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Underpinning set to become a thing of the past

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A SIMPLE, cheap and non-disruptive masonry reinforcement technique that could eliminate the need for underpinning except in the worst cases of subsidence has been endorsed by universities in England and Germany.

Bath University Centre of Window and Cladding Technology director Stephen Ledbetter said the reinforcement technique was a better option than underpinning for most types of masonry structures, ranging from historic buildings to private housing.

'Building owners rarely notice the ground movement that causes the problem - it's the resultant cracking that concerns them,' he said. 'Adding just a small amount of reinforcement to the vulnerable areas of the wall makes them more elastic and resistant to shear and stops further crack development.'

Researchers at Bath, backed by work at Karlsruhe University, assessed a commercial masonry reinforcement system based on a resin grout and reinforcement with standard stainless steel rebars grouted into position in slots cut into the mortar joints. Both techniques proved capable of coping with extra ground movement up to double that which would have caused the original cracking.

The results were assessed in the light of long term monitoring of the settlement-damaged facades of Georgian terraces in Bath and a 1960's apartment block in Grangemouth, Scotland. Ledbetter said the technique was particularly suitable for historic buildings as it was largely non-invasive.

He added: 'For domestic properties, provided there isn't a major landslip, reinforcement should be significantly cheaper and a lot less disruptive than traditional underpinning. The only real problem is that house insurers seem to prefer rigid foundations to a flexible house.'

More information is available in Masonry crack damage: its origin, diagnosis, philosophy and a basis for repair, by Cook, Ledbetter, Ring and Wenzel on www.ice.org.uk

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