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How to Clean White Rust on a Metal Roof

Brad Chacos

Galvanized metal is a popular roofing material due to its low maintenance and upkeep requirements, relatively easy installation and long life. A thin layer of zinc applied to the surface of the metal protects it from rust and corrosion. Unfortunately, the zinc itself can corrode if it comes into extended contact with certain materials such as steel debris, cedar or dirt and grime. Zinc corrosion appears as a white stain and is known as white rust. Clean white rust from a metal roof quickly to avoid the zinc corroding completely and leaving the metal underneath exposed to the elements.

White rust can lead to roof holes if left untreated.
  1. Remove any items that could be causing the corrosion, such as copper pipes or items made of lead.

  2. Pour white vinegar over any areas affected by white rust. Allow to sit for five minutes, then rinse and wash the area with warm water. If the stain is removed, apply a coat of zinc-rich, water or solvent-based rust resistant primer over the area and do not continue with the rest of this process.

  3. Scrub any remaining white rust with sandpaper until all signs of rust are removed. Repeat for all affected patches of roof.

  4. Thoroughly rinse the sanded areas with warm water, then dry all moisture with a clean rag.

  5. Apply a coat of zinc-rich primer to the sanded areas. Allow to dry, then coat the entire roof with galvanized iron primer, being careful to avoid stepping on any primed surface. Allow to dry.

  6. Finish the roof by applying a layer of outdoor-use paint. Apply extra coats as necessary to obtain an even look to the shading of the paint. Allow one coat of paint to finish drying completely before applying another coat.