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Iron evidence

What's new? It seems that, as usual, 'aspiring' engineers have to learn afresh the lessons that are well known to their predecessors.

It is no secret among engineers and architects who specialise in historic structures that iron and steel embedded in damp external masonry has to be continually monitored. It may not be visible, but experience tells us where to watch out for symptoms of distress.

As long ago as 1932, the Department of Scientific & Industrial Research published Mr Schaffer's seminal work on 'the weathering of natural building stones' in which he noted that 'it is now so well known that iron cramps and dowels damage stonework that their use can be regarded as an error in craftsmanship'.

Such errors were even made by eminent architects. In the 1860s, George Gilbert Scott installed iron bars in the west tower of Ely Cathedral. We took them out in the 1970s and in conjunction with Purcell Miller Tritton and Professor Jacques Heyman, new stainless steel ties were introduced (see figure).

More recently at Westminster Abbey, the greatest restoration since the time of Wren has just drawn to a close, and £25M has been spent renewing stone decayed by pollution, and eliminating literally hundreds of embedded iron items.

Not all historical buildings have the luxury of such funding. For them, good maintenance, vigilance, and understanding are the keys to their future.

Clive Richardson (F), RT James & Partners, 19-21 Palace Street, London SW1E 5HS.

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