The advantages of Patina in different conditions
Thanks to their patina layer, weathering steels can be used in outdoor structures without any separate surface treatment. At its best, weathering steel can save the costs of all the surface treatment and the repairs necessary later. The cost advantage in comparison to painted structures is emphasised in environments where regular repainting is required. The Rust Brown method extends the architectural use of weathering steels in indoor structures. It is recommended to make all markings in all applications during construction using chalk or water soluble colours.
Open air structures and patina
Weather resistance is based on the oxide layer, i.e. patina, which as a result of the alloying elements is dense and nearly impervious to oxygen. Under normal weather conditions the patina will form in about 18 - 36 months, if the surface is alternately wet and dry. At first, the patina is a reddish brown colour, but with time takes on a darker hue. In industrial environments, the patina forms more quickly and is darker in colour than in rural areas. In marine environments, the formation of the protective patina may be slower due to chloride exposure. For open air structures, the slow corrosion rate is taken into account of by adding corrosion allowance to the nominal thickness, see table above.