Sa 2.5 is a visual cleanliness grade in ISO 8501-1 (Preparation of steel substrates before application of paints). Inspectors compare the blasted steel with the ISO photographic plates. It is not a paint brand and not a machine model. It is how clean the steel must look before primer.
ISO 8501-1 lists blast grades Sa 1 (light), Sa 2 (thorough), Sa 2½ / Sa 2.5 (very thorough) and Sa 3 (visually clean / white metal). Hand-tool grades St 2 and St 3 sit beside them when blasting is not possible.
In practice Sa 2.5 means mill scale, rust and old coatings are gone. At least about 95% of each area looks clean, bright metal. Slight shadows, streaks or stains may remain. People call this near-white metal. North American specs usually write SSPC-SP 10 / NACE No. 2 for the same intent.
Most industrial coating systems in India specify Sa 2.5: zinc-rich primers, high-build epoxies, tank linings, structural steel, pipelines, bridges. Sa 3 is slower and costlier. Specify Sa 3 only when the coating data sheet or client spec demands white metal.
- Remove oil and grease first (SSPC-SP 1 style solvent clean). Blasting does not hide grease.
- Match abrasive to the required profile. Copper slag and steel grit cut mill scale well for Sa 2.5 on structural steel.
- Hold 90–100 psi at the nozzle when the spec allows. Low pressure leaves mill scale.
- Check cleanliness with ISO 8501-1 plates in good light. Check profile with a surface profile gauge.
- Coat before flash rust. Humidity and dew point decide how long the steel stays blast-clean.
BLAST APEX crews blast to Sa 2.5 / Sa 3 on tanks, structures and hulls from Mahape and Bhiwandi. Equipment pages below size the pot, abrasive and gauge for the same job.