Why Surface Preparation Matters
Surface preparation is the most critical factor in coating success. Studies show 60-70% of coating failures trace back to inadequate preparation. ISO 8501-1 defines specific surface cleanliness grades that must be achieved before painting.
ISO 8501-1 Blast Cleaning Grades
| Grade | Description | Visual |
|---|---|---|
| Sa 1 | Light blast – loose contaminants removed | Dull gray, staining remains |
| Sa 2 | Thorough blast – nearly all removed | Uniform gray, spots may remain |
| Sa 2.5 | Very thorough – ≤5% staining | Near-white metal |
| Sa 3 | Blast to visually clean steel | Uniform white metallic |
Sa 2.5: The Industry Standard
Sa 2.5 is the most commonly specified grade. The surface is free of all visible oil, grease, rust, mill scale. No more than 5% may show staining residues. Surface profile typically 50-75 μm.
When Sa 2.5 Is Required
- Marine environments and offshore structures
- Immersion service (tanks, buried foundations)
- High-performance coating systems (epoxy, zinc-rich)
- 15-25 year design life protection
- Steel bridges in corrosive environments
Sa 3: The Premium Grade
Sa 3 achieves 100% clean, uniform metallic surface with no staining. Required for thin-film coatings, aggressive chemical immersion, and food-grade equipment.
Surface Profile Requirements
| Coating Type | Recommended Profile (Rz) |
|---|---|
| Epoxy primer | 40 – 65 μm |
| Zinc-rich primer | 50 – 75 μm |
| Heavy-duty epoxy | 50 – 85 μm |
| Thermal spray | 75 – 125 μm |
Abrasive Media Selection
| Abrasive | Profile Range | Best For |
|---|---|---|
| Steel grit (G25-G40) | 50 – 100 μm | Heavy structures |
| Copper slag | 50 – 75 μm | Cost-effective |
| Garnet | 40 – 80 μm | Stainless, offshore |
Need Steel Products for Your Project?
CoreMetal Steel (Xi’an Coremetal Steel Co., Ltd.) is a professional steel and metal materials supplier based in Xi’an, China. We export to 60+ countries with ISO 9001 certification. Contact us today for competitive pricing and technical support.
Contact: Tracy | Email: tracy@coremetalsteel.com | Phone: +86 18291910632