Residual dust on blast-cleaned steel acts as a "bond-breaker" between the substrate and the protective coating. Even a thin layer of microscopic particles can reduce adhesive strength, leading to premature delamination or blistering. Furthermore, dust is often hygroscopic; it can trap moisture against the steel, accelerating corrosion under the paint film, often before the asset even enters service. ISO - International Organization for Standardization INTERNATIONAL STANDARD ISO 8502-3
Very low dust level; particles are barely visible to the naked eye.
Mastering the ISO 8502-3 Dust Level Chart: The Ultimate Guide to Surface Cleanliness
The standard remains the current global benchmark for assessing dust on steel surfaces before painting. While it was last confirmed in 2022, the methodology and pictorial references established in the 2017 update continue to serve as the industry standard for quality control in 2024 and beyond. iso 85023 dust level chart pdf updated
Here is the precise, actionable information you need:
The standard evaluation relies on cross-referencing your physical tape sample against the pictorial standards and tables defined within the standard. 1. Dust Quantity Classification (Ratings 1 – 5)
The chart is divided into two main assessment axes: Residual dust on blast-cleaned steel acts as a
Dust particles act as contaminants that prevent paint from wetting the surface properly, leading to pinholes and poor adhesion. Furthermore, dust particles are often hygroscopic (moisture-absorbing), which traps moisture between the steel and the paint, leading to osmotic blistering and corrosion.
While some related standards in the 8500 series (e.g., ISO 8501-3) have been updated to 2025 editions, the status of ISO 8502-3 remains at the 2017 revision. However, caution is advised: some national databases have marked the 2017 version as "withdrawn," a move that often precedes the publication of a new revision. For mission-critical applications, it is essential to verify the active status of the standard with your national standards body or the official ISO website.
Press the tape firmly onto the steel surface. Remove Tape: Carefully remove the tape from the surface. Here is the precise, actionable information you need:
An accurate dust level assessment ensures high-performance industrial coatings stick to steel surfaces and prevent premature corrosion failure.
| Coating Environment | Acceptable Dust Quantity | Max Particle Size | Recommended Action | | :--- | :--- | :--- | :--- | | | Class 1 or 2 | <100 µm | High-pressure fresh water rinse before coating. | | Chemical Storage Tank Lining | Class 1 | <50 µm | Vacuum cleaning + tack rag immediately before coating. | | Bridge Structural Steel (Atmospheric) | Class 3 | <200 µm | Compressed air blow-down acceptable. | | Pipes buried in soil | Class 3 | <300 µm | Minor dust acceptable if primer is high-build. | | Recreational equipment / handrails | Class 4 | <400 µm | Cosmetic only – structural risk low. |
Along with quantity, the inspector must identify the particle size: