Corten Steel

Corten Steel

General requirements applicable to all Metalco’s products in any material

Upon receipt of the goods, where it is not possible to place and/or install them within a few days, they must always be removed from plastic (nylon) packaging to allow ventilation and prevent the formation of condensation that can irreparably damage the product. Particularly, the packaging should always be removed immediately if it is not possible to keep the goods in a covered place protected from sunlight.

Features and cycle of aging Metalco Corten

Metalco activates the maturation of corten steel, using a system of natural oxidation through weathering, thus favoring non-invasive techniques for the environment. This natural system, gives corten steel a particular non-uniform aspect and different shades of color. Particularly, the nuances of color typical of corten steel are more visible in weld areas, since the formation of the patina on these points is slower.

The shades of color, therefore, are not a defect.

N.B: the reproduction of the shades shown on paper is only indicative. Upon request, platelet samples can be provided.

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Corten steel, thanks to the process of maturation and oxidation that characterizes it, is considered a “live” material, meaning the shades and hues may vary over time depending on the shape of the object, the position in which it is installed and according to the cycles of weathering which the object undergoes.

Warning: The average period during which the natural cycle of maturation of corten “stabilizes,” giving the material a dark brown shade typical of oxidized corten, is about 12 to 18 months, in the presence of suitable weather conditions. During this stage of maturation, the corten may leak oxide (“washout”), which may stain surfaces where the products are located. For corten, this is considered a natural and physiological behavior of the material.

To reduce the loss of oxide, Metalco uses a special “ANTI-WASHOUT” treatment which may be requested by the customer, at extra cost: this treatment does not completely block the losses, but significantly decreases the oxide leak, giving the product a darker appearance and “finish.”

As indicated above, the laying of corten products on valuable and/or porous surfaces (e.g. marble, granite, etc..) must be carefully evaluated. Also in the case of Anti-washout treatment,  it may be advisable to use, alternatively, galvanized and painted steel with the “corten color” developed by Metalco.

In the vicinity of the sea, the harsh salty air can lead to the formation of oxides on the surfaces that result in the appearance/color looking different to normal. This does not affect good mechanical strength of the material.


Appearance/shades of naturally oxidized product at the time of delivery (approximately 2 months of natural oxidation).Corten maturation 1


Appearance/shades of naturally oxidized product after about 4/6 months of installation.Corten maturation 2


Appearance/shades of the product at the end of the period of oxidation after about 12/18 months of installation.Corten maturation 3


Corten steel with special treatment metalco “Anti-washout”
corten-antidilavamentoNote: the reproduction of the shades shown on paper is only indicative. Upon request, platelet samples can be provided.


You can repair minor surface defects (smears, dents, stains). If the corten is natural/raw (without Antiwashout), rub down the surface with a piece of steel wool ( like Scotch Brite) on the surface, to eliminate the defect. Then, moisten with water and place the product on the outside, until the part returns to the surface characteristics of the rest of the piece.

If the corten is treated with Anti-washout, repeat the previous step, by first removing the treatment left with steel wool (e.g. Scotch Brite). After the area has re-oxidized after exposure to the environment, re-apply with a brush two coats of Anti-washout treatment (purchased from Metalco). If the Anti-washout degrades over time, due to weather or mechanical agents, it is possible to renew the treatment according to the procedure described above (removing residues – oxidation – applying treatment).

After complete maturation (average 12/18 months), corten is considered stable and you can suspend the application of Anti-washout treatment, unless you want to use it in order to revive the surface, making it more shiny and smooth.

In case of any doubt about the proper maintenance procedure, please contact the Metalco Quality Department for advice.