Corten™ steel – Your questions answered

The rate of oxidation and the orange color can vary on the same project depending on its context and its microclimate. The oxidation period can last from several months to several years.

If you have a layer of scale, your Corten™ steel may take up to 2 years to have a nice even layer of orange (depending on dry and wet periods) as it has to penetrate the scale that covers the Corten™ steel.

On the contrary, if you remove the scale, you will have an orange layer after a few days since the steel will be bare and will not have any protection.

Among the unique aspects of Corten™ steel: the changes in its exposed surface over the years. It goes from an initial dark gray finish to an orange patina in a few weeks. The patina continues to evolve and reaches a definitive dark brown color after several years, depending on local weather conditions.

The rate of change and final color of the Corten™ steel depends on the surrounding atmospheric conditions. Sulfur-dense atmospheres accelerate the oxidation process and give a darker patina. Frequent cycles of wet and dry conditions accelerate oxidation. To obtain a uniform and homogeneous coloring, the surface must be sanded before being subjected to atmospheric conditions. To obtain a more industrial finish, a simple cleaning with water will be sufficient. Industrial oxidation takes much longer to create.

During the skating process of Corten™ steel, rust stains may settle on surrounding surfaces such as glass, natural stone, pavers, aluminum, etc. This is called “bleeding” or “trickling”.

These stains can be avoided if the structure is designed so that water does not run off these surfaces but onto surfaces that are less susceptible to staining. If necessary, clean these stains by rubbing with hot water regularly. This bleed is mainly stable iron oxide which is not dangerous for the environment, vegetation or wildlife.

The oxidation of steel is considered to have reached its maturity when it hardly causes any dirt or marks to the touch. The oxide layer is then strong enough not to stain clothing or surrounding surfaces.

If the Corten™ steel skating process is not stabilized, to the touch, it may leave marks on your hands or clothing or exterior item. It can be difficult to remove some stains from fabric due to the wide range of fabrics used in manufacturing today. However, if this happens to you, simply clean the fabric or material with water and scrub. If the stain is still present, use a biodegradable powdered stain remover such as Oxy Clean and wash with hot water. Always test on a small section and follow the manufacturer’s instructions.

The more often you clean your ”bleeding” patina, the easier it will be to remove it.

Corrolux does not recommend the use of chemicals to activate and accelerate rust formation as they are often aggressive to Corten™ steel and can cause damage if used incorrectly. We are currently working on the design of a product line for treating and finishing Corten™ steel. We will inform you when it is available.

Steel is not always easy to install. This requires good preparation, a straight floor and good working tools. All of our pieces are computer cut and therefore sound perfectly straight. For best results when assembling, take the time to place each piece perfectly straight and aligned otherwise you may have problems with the assembly.

Even for Corten™ steel, excess moisture should be avoided as it disrupts its surface layer and can result in the steel peeling. Moreover, the presence of salt destabilizes the protective layer of the material. In both situations, there will be repeated deterioration of the oxide layer resulting in premature wear of the steel.

In order to address premature degradation in such a context, custom designs can be made by adapting the thickness of the Corten™ steel and thus guaranteeing an extended life.

Corrosive atmospheres, such as distances within one kilometer of coastal waters, should be avoided as high chloride concentrations will damage the patina and increase the corrosion rate.

To promote the appearance of oxidation naturally, the ideal conditions are a frequent alternation of wet/dry periods and good aeration. It should be noted that it is very difficult to oxidize Corten™ steel on the inside.

Scale is a dark gray layer generated – and very difficult to remove – on the surface of steel sheets. It occurs during its manufacture. The patina will break through this layer of scale but it is a long process. Depending on your choices, this layer can be removed with a sandblasting.

When placed indoors, Corten™ steel will not oxidize. Although it is predominantly a material for exterior use, more and more architects and designers are looking to incorporate Corten™ steel into their interior design projects.

For residential projects, it is possible to place the product outside to oxidize it until you obtain a platinum that will be to your liking. Then place it in the location of your choice. Be careful, since there is no protection, if the patina is contaminated (glass of water, wine), it may remain marked.

For commercial projects or if you want a perfect finish, Corrolux can offer you this service. For a quote, contact us via info@corrolux.com.

Yes, this type of steel can be oxidized in electrolytic contact with copper, lead or tin. It can also cause the oxidation of aluminum, stainless or zinc. It is therefore necessary to separate each of these materials during design/installation.

Yes, it is possible to paint Corten™ steel. If there is a scratch on the paint, the patina will fill the hole almost instantly and prevent the steel from degrading faster in that area.

Corrolux provides stainless steel hardware (screws, bolts, etc.) as it is more durable and unbreakable. Such Corten™ steel hardware could not guarantee the same mechanical strength. However, you can paint these items if you don’t like their appearance.

Yes, these are synonymous terms.

In November 1997, ASTM modified and improved the corrosion resistance specifications by emphasizing an “atmospheric corrosion index” that can be calculated to compare the relative service life of different grades and heat batches of corrosion resistant steels. It also required each ASTM grade to meet a minimum atmospheric corrosion index of 6.0, effectively improving the quality of the weathering steels produced. Corten steel products normally have a nominal atmospheric corrosion rating of 8.0.

Note that Corten™ steel is not suitable for use in a high temperature environment (above 200 degrees)

Weathering steels are a family of ASTM specifications.

ASTM specifications are A588, A242, A606-4, A847, A871-65 and A709-50W. The main branded product is Corten™. The selection of a particular ASTM weathering steel specification depends on the type of product desired. ASTM A588 covers structural shapes, plates and bars. ASTM A242 covers the steel plate to one-half inch thickness. ASTM A606-4 covers steel sheets and coils and ASTM A847 is for weathering steel pipes and tubes. ASTM A871-65 also covers the plate, but with a minimum yield strength of 65ksi.

There are essentially two types of Corten™ steel: Type A and Type B Corten™. They differ primarily in the amounts of phosphorus alloyed into the mix.

CORTEN™ A / S355J0WP STEEL: generally referred to as “Phosphorus Steel” (P), an element that primarily promotes protective oxidation. It is mainly used for architectural applications. Corten™ A steel is typically produced in sheet or coil form (1.0 mm to 12 mm) and has applications in cladding and ductwork. The increased phosphorus and copper content contributes to the production of the oxidized patina that forms on the surface of the metal, reducing its susceptibility to rust and corrosion.

CORTEN™ B / S355J2W STEEL is used for highly stressed structures. This special steel can also be supplied with low-temperature resilience. Corten™ B steel is most commonly produced in plate form (15 mm to 50 mm).

CORTEN™ STEEL A and B meet and/or exceed the requirements of ASTM A606 Type 4.