Search and compare common metal surface preparation grades used for cleaning and abrasive blasting before protective coating.
| Grade | Method | Reference | General Preparation Description | Typical Use / Note |
|---|---|---|---|---|
| Sa 1 | Abrasive blast cleaning | ISO 8501-1 | Light blast cleaning. Loose mill scale, rust and foreign matter are removed; tightly adhering material may remain. | Lowest commonly specified abrasive blast cleanliness grade. |
| Sa 2 | Abrasive blast cleaning | ISO 8501-1 | Thorough blast cleaning. Most mill scale, rust and foreign matter are removed, with remaining material adhering firmly. | Used where a thorough but not near-white blast condition is specified. |
| Sa 2½ | Abrasive blast cleaning | ISO 8501-1 | Very thorough blast cleaning. Mill scale, rust and foreign matter are removed so that only slight staining or tightly adhering residues may remain. | Commonly specified for protective coating systems on steel. |
| Sa 3 | Abrasive blast cleaning | ISO 8501-1 | Blast cleaning to visually clean steel. Mill scale, rust and foreign matter are removed and the prepared surface has a uniform metallic appearance. | Highest ISO 8501-1 abrasive blast cleanliness grade. |
| St 2 | Hand / power tool cleaning | ISO 8501-1 | Thorough hand or power tool cleaning. Poorly adhering mill scale, rust and foreign matter are removed. | Used where abrasive blasting is not required or practical. |
| St 3 | Hand / power tool cleaning | ISO 8501-1 | Very thorough hand or power tool cleaning. The surface is cleaned more intensively than St 2, producing a more pronounced metallic appearance. | Higher hand/power-tool preparation level than St 2. |
| Flame | Flame cleaning | ISO 8501-1 | Flame cleaning is used to remove certain contaminants and loosely adhering material by controlled heating and subsequent cleaning. | Specialized preparation method requiring suitable process controls. |
| Wa 1 | Water jetting | Water-jet reference | Light water jetting preparation level. The resulting surface condition depends on the original steel condition and water-jet process. | Water jetting does not create the same surface profile as abrasive blasting. |
| Wa 2 | Water jetting | Water-jet reference | Thorough water jetting preparation level, with corrosion products and contaminants substantially removed. | Often selected where abrasive media recovery or contamination is a concern. |
| Wa 2½ | Water jetting | Water-jet reference | Very thorough water jetting preparation, with a high degree of removal of visible corrosion products and contaminants. | Exact visual acceptance depends on the applicable water-jetting specification. |
| Wa 3 | Water jetting | Water-jet reference | Very high water-jet cleanliness level approaching a visually clean prepared surface. | Water-jet appearance differs from abrasive-blasted steel. |
| SP 2 | Hand tool cleaning | SSPC / NACE | Removal of loose mill scale, rust, paint and other detrimental foreign matter using hand tools. | Comparable terminology may appear in project specifications using SSPC surface preparation designations. |
| SP 3 | Power tool cleaning | SSPC / NACE | Removal of loose mill scale, rust, paint and other detrimental foreign matter using power tools. | Power-tool preparation level; acceptance requirements should follow the specified standard. |
| SP 5 | Abrasive blast cleaning | SSPC / NACE | White metal blast cleaning. Very high removal of visible mill scale, rust, coatings and foreign matter is required. | High cleanliness preparation for demanding coating systems. |
| SP 6 | Abrasive blast cleaning | SSPC / NACE | Commercial blast cleaning. Most mill scale, rust, coatings and foreign matter are removed, with limited staining or tightly adhering residue permitted by the specification. | Common commercial-level blast preparation terminology. |
| SP 7 | Abrasive blast cleaning | SSPC / NACE | Brush-off blast cleaning. Loose material and contaminants are removed while tightly adhering material can remain. | Lower-intensity blast preparation used for selected coating applications. |
| SP 10 | Abrasive blast cleaning | SSPC / NACE | Near-white blast cleaning. Very high removal of mill scale, rust, coatings and foreign matter is required, with only limited staining permitted. | Common high-performance coating preparation designation. |
| WJ-1 | Water jetting | Water-jet reference | Highest water-jet cleanliness category in the commonly used WJ visual classification family, subject to the governing specification. | Water-jet cleanliness is visually different from abrasive blast cleanliness. |
Select a preparation grade in the reference table to view a concise planning summary.
Surface cleanliness grade describes what contaminants and corrosion products have been removed. Surface profile describes the roughness or anchor pattern produced by the preparation process.
Two surfaces can achieve a similar visual cleanliness level while having different surface profiles. Abrasive type, size, hardness, blasting pressure, angle and substrate condition can influence the resulting profile.
A coating specification may require several separate controls before paint application. Depending on the project, these can include visual cleanliness, surface profile, dust, soluble salts, surface temperature, ambient conditions and flash-rust control.
What is Sa 2½?
Sa 2½ is an ISO 8501-1 abrasive blast-cleaning grade representing very thorough blast cleaning, with only limited staining or tightly adhering residues permitted by the applicable visual criteria.
What is the difference between Sa 2 and Sa 2½?
Sa 2½ requires a higher degree of visual cleanliness than Sa 2. Sa 2½ is commonly selected for more demanding protective coating systems.
What is the difference between St 2 and St 3?
Both are hand or power tool cleaning grades in ISO 8501-1 terminology. St 3 represents a more thorough preparation than St 2.
Is Sa 3 the same as SP 5?
They are high-cleanliness abrasive blast preparation designations from different terminology systems. They should not be treated as interchangeable without checking the exact governing standards and project requirements.
Does blasting grade determine paint adhesion?
Preparation quality strongly affects coating performance, but adhesion also depends on surface profile, contamination control, coating selection, application conditions and other factors.
Does this tool calculate surface profile?
No. Surface profile must be specified and measured separately when required by the coating system.