This is a qualitative visual comparison ranging from 1 to 5 based on pictorial references: Smallest amount of surface dust.
These particles, if left untreated, act as a wick for moisture absorption and destroy coating adhesion, leading to premature failure like osmotic blistering or delamination. iso 85023 dust level chart pdf updated
ISO 8502-3 specifies a simple, field-friendly method using (commonly a transparent Scotch tape of defined tackiness) to lift dust from a prepared steel surface. The tape is then applied to a contrasting background (typically a white or black card), and the extracted dust is compared against a standardized reference scale. This is a qualitative visual comparison ranging from
| Dust Class | Maximum Particle Size (µm) | Typical Quantity (particles/cm²) | Visual / Tape Appearance | Typical Coating Suitability | |------------|----------------------------|----------------------------------|--------------------------|-----------------------------| | | < 50 | 1–5 | Almost invisible, very few tiny specks | High-performance systems (epoxy, polyurethane, marine) | | 2 | 50 – 100 | 6–20 | Scattered small dots, clearly visible on tape | Industrial coatings (alkyd, epoxy mastic) | | 3 | 100 – 200 | 21–50 | Many medium-size particles, no clustering | Low-risk environments only (non-immersion) | | 4 | 200 – 300 | 51–100 | Dense particles, some clusters visible | Not acceptable for critical coatings | | 5 | > 300 | > 100 | Heavy dust layer, clumps | Rejection – requires re-blasting or cleaning | The tape is then applied to a contrasting
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