove any stubborn dirt from the surface of the roof.
Step 3: Apply primer to the surface of the roof using a long napped paint roller. When picking a primer, be sure to choose one suitable for use on galvanized metal roofing. A metal etching primer is the best choice, and should prevent the paint from flaking over time.
TIP: You won’t be able to cover all areas using a paint roller, so keep a paint brush with you to touch up small spots and paint around obstacles around the roof.
Step 4: Allow the metal etching primer to dry 8 hours, or as long as recommended by the manufacturer.
Step 5: Apply a coat of rust inhibiting metal primer over the metal etching primer. The use of two, separate types of primer will reduce the chance of both flaking and rust over time.
TIP: It is very important that you achieve even, thorough coverage over all of the galvanized roofing to prevent rust. For this reason, take some time with your paintbrush and the rust inhibiting primer to retouch any sections you suspect you may have missed.
Step 6: Allow the primer to dry for 8 hours, or as long as recommended by the manufacturer.
Step 7: Apply a coat of acrylic latex paint onto the surface of the roof. Let it dry completely, then apply a second and final coat.