METAL TYPES: COR-TEN STEEL

Weathering Steel Designed to Evolve.

Architectural Strength with a Living Finish

At CSI Architectural Metal, Cor-Ten steel provides architects and designers with a high-strength material distinguished by its naturally evolving surface. Also known as weathering steel, Cor-Ten is engineered to form a dense, self-protecting oxide layer when exposed to the atmosphere.

Its surface progresses from warm gray-orange tones through amber and brown before developing a rich, deep rust-red appearance. Once stabilized, the protective patina continually renews itself during alternating wet and dry conditions, helping protect the underlying steel.

A Finish That Evolves Naturally

Cor-Ten develops its characteristic appearance through atmospheric oxidation. As the protective layer matures, the surface transitions through increasingly rich, warm tones.

Protection Built Into the Surface

Unlike ordinary carbon steel, Cor-Ten is designed to resist continued corrosion after its initial oxidation period. Its dense oxide barrier seals the surface and helps prevent deeper rust penetration.

When properly detailed and used in appropriate environments, weathering steel can provide a service life of 80–100+ years.

Important Design Considerations

Cor-Ten performs best in environments that experience periodic wet-and-dry cycles. It is generally not recommended for continuously wet, submerged, or marine exposures.

Built for Architectural Expression

Designed for Precision Fabrication

Cor-Ten can be cut, welded, folded, and fabricated using standard steel techniques, making it adaptable to a wide range of custom architectural forms.

Proper detailing is particularly important. Drainage, panel overlap, and edge isolation should be carefully considered to help control initial runoff and prevent staining of adjacent materials.



Cor-Ten may also be supplied pre-weathered, providing greater initial color stability and reducing early-stage surface runoff.

Low Maintenance After Stabilization

Once the protective patina has fully stabilized, Cor-Ten requires virtually no routine surface maintenance. Initial weathering—typically occurring over approximately 6–12 months—may produce minor runoff as the oxide layer develops.



Periodic inspection of drainage and attachment points can help maintain consistent aging and long-term performance.

Why Architects & Builders Choose Cor-Ten Steel