specific and controllable environmental conditions are required to form a uniform, dense, stable, and aesthetically pleasing natural patina on SPA‑H weathering steel. Below are the clear, practical requirements:
1. Atmospheric environment
Preferred condition:Mildly industrial or rural atmosphere with moderate levels of oxygen and mild pollutants (e.g., low SO₂).This promotes the formation of stable, dark brown patina.
Not suitable:Severe coastal salt spray or strong acid/alkali industrial zones→ cause loose, patchy, unstable rust.
2. Humidity & wet‑dry cycles (most critical)
Required:Alternating wet‑dry cycles (surface fully wetted, then fully dried).Typical ideal cycle: 12–24 hours per cycle.
Must avoid:Long‑term continuous soaking or permanent high humidity→ produces powdery, non‑protective rust.
3. Ventilation
Required:Good natural or forced ventilation to ensure even and complete drying.
Poor ventilation leads to uneven color, streaks, and slow maturation.
4. Sunlight & temperature
Preferred:Moderate sunlight (UV radiation) to accelerate oxidation and uniform color development.
Temperature: 10–30°C is most favorable.Below 5°C, patination becomes very slow.
5. Rain & drainage conditions
Required:Vertical installation or good slope to ensure rapid water runoff.
Must avoid:Horizontal surfaces, concave areas, or gaps that trap water.
6. Cleanliness
The environment should be free from frequent oil, cement, mortar, or strong chemical contamination.
These contaminants block oxidation and cause color unevenness.
