Galvanized metal roofs are coated with a layer of zinc that inhibits rust. Unfortunately, over time, this coating can fail, leading to minor rust outbreaks. If you are preparing to paint a rusted galvanized metal roof, pay special attention to surface preparation or you will have a recurrence of rust and/or flaking. Paint will not adhere to your metal roofing unless you apply an etching primer first. Once you've conditioned the galvanized metal to accept paint, apply a rust inhibitive primer to prevent a recurrence.
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Access the rusted galvanized metal roof, using an extension ladder. Scrape rust from the roof, using a wire brush.
Wash the galvanized metal, using a pressure washer. Wait a full 24 hours for the roof to dry.
Fill a plastic 5-gallon bucket with two gallons of galvanized metal etching primer. Affix the shed-free cover to the roller frame and attach an extension pole.
Carry the plastic bucket up the ladder and set it on the roof. Descend the extension ladder to collect the roller and paintbrush.
Apply the metal etching primer to the rusted galvanized metal roof, using the roller. Begin at the far side of the roof. Roll in a vertical motion, working backward toward the extension ladder. Wait three hours for the metal to dry. Touch-up areas, inaccessible to the roller, using the 3- or 4-inch nylon paintbrush. Wait four hours for the primer to dry.
Clean each painting tool with water.
Apply a water-based rust inhibitive primer to the roof in the same manner as you did the etching primer. Wait two hours for this particular primer to dry before adding a coat of acrylic latex paint to the primed roof.