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
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.