ISO 8501-4:2020 specifies a series of preparation grades for steel surfaces after removal/partial removal of water-soluble contaminants, rust, previous paint coatings and other foreign matter by high-pressure water jetting. The various grades are defined by written descriptions together with photographs that are representative examples within the tolerances for each grade as described in words.

This document specifies both initial surface conditions and after-cleaning flash rust grades, also defined by written descriptions together with representative photographic examples.

This document applies the cleanliness of the surface to its visual appearance.

Consideration in addition to visual appearance is given to invisible contaminants and roughness or profile. Physical and chemical methods for testing for soluble salts and other invisible contaminants on the visually clean surface are found in the ISO 8502 series. The roughness or profile characteristics of the surface are found in the ISO 8503 series.