Rust Converter vs Sandblast vs Epoxy Primer
เลือกตาม TOR + งบ + อายุงาน

**Only for niche maintenance — not primary work**. Rust converter (tannic acid or phosphoric acid) chemically converts Fe₂O₃ (red rust) into stable iron tannate / iron phosphate, but: • Only works on light rust (< 100 µm) where sandblast is impractical — rooftop tanks, undersides of operating bridges • Loose scale must still be removed by hand/power tool (SSPC-SP3) — cannot apply over flaking rust • Service life 3-7 years vs sandblast + epoxy 15-25 years • Never apply epoxy primer over residual acid without top-sealing — unreacted acid degrades the bond **Most Thai government TORs reject it** — Department of Highways, PEA, SRT specs require SSPC-SP10 (Near-White) minimum. Use rust converter only for budget maintenance or sandblast-inaccessible areas

Surface cleanliness levels after abrasive blasting — the two standards map to each other: • **SSPC-SP5 / NACE No. 1 = ISO Sa 3 — White Metal** — removes 100% of rust, mill scale, and old paint (silver-white steel). Required for immersion, atomic energy, offshore C5-M • **SSPC-SP10 / NACE No. 2 = ISO Sa 2.5 — Near-White Metal** — removes 95% (residual staining ≤ 5% area). Thai standard for C3-C4 industrial + petrochemical • **SSPC-SP6 / NACE No. 3 = ISO Sa 2 — Commercial Blast** — removes 67% (residual ≤ 33%). For general epoxy systems in C2-C3 • **SSPC-SP7 / NACE No. 4 = ISO Sa 1 — Brush-Off Blast** — loose scale only (rarely specified) **Anchor pattern (profile):** SP5/SP10 = 50-100 µm, SP6 = 35-75 µm. Measure with Testex tape (ASTM D4417 Method C) every 50 m² minimum

**Yes — always for outdoor service**. Zinc-rich epoxy (≥ 80% zinc dust in dry film, per ASTM D520 Type II + SSPC-Paint 20 Level 1) provides cathodic protection — zinc corrodes sacrificially before the steel. But: • **Direct UV exposure** → zinc oxide bloom → bond failure → top coat peels • Must be over-coated with epoxy intermediate (75-150 µm) + PU finish (50 µm) → standard 3-coat system • Zinc-rich alone ฿180-280/m² (75 µm DFT); full 3-coat ฿380-580/m² • Service life C5-M (offshore/petrochemical) 15-25 years vs non-zinc epoxy 8-12 years **Exception:** indoor C2 dry — zinc-rich + sealer is sufficient (2-coat ฿250-350/m²). Thai Highway bridges, SRT rolling stock, EGAT transmission towers (dark green livery) all use 3-coat

Three main zinc-rich primer brands sold in Thailand — differ by binder, film thickness, and price: • **ORAFON Zinc-Rich Primer** (Thailand made, distributed by Saha) — epoxy-polyamide binder, 85% zinc dry film, 75-100 µm DFT, ฿180-240/m², MOQ 20 L pail. Suits C3-C4 industrial structures + Thai government TOR • **ZINGA (Belgium)** — single-component cold galvanizing, 96% zinc, 60-120 µm DFT, ฿320-450/m². Substitute for hot-dip galvanizing on touch-up work • **Jotun Barrier 77** / **Hempel Avantguard 750** — premium organic zinc, 80-85% zinc, 60-80 µm DFT, ฿280-380/m². Meets Norsok M-501 + ISO 12944 C5-M offshore **Saha service:** we distribute ORAFON + provide 3-brand spec equivalence + TOR-matched submittal + 7-15 day lead time for 500+ m² jobs. Quote request — specify area, environment class, target service life

All-in-one — Saha provides rust treatment (galvanic + impressed current cathodic protection) + sells anti-rust primer (ORAFON + brand equivalents) + introduces vetted sandblast/coating contractors with C3-C5 track records: • **Cathodic Protection** (sacrificial anode + ICCP) — for underground / submerged / concrete-embedded steel • **Anti-rust primer ORAFON** — zinc-rich + epoxy-polyamide systems C3-C5 • **Surface prep partner** — SSPC-QP1 certified subcontractors with 5+ year working history (BMA bridges, SRT locomotives, EGAT transmission towers) **One-stop quote** — scope within 24 h, all-in price + lead time + ASTM/ISO/TIS compliance warranty. Free site survey within Bangkok metropolitan area