Pre-oxidized weathering steel (such as COR-TEN or weathering steel that undergoes factory-accelerated rust treatment) has a stable rust layer (also known as a "stabilized rust layer") formed before leaving the factory through chemical or natural means. Therefore, its color typically does not change significantly after installation. This is specifically demonstrated as follows:
1. Discoloration Characteristics of Pre-oxidized Weathering Steel
Factory State: The surface exhibits a uniform reddish-brown, dark brown, or blackish-brown color (depending on the treatment process).
Post-Installation Changes:
Minor Adjustments: During the initial exposure period (1-6 months), the color may slightly darken or undergo minor adjustments due to environmental humidity, pollutants, and other factors, but the overall hue remains consistent.
Long-Term Stability: After 6 months to 1 year, the rust layer is completely stable, with minimal color change (unless in extremely harsh environments).
2. Factors Affecting the Speed of Discoloration
Ambient Humidity: High humidity (such as in coastal areas) may accelerate the initial adjustment of the rust layer.
Pollutions: Acid rain, salt spray, or industrial pollutants may cause localized color variations.
Rainwater erosion: Frequent rain can remove unstabilized rust, potentially prolonging the homogenization process.
3. Comparison with Ordinary Weathering Steel
Characteristics: Pre-oxidized Weathering Steel
Ordinary Weathering Steel
Initial Color: Uniform rust color from the factory
Metallic color (silver-gray)
Color Change Cycle: Fine-tuning after 1-6 months after installation, followed by stabilization
Gradual rusting over 6 months to 3 years, with uneven color
End Effect: Uniform rust color controlled by design
Naturally occurring mottled rust color
Maintenance Requirements: No maintenance required
Wait for the rust layer to stabilize (may take several years)
4. How to Ensure Color Consistency
Choosing a Reliable Supplier: Ensure the factory pre-oxidation process is mature (e.g., spraying a rust promoter followed by natural weathering).
Post-installation Protection: Avoid initial contact with acids and alkalis or frequent human friction.
Design Compatibility: Accept minor natural adjustments and avoid being overly sensitive to color variations.
5. Special Needs
If complete discoloration is required: Pre-oxidized weathering steel will still adjust slightly to the environment. If absolute discoloration is required, stainless steel or spray-coated weathering steel should be used (although this will sacrifice its inherent corrosion resistance).
Accelerated stabilization: Regularly spraying with water (simulating rainwater) after installation can help the rust layer settle more quickly and evenly.
