An engineer's coating spec for a water tank says SSPC-SP 10 with a 2-3 mil angular profile before a zinc-rich primer.

Achieving the Profile (2–3 mils angular):

1. Abrasive: Use angular steel grit (G25–G40) or crushed slag/garnet (30/60 mesh). Round shot cannot produce an angular anchor pattern.
2. Equipment: Nozzle pressure 90–100 psi at the nozzle (verify with hypodermic gauge). Use a Venturi (long-barrel) nozzle (#6–#8 orifice).
3. Technique: Maintain 18–24" standoff, 50% overlap, uniform speed. Avoid "polishing" (dwelling too long), which rounds peaks and lowers profile.
4. Cleanliness: Blast to SSPC-SP 10 (Near-White). No visible oil, grease, dust, mill scale, rust, or coating. Stains/shadows ≤5% per unit area. Blow down with clean, dry, oil-free air (test per ASTM D4285) immediately after blasting.

Proving It (QC Hold Points):

1. Surface Cleanliness: Visual comparison to SSPC-VIS 1 / ISO 8501-1 (Sa 2.5). Photograph with scale.
2. Profile Depth (Mils): ASTM D4417 Method B (Replica Tape) — Required for zinc-rich primers. Burnish X-Coarse tape (0.8–4.5 mils) on 3–5 representative spots per 100 ft². Read with calibrated spring micrometer. Report peak-to-valley average. Alternative: ASTM D4417 Method C (Digital Profile Gauge) calibrated to replica tape on this* steel. Zero on glass.
3. Profile Angle/Shape: ISO 8503-1/2 (Comparator) or visual per SSPC-VIS 3. Must show sharp, angular "V" peaks, not rounded "U" valleys.
4. Dust Residue: ISO 8502-3 (Dust Tape Test) — Rating ≤2.
5. Soluble Salts: ISO 8502-6 / SSPC-TU 4 (Bresle patch or ChlorTest) — < 5 µg/cm² (chlorides) typical for immersion/zinc primer. Non-negotiable.*

Documentation: Submit Daily Blast Report with: abrasive certs, nozzle pressure logs, replica tape readings (with tape affixed to report), dust/salt results, photos, and inspector sign-off. Hold for engineer review before priming.

Critical: Zinc-rich primers (inorganic especially) require angular profile for mechanical lock and electrical contact. Rounded profile = premature failure. If specs conflict (e.g., "SP 10" but "2–3 mils" on thin steel), stop and get written clarification — over-blasting burns through plate.

To achieve and verify SSPC-SP 10 (Near-White Metal Blast) with a 2–3 mil angular profile for a water tank prior to zinc-rich primer application:

Process:

1. Surface Preparation: Use angular abrasive (e.g., crushed slag, steel grit, or aluminum oxide) at 90–100 psi nozzle pressure. Blast to remove all visible oil, grease, dirt, mill scale, rust, and coatings. SSPC-SP 10 allows only very light staining (≤5% per 9 in²) from rust or mill scale in pits — no visible residue. Inspect visually per SSPC-VIS 1/NACE VIS 1 standards.
2. Profile Measurement: Use replica tape (e.g., Testex Press-O-Film) or digital profilometer per ASTM D4417 Method C (replica tape) or B (digital). Take ≥3 measurements per 100 ft², avoiding edges and welds. Target 2.0–3.0 mils (50–75 µm). Angular abrasive ensures the required profile shape for mechanical adhesion.
3. Documentation: - Record blast pressure, abrasive type/size, nozzle distance, and travel speed. - Log profile readings with location, time, and technician ID. - Take pre- and post-blast photos (per SSPC-PA 2). - Submit a NACE/SSPC-certified inspector’s report (if required by spec) or use a qualified coating inspector per ASTM D3276.

Critical Notes:

• Water tanks (especially potable) often require additional cleanliness (e.g., SSPC-SP 12/NACE No. 5 for welds) and solvent cleaning (SSPC-SP 1) pre-blast.
• Zinc-rich primers demand strict profile control — too low risks adhesion failure; too high causes thin film coverage.
• If the tank is for potable water, confirm the zinc-rich primer is NSF/ANSI 61 certified and consult a licensed corrosion engineer or NACE-certified specialist — this is not a DIY task. Improper prep risks tank failure, contamination, or costly rework.

Bottom Line: Follow SSPC-PA 2 for blast cleaning verification and ASTM D4417 for profile. Use third-party inspection if spec requires it. Never skip documentation — proof is as critical as the blast itself.