Characteristics of Corten Weathering Steel

Corten is an alloyed steel product and was developed and patented by US Steel. By including a small amount of copper CU, Chrome Cr and Nickel Ni to the steel the rust patina formation builds up an impervious layer which blocks the steel pours and protects the inner core from further corrosion and rust.

For this rust to form the material requires continuous periods of wet and dry- therefore burying or immersing the product in water will not allow the formation of this protection. It may also be important to ensure there is adequate ventilation to the rear of the panels.

While the rust surface is developing, the rain runoff will carry ferrous particles which may well stain surfaces below or react with dissimilar metals. Porous surfaces such as raw concrete would be most susceptible to this staining. Managing this runoff would be an important consideration when using this product.

Methods include:

  • Capturing the runoff and directed to less noticeable areas such as flower beds or scoria drains.

  • Sealing the concrete or the use of non-porous materials.

  • Installing a stainless grate drain directly below the drip zone.

The copper enriched run-off will also affect dissimilar metals and must be managed in a similar approach to Copper cladding run-off. Protection to existing Zincalume or Colorbond roofs can be achieved with stainless steel flashings or bitumastic membranes to illuminate water contact between them.

The lifespan of Corten is vague and in most cases undocumented. The best available tests we have found have been carried out by Arcelor Mittal (who purchased the rights from US Steel) in coastal, industrial and rural applications. These tests were conducted over a period of 16 years and it was found that initially the sample thickness increased. The rust penetration after this period of 16 years was only 0.02mm for coastal and 0.04mm for Industrial areas. In marine environments stable oxide films may form on the steel provided chlorides are regularly washed by rain or fresh water. Find out more here.

Applications in salt spray environments are not recommended unless material is painted. Installation in the proximity of salt chlorinated swimming pools is also not recommended. In this case we would recommend an alternative water treatment system such as Bionizer which is salt free and safer on a whole. Archclad have been supplying Corten for approximately 7 years as a cladding product and offer the following recommendations to consider when using Corten for cladding applications - to assist with longevity and material performance:

  1. Manage water capillary action at end laps and flashing junctions.

  2. Ventilate cladding from the rear- to allow for Drying periods.

  3. Use hollow panels such as Archclad Express panels to assist with item 2 above.

  4. Do not use Standing Seam or Flatlock on a continuous substructure as this prevents the rear from drying out and may cause sweating between surfaces- the use of a trapezoidal substructure may assist with air-flow or another profile completely.

  5. Cut back overhanging trees which may prevent material from achieving the wet/ dry cycles.

  6. Avoid gutters and downpipes which will be constantly wet- in Corten.


As none of the Steel Mills producing Corten offer a warranty on the lifespan of the product, Archclad™ draws your attention to the fact that there is no material warranty offered on Corten - other than standard of installation and performance of new Corten materials as tested to Australian Standards.

For further information contact Archclad™