What the standard describes
ISO 8501-1 sets written and pictorial assessments for the preparation of steel, especially hot-rolled steel, before coating. Sa applies to abrasive blast-cleaning; it does not by itself assess surface profile or invisible contamination such as soluble salts.
Meaning of the grades
- Sa 1: light blast-cleaning — loose mill scale, rust, coating and foreign matter are removed.
- Sa 2: thorough blast-cleaning — most firmly adhering residues must not remain visible on close inspection.
- Sa 2.5: very thorough blast-cleaning — remaining residues are limited to slight stains or streaks.
- Sa 3: blast-cleaning to visually clean steel — the surface has a uniform metallic colour.
The specification selects the grade
There is no universal correct grade. The project or coating manufacturer selects it for the system and exposure, and inspection may also include profile, dust, salts and climate conditions.