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CORTEN steel and the Curious Case of the Fretwork Gate

Why Corten Steel? It seemed straightforward enough. All Metal Solutions (AMS) had been hired by property developer Dwyer Construction to supply certain steel elements in a prestigious housing development in St John’s Wood, London. The brief included railings, the entrance gate and a stand-alone planter, providing advice on suitable metals to make them and, oh yes, a weathered finish.

To meet the project architect’s request for the right finish, AMS recommended a specialist steel called Corten Steel. It contains chemicals that produce more resistance to atmospheric corrosion than other steels; over several years Corten steel reacts with the weather to produce a protective surface. But in this case, the architect did not wish to wait for the ‘weathered’ effect; he aimed to install it as a finished design feature from the start and in a specific colour and patina.

Search for a new look

Such a look had not been produced by AMS before – not only had the company to find new ways of handling and machining the steel but it also had to create a surface colour and a finish to order.

What made the task more complex was uncertainty about the physical properties of the box-section steel once it had been machined – a key factor in constructing the 2m high gate system. The design required the number ’10’ (part of the development’s postal address) and surrounding decorative steel fretwork be cut out of the gate’s central panels.

AMS opted to laser-cut the fretwork. It produced a prototype of the panel only to find its structural strength had been significantly weakened and would not make the gate secure or vandal-proof.

Going for that ‘weathered’ look with Corten Steel

corten steel weathered lookAdd to that the challenge of achieving the colour and ‘weathered’ look of the design, and AMS had to return to the drawing board. Umpteen prototypes later, as expected, it found that the panels with more material removed were structurally weaker. Despite this, the architect required a more open style and said no to ‘thicker’ fretwork panels.

How about mounting the fretwork on an aluminium backing sheet?” Piped up the research team. That  way, they argued, the gate could strengthened structurally but still incorporate the ‘lighter’ fretwork design.

Steel fretwork that had to adhere

Again, there was a snag: finding an adhesive strong enough to fix the thin and small areas of steel fretwork to the aluminium sheet without ‘bubbling’ and consequent weak adhesion. After several trials, they found a two-part epoxy adhesive to do the job.

AMS’s challenges were still not over. Creating the desired weathering effect was new territory and it took repeated experimentation before they hit on the idea of ‘pickling’ the steel in a corrosive bath of acetic acid and sodium chloride.

corten steel fretworkAgain, after considerable testing, the right combination of chemicals producing the desired colour was discovered. It ticked all the boxes: safe to use, thoroughly tested, did not damage the steel and produced a rust-like finish – just what the client ordered.

All Metal Solutions Limited (AMS) is an established and well-recognised fabrication business covering Hertfordshire and London for both new build and building maintenance. Based in Welwyn Garden City, AMS offers a highly skilled steel fabrication and site installation service for a wide range of products ranging from structural steelworks to architectural metalwork.

For more information or to arrange an initial consultation, please call: +44 (0) 1707 881177, or contact us via this link >>>