What is it?
This is primarily a galvanize defect. It appears as a white, chalky, stain-like appearance on a galvanized surface. The white marks are a byproduct of an untreated zinc surface (little or no chem treat) that comes into contact with moisture and carbon dioxide from the air. The white compound formed is called zinc carbonate. This defect is also known as condensation rust. It can be caused by failing to completely dry the chemical treatment or temper-rolling solution, as well as inadequate protection during the transportation of coils.