What is NACE 2 / SSPC-SP10?
SSPC-SP10 (also known as NACE No. 2) defines a surface preparation grade called « near-white metal blast cleaning ». The standard requires that 95 % of the surface be free of all visible mill scale, rust, coating and contaminant — leaving a uniform grey metal, slightly rough.
This is the reference standard for demanding industrial applications: immersion coatings, ISO 12944 C5 anti-corrosion systems, high-adhesion composite repairs. Below this grade (SSPC-SP6 « commercial blast » or SSPC-SP3 mechanical prep), coating service life drops by 50 to 70 %.
The anchor profile: why 75-100 µm?
Grit blasting does not just clean: it creates a roughness (anchor profile) that lets the coating grip mechanically. For epoxy coatings, the optimal profile is 75 to 100 µm (3-4 mils). Too low (< 50 µm), adhesion is insufficient. Too high (> 125 µm), peaks are not covered by the planned DFT and create preferential corrosion points.
- Measure the profile with Testex Replica Tape (coarse or X-coarse grade)
- Check on at least 3 zones per 10 m² of surface
- Document the values in the QA/QC sheet
Choosing the abrasive
The choice of abrasive determines the profile, productivity and dust. Steel grit (G16/G40) offers the best profile for industrial applications — hard, reusable, low dust emission. Garnet (natural mineral) suits sites needing a non-metallic abrasive (food, nuclear). Crushed glass suits delicate surfaces (stainless, aluminium).
The 5 mistakes that ruin adhesion
Even with perfect SSPC-SP10 blasting, certain post-prep mistakes cancel the coating's benefit. Here are the most common ones observed on Canadian industrial sites:
- Time exceeded: applying primer more than 4 h after blasting (flash rust)
- High humidity: blasting at > 85 % relative humidity or surface < 3 °C above dew point
- Dust contamination: not blowing off with clean compressed air before application
- Oily surface: touching the surface with dirty gloves or skipping the second degreasing
- Dirty-solvent degreasing: reapplying contaminants with a used rag
Conclusion
NACE 2 / SSPC-SP10 preparation is not a cosmetic step: it is the foundation of the manufacturer warranty and the planned service life. Respecting the anchor profile, the time between blasting and application, and the hygrometric conditions is non-negotiable for a high-performance anti-corrosion system.
Hicham M, P Eng, PMP
Engineer and project manager (PMP) at Induscoat Canada. Over 16 years of experience in industrial coatings, composite repairs and wear protection on mining, energy and petrochemical sites in Canada and internationally.