1 April 2006 - BEVERLEY MINSTER SETTLES ON CMS POZAMENTS HERITAGE GROUT
Beverley Minster in East Yorkshire is one of the great churches of England. It was built mainly during the 13th and 14th centuries on a site originally founded as a monastery early in the 8th century. The magnificent church, widely regarded as one of the most beautiful Gothic buildings in Europe, has splendid external decoration, rich with sculptures and intricately carved detail. The impressive 14th century nave and beautiful 15th century east window, that still contains much of the original medieval stained glass, dominate its spectacular interior.
PToday, following major restoration work during the 18th and 19th centuries, work to preserve the fabric of the structure still continues. One such scheme, carried out under the supervision of the Minster's architects, Carden & Godfrey, involved the stabilisation of foundations to halt a continuing problem of movement in the Nave.
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, although it is only a few millimetres, we have to look ahead to the next few hundred years and ask if there will be a problem then."
The Minster Old Fund, which is the trust responsible for maintaining the fabric of the building, appointed consulting engineers Price Myers to determine how and where the movement has occurred. A series of test bores and small excavations were made to ascertain the nature of the Minster's foundations and the land on which is it is built.
Mr Allenby explains: "Tests showed the basic foundations to be sound, but where foundations had been extended for the flying buttresses of the present building, in the 14th century, 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, even if it is still only measurable in fractions of a millimetre".
To reduce or halt further movement, the Minster Old Fund contracted specialist ground engineering contractors Fondedile Foundations Ltd, part of Systems Geotechnique, 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 blocky chalk foundations.
Heritage Grout 1.5, a specially formulated low strength lime-based grout, from specialist grout manufacturers Tarmac CMS Pozament, was selected. 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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Bryan Smith at Tarmac CMS Pozament. Tel: 01283 554800.
