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Metal Effect

Occasionally, we take on projects that are quite unique.  Recently, a couple built their new home using weathered steel as their siding.  At first, I must admit I wasn’t sure I would like it.  But, after seeing the finished product, all I can say is “Wow!”  I was really impressed with how it turned out!

Originally designed as a steel that did not require paint to seal it from the weather Corten steel has become a popular option for aesthetic reasons in recent years.  The term “Corten” is short for the terms “corrosion resistance” and “tensile strength”.  The principle behind Corten steel is that the rusting process seals in and protects the base layer of steel beneath it.

Weathering steel, often referred to by the genericized trademark COR-TEN steel or “Corten” steel, is a group of steel alloys which were developed to eliminate the need for painting, and form a stable rust-like appearance after several years’ exposure to weather.

The surface oxidation of weathering steel can take six months, but surface treatments like using hydrogen peroxide and salt can accelerate the oxidation considerably.


In 1933 the United States Steel Corporation developed and patented a steel with exceptional mechanical resistance, primarily for use in railroad hopper cars, for the handling of heavy bulk loads including coal, metal ores, other mineral products and grain. The controlled corrosion for which this material is now best known was a welcome benefit discovered soon after, prompting USS to apply the trademarked name Cor-Ten. Because of its inherent toughness, this steel is still used extensively for bulk transport and storage containers.

Railroad passenger cars were also being built in Cor-Ten, albeit painted, by Pullman Standard for the Southern Pacific from 1936, continuing through commuter coaches for the Rock Island Line in 1949.


Weathering refers to the chemical composition of these steels, allowing them to exhibit increased resistance to atmospheric corrosion compared to other steels. This is because the steel forms a protective layer on its surface under the influence of the weather. The corrosion-retarding effect of the protective layer is produced by the distribution and concentration of alloying elements in it. The layer protecting the surface develops and regenerates continuously when subjected to the influence of the weather. In other words, the steel is allowed to rust in order to form the protective coating.


The first use of weathering steel for architectural applications was the John Deere World Headquarters in Moline, Illinois.  The building was designed by architect Eero Saarinen, and completed in 1964. The main buildings of Odense University, designed by Knud Holscher and Jørgen Vesterholt and built 1971–1976, are clad in weathering steel, earning them the nickname Rustenborg (Danish for “rusty fortress”).  In 1977, Robert Indiana created a Hebrew version of the Love Sculpture made from weathering steel using the four-letter word  (אהבה, “love” in Hebrew) for the Israel Museum Art Garden in Jerusalem, Israel. In Denmark, all masts for supporting the catenary on  are made of weathering steel for aesthetic reasons.

Rustic, Rural, Beautiful

A popular trend that has been occurring in mountain retreats, rural areas and ranch style homes, a Corten roof and siding offers a unique appeal to many homeowners.  In modern metal roofing applications, the trend tends to be using a weathering steel on a standing seam roofing panel.  In more rustic-styled designs, we see it used more with corrugated metal panels.

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