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Metal Works

If someone offered you pre-rotted timber for your building, they would be given short shrift.

But when it comes to Cor-Ten, or weathering steel, we're selling broken biscuits, damaged goods, seconds.

The reaction of the man on the Clapham Omnibus is 'cor-blimey, guv'nor, you was sold a pup an' no mistake'. Quite why Dick Van Dyke travels on the Clapham Omnibus, I don't know, but within the design fraternity there is a different set of opinions. The appeal of something that decays in a predictable and graceful fashion is hard to deny, and the fact that the material needs no other treatment than a care in detailing is the sort of practicality of which Ozymandias would approve.

Cor-Ten was originally produced in 1930s America for railway coal wagons.

Some time later its suitability for civil-engineering structures was explored; buildings soon followed.Most architects of my generation will have been shown the Saarinen John Deere headquarters building at some point. I suspect a few of us will have used Cor-Ten in student projects or competitions. The problems occur when the real world brings real clients and planners, rather than compliant figments.

Next to the man on the Clapham Omnibus sits the typical client, who says:

'You're not sticking a rusty box on my Grade II*-listed church.' A mortgage provider adds: 'We would need to be assured of the longevity of the product.'

And an insurer pipes up: 'Can you guarantee at least 100 years' design life?'

Rust has an image problem. It is steel rot, after all. So let's accentuate the positive: it is a great colour.Designers love the stuff. It is a self-finished material and in that context it falls into the same group as timber and masonry - and self-finishes or natural finishes are inherently honest, aren't they? No nasty duplicitous paint or morally objectionable powder coating.Weathering steel - what you see is what you get, for years.

Cor-Ten is lying to us, you see. The rust layer is tough and impermeable, and behind it lies metal as genetically manipulated as any super-bug. This stuff is as resistant to water as MRSA is to antibiotics. If only old Ozymandias had built in weathering steel: look on my works ye mighty and despair

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