Rust formation on Corten steel occurs due to the combination of iron, water, and oxygen. It forms a stable rust layer (patina) under the influence of alternating wet and dry conditions. This mainly happens in areas where there is sufficient oxygen. In the ground, this process occurs much more slowly, as there is less oxygen available.
Corten steel is supplied in a grey metal colour and is not yet fully rusted upon receipt. Sometimes small rust spots are already visible, but once the product is placed outdoors, the rusting process begins automatically – usually within two weeks to months. The entire process takes one to two years and results in a robust, protective rust layer with a warm appearance.