NSS revisits the Chapter House of Westminster Abbey to see the completed project that we featured this time last year while the work was being undertaken by Nimbus Conservation of Frome in Somerset. This was the first time since George Gilbert Scott practically rebuilt the outer skin of the building in 1870 that it had received so much attention. The restoration work, led and funded by English Heritage who care for the Chapter House on behalf of the nation, predominantly used limestone from Chicksgrove Quarry in Tisbury, Wiltshire, with Perryfield Whitbed Portland for a gargoyle replacement and other limestones for indents. Nearly 40tonnes of replacement stone went into Nimbus’ £4million-worth of work, some of it as 32 new heads modelled, as tradition dictates, on the people involved in the project, including some of the masons who carried out the work.

It is a testament to the Chilmark stone and the design of George Gilbert Scott in re-cladding the medieval Chapter House at Westminster Abbey 140 years ago that the restoration work completed by Frome firm Nimbus Conservation this year needed less replacement stone than had been expected.

There were still 40tonnes of new stone used in the project, most of it from Chicksgrove Quarry in Tisbury, but once the scaffolding had been erected and close inspection was possible it became clear that more of the original fabric than had been anticipated could be preserved, albeit with some lime mortar repairs and stone indents.

Perryfield Portland limestone was used for the replacement of one gargoyle because of the large size of block needed and because another had been replaced using Portland stone at some point over the years, so there was a precedent for its use. A small amount of Derbyshire Fossil stone, Ogwell and Plymouth Grey from Devon, and Purbeck Downsvein from Dorset were also used for inserts.

The gargoyles are no longer used to shed water, which is collected in the lead-lined parapet gutters to drain down lead pipes with cast iron hopper heads (all of which were restored), so the redundant rainwater channels were used to house Cintec socks with bespoke stainless steel box sections bolted to them in polyester resin to reinforce the projecting stonework.

It was decided to provide this reinforcement because a number of structural cracks had been seen on the sides of the attached buttresses directly behind the gargoyles, which appeared to have been caused by the weight of the overhanging stone of the gargoyles.

Most comment and delight has been created by the 32 replacement carved heads. Rather than try to reproduce those that were there, Nimbus have followed the tradition of Scott’s masons in modelling the heads on people involved in the project. In Nimbus’ case that includes those from the Abbey, English Heritage, the architects and the contractors.

An extensive clean has also been undertaken. There was ivy covering the flying buttresses which first had to be removed. At high levels it had grown into the stonework, which had to be dismantled in order to extricate the growth.

Flaking and blistering surfaces were removed across the whole building using hand tools and the Chilmark stone was cleaned using a steam cleaner with an Aquila hot box from Tensid.

There were areas of thick sulphation that were reduced using rifflers, tungsten chisels and micro drill bits before being cleaned using a timed nebulous spray. In some areas ammonium carbonate poultices were applied to stubborn areas of sulphation. All the masonry was sprayed with a biocide to prevent vegetation growth.

Repointing used hydraulic lime mortars and a lime shelter coat was applied in two layers to the floral panelling, drip moulding and stiff leaf carvings, and on the repaired gargoyles.

There was a lot of work and the deadline was immovable because of the Queen’s visit to see the finished work on 21 May. At times there were as many as 40 people working on the scaffolding at once to ensure that the project did hit the deadline. “It was all about good communication,” says Site Manager Angus Lawrence.