White Rust

White rust is often referred to as a condition in which a layer of zinc oxide (ZnO) is forming on the surface of a galvanized product. The appearance of white rust is different then red rust: As the name implies, zinc oxide has a shade of white and can have occasional light brown spots. White rust looks like white powder being attached to the surface of the product. 

As soon as the product has been galvanized, a zinc oxide film begins to form on the glossy zinc surface, which is usually not visible to the naked eye due to the film being so thin to allow light to pass through.

It is possible to see when such galvanized product is used in open air without a second protective coating. A dense zinc oxide film will form on the galvanized surface and the gloss is gradually lost. White rust is the most common problem associated with galvanized steel products.