Sandblasting (Sa 2.5)

Sa 2.5 is the near-white-metal abrasive blast-cleaning grade in ISO 8501-1, the surface-preparation standard most marine coating systems specify before primer. After blasting, the steel must show no visible oil, grease, mill scale, rust, or old coating, with only faint shadows, streaks, or stains over at most about 5% of each section of surface. It is the practical workhorse grade: zinc-rich primers, the IMO PSPC ballast-tank scheme, and most epoxy systems are qualified to it. Sa 2.5 is judged visually against the pictorial reference photographs in ISO 8501-1, and the inspector pairs it with a surface-profile (anchor pattern) measurement, typically 50 to 85 microns for marine epoxy.