Corten steel in contact with other materials The design of exterior wall cladding in Corten steel requires special attention. Limeparts takes this into account in the design of its exterior walls: materials that are below the exterior wall such as plaster, sandstone, bricks, natural stone, … can be discoloured by water that runs off of the Corten steel cassettes. This water contains dirt and oxides that can cause a brown discolouration. We never use Corten steel in the vicinity of the sea. swimming pools and next to public roads because the presence of chlorine salts causes abnormal oxidation.
Characteristics of Corten steel
Corten steel is steel to which a relatively large amount of copper has been added and relatively small amounts of other materials (including nickel Ni, chromium Cr and phosphorus P).
This results in a great increase in corrosion resistance in the untreated state, and in an increase in tensile strength.
The corrosion resistance increases because the copper causes a dense, stable layer of oxide to form after a period of time that protects the underlying metal quite well. With regular steel the oxide layer is not dense and the oxidation process continues without decreasing!
With Corten steel we must take into account that there will be a reduction in the thickness of the material
(because of the corrosion described above) of maximum 0.4 mm during the first 10 years and after that of
0.2 mm per 10 years. This phenomenon is called reduction and can be greater if free chlorides are present
on the surface. These can originate from sea salt, chlorine from swimming pools, de-icing salt, …
Visually, the following is obtained:
Immediately after placement, the cassettes have a metal colour.
Very quickly, under the influence of the wet and dry cycle, a light-coloured oxide layer will form that is very irregular. Discontinuities in the exterior wall (windows, doors, awnings, …) result in a disruption of the water flow over the exterior wall and will cause great differences in the discolouration of the surface.
After a few months, the surface will have a light brown colour (unless absolutely no water runs down the
This light brown colour will get its final dark brown colour after from 3 to 10 years.
The surface of Corten steel is continually in transformation. In this transformation, time plays an important
role. We also refer to the fact that upon damage to the exterior wall or if there are extensions or adaptations, there will always be a difference in colour between the old and the new. These colour differences decrease after a period of time.