Cor-Ten steel cladding naturally evolves in appearance over time and is highly resistant to weather conditions. The oxide layer that forms on its surface protects the steel from corrosion. This patina continuously regenerates, allowing the façade to “protect itself,” resulting in a long-lasting, low-maintenance building envelope.

For architects and designers, Cor-Ten provides the possibility of creating continuous surfaces that interact visually with the surrounding landscape. Its gradual transformation and characteristic material language give the façade expressive decorative value and a unique identity.

Today, Cor-Ten is used in architecture much like a tailor-made textile—cut, folded, stretched, and embellished through perforation or surface treatments to highlight its flexibility and aesthetic qualities.

WHAT IS COR-TEN STEEL

Cor-Ten (weathering steel) is a trademark registered by U.S. Steel in the 1930s. The name comes from two intrinsic properties: COR (corrosion resistance) and TEN (tensile strength).

It is an iron–carbon alloy enriched with small amounts of copper, chromium, nickel, phosphorus, silicon, and manganese—less than 5% in total. The balanced composition of these alloying elements increases load-bearing performance while dramatically improving atmospheric corrosion resistance.

THE OXIDATION PROCESS

Cor-Ten is designed to reach a stable state of oxidation in which further rusting does not compromise structural quality, although the surface color continues to evolve.

However, the final shade cannot be predicted precisely because the material reacts to environmental conditions. The color and uniformity of the patina depend largely on:

• Local climate (temperature, humidity, wind exposure)

• Urban, rural, industrial, or marine surroundings

• Sun exposure and façade orientation

• Levels of SO₂ and chloride in the air

To form a stable protective coating, the steel requires alternating wet and dry cycles. In highly corrosive environments (industrial areas or coastal zones), the patina may not form correctly, and additional thickness may be required to ensure durability.

WHY COR-TEN FOR FACADE CLADDING

Originally developed for coal transport railway cars, Cor-Ten quickly became popular in architectural and artistic applications.

Its appeal lies in its natural color progression:

This ongoing transformation gives the building a “living,” evolving surface.

DESIGN AND FABRICATION FLEXIBILITY

Cor-Ten can be processed similarly to conventional steel:

• Mechanical or thermal cutting

• Folding, bending, forming

• Weldable with compatible strength between weld and parent metal

• Perforation, embossing, pattern cutting, or artistic customization

This makes it suitable for flat, curved, and faceted forms in architectural envelopes.

SUSTAINABILITY & ECONOMY

• Long lifespan and durability

• Minimal maintenance (often cleaned naturally by rainwater)

• No need for repainting or coatings

• Fully recyclable at the end of its service life

LIMITATIONS

Cor-Ten is not simply “rusted steel,” but a material that interacts with its environment and evolves over time. Its visual richness, durability, and low maintenance make it highly valued in architecture—provided that:

• The environment is suitable

• The assembly details are properly designed

• Drainage and material interfaces are carefully controlled

When used correctly, Cor-Ten allows façades to age with dignity and character, while reducing environmental impact and lifecycle costs.