Shot blasting vs grinding before painting

• Do not remove mill scale — mill scale (hot-rolling oxide scale bonded to steel) has a different electrical potential from the base steel and triggers galvanic corrosion under the paint. Grinding and brushes flatten it but do not remove it.
• Do not create a uniform profile— the roughness profile left is irregular and difficult to control, compromising coating adhesion.
• Not traceable — there is no cleanliness grade standard equivalent to the Sa grades of ISO 8501-1 for grinding; the result depends on the operator and cannot be certified.

• Hydrogen embrittlement risk — on high-strength steels, acid pickling can introduce hydrogen into the crystalline structure, reducing material toughness.
• No mechanical anchor profile — acid dissolves the oxide but leaves a chemically clean and relatively smooth surface; paint adheres by surface tension, not mechanically.
• Toxic waste generation— pickling baths exhaust their capacity and must be treated or disposed of as hazardous waste, with high cost and logistical complexity.
• Rapid re-rusting without immediate coating — pickled steel is highly reactive and can re-rust within hours if the coating is not applied immediately.

• Complete mill scale removal — abrasive projected mechanically at high speed detaches and removes mill scale without acids. It is the only process that guarantees complete removal.
• Controlled roughness profile (Ra / Rz) — abrasive type and size determine the profile. That profile can be specified, measured and certified to the coating standard.
• Traceable cleanliness grade (Sa / SP)— ISO 8501-1 and SSPC/AMPP define grades Sa 2, Sa 2½ and Sa 3, which can be visually verified and certified in the quality record.
• Standardisable and repeatable process — parameters (abrasive, speed, passes) can be fixed and reproduced, guaranteeing the same result across the entire production run.