Beverley Minster Settles on CMS Pozaments Heritage Grout
Heritage Grout from Tarmac CMS Pozament has played an important role in a project to halt structural movement in the Norman nave at Beverley Minster in East Yorkshire. Regarded as one of the most beautiful Gothic buildings in Europe, Beverley Minster was built mainly during the 13th and 14th centuries on a site originally founded as an 8th century monastery.
Minster surveyor Ross Allenby said: "Measurements of vaulting in the nave roof indicated that there has been about 150mm of movement over the 700 year life of that part of the building. We have taken measurements over the last 10 to 12 years and the movement has continued."
Tests showed that where foundations had been extended in the 14th century for the flying buttresses, they were set on loose blocks of chalk with no mortar and many voids. It was determined that movement was the result of the degrading of the small points of contact between the block chalk fill. Any slight movement under the toe of a buttress is amplified at roof level 15 metres above.
Specialist ground engineering contractors Fondedile Foundations Ltd, part of Systems Geotechnique, were contracted to stabilise the foundations under five flying buttresses on the north side of the Minster and eight on the south side. The Fondedile team, who carried out similar work on the Tower of London and Ely Cathedral, used controlled low-pressure injection techniques to consolidate the foundations, using Heritage Grout 1.5, a specially formulated low strength lime-based grout, from specialist grout manufacturers Tarmac CMS Pozament. The grout is designed as a void-filler for historic structures where low strengths and the absence of Portland Cement hydrates are desirable.
14 tonnes of grout was successfully injected, reaching a strength of 1.5 N/mm2 after a period of 28 days. The grout developed sufficient strength to consolidate the chalk, yet was weak enough to facilitate any future archaeological excavation of burial grounds that lie beneath.
Mr Allenby commented: "Visual inspections indicate that the grouting has achieved the planned level of penetration, but it will only be after months and years of roof level measurements that we can be certain the buttress footings are now stable."
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