Caring for the stone of the UK’s most iconic temporal and spiritual buildings

The renovation of the Houses of Parliament, expected to cost at least £3.8billion, will be one of the biggest stone conservation projects ever – perhaps the biggest carried out as a single project – and certainly one of the most significant.

Before the end of this year, both houses of Parliament should have voted on how they want to proceed with a project to protect and renovate the building they work in, the Palace of Westminster. It will be perhaps the biggest and most significant conservation project ever undertaken, certainly in the UK.

The building housing the ‘Mother of Parliaments’ is recognised worldwide. The 1,100-room palace seen today mostly dates from the mid-1800s and is arguably the most important Gothic revivalist building in the world. The building it replaced was devastated by fire in 1834, although Westminster Hall, built in 1099, survived and is still in use today.

Each year the palace (and it remains a Royal Palace, even though it was designed to house Parliament) has more than a million visitors, including 100,000 school children. It is a Grade I listed building and, with Westminster Abbey and St Margaret’s Church, forms part of the UNESCO Westminster World Heritage Site.

A Joint Select Committee on the Palace of Westminster reported its recommendations for the renovation of the building in September after its year-long consideration of an independent options appraisal by Deloitte.

The option it favours is the full decant – vacating the premises to allow builders to get on with their work. It is the quickest and least expensive of the five Deloitte options at £3.8billion (although many believe that is only a starting figure).

Although the Houses of Lords and Commons are supposed to vote on the proposal by the end of this year, don’t start sharpening your chisels just yet. These are just the preliminaries. Nobody expects work to start before 2022 at the earliest. It could start a lot later. And it will go on for years.

As with many large old buildings, repair and maintenance of the Palace of Westminster is perennial. And when conservation and masonry skills are needed it has often been specialist DBR that has been called upon, whichever main contractor wins the work.

For the past eight years the company has worked there fairly constantly, and it was in and out for many years before that.

It has even been involved in the creation of a special Palace of Westminster Poultice by Restorative Techniques (click here for more about the latest developments from Restorative Technqiues). DBR trialled a variety of products from various producers and wrote a full report on the results before the Restorative Techniques product was chosen as the most suitable for successfully removing the stubborn soiling without damaging what can be a friable substrate.      

But it is only the most pressing jobs that have been carried out at the Palace of Westminster and the conservation of the building has been a losing battle against deterioration. The Victorian building also struggles to accommodate the facilities required by the modern world, especially communications networks, which the renovation of the building will address.

Stone and conservation companies have been as busy as everyone else since the uncertainty of the EU referendum, which had presumably been the reason for the generally subdued level of activity in the first half of this year, turned into the continuing uncertainty of Brexit, but which people seem to have decided to ignore in order to get on with their lives.

It is impossible to predict with any accuracy what level of activity there will be in the industry five years in the future, of course, but considering the heritage sector’s repeated claims of skills shortages, nobody seems to have considered the question of  availability of suitably qualified people, including stonemasons, to carry out the work proposed. Perhaps Parliament considers any skills deficit in the UK will be met by people from beyond the shores of these islands.

The choice of a sand-coloured limestone from an Anston Quarry in Yorkshire to rebuild the palace after the fire of 1834 has often been criticised. 

It was chosen after a tour of UK quarries and buildings in 1839 by a committee that included the architect Charles Barry, two leading geologists and a stone carver. Anston was chosen because it could be supplied in blocks up to four feet (1.2m) thick and lent itself to detailed carving. It might not be coincidental that it was also cheaper than alternatives being considered.

In coal-burning London, acid rain and carbon deposition took their toll and deterioration of the stone was noted as early as 1849. Barry experimented with applied treatments to the stone which he believed had halted the decay. They hadn’t.

By the 1920s Members of Parliament were being advised to sit on the River Thames side of the Members’ Terrace rather than near the walls of the building after a large piece of stone fell off Victoria Tower on to the Terrace.

Over the years, various stones have been used to carry out repairs to the building, including Harrycroft, Cadeby and Clipsham.

Some of it was not ideal, says Dr David Jefferson of Jefferson Consulting in Leicestershire. He says the introduction of Clipsham, a hard crystalline detrital limestone with low permeability, into a much more permeable secondary dolomitic limestone of lower compressive strength is potentially a recipe for disaster.

However, much of the Clipsham that was used went into the construction of extensions to the building in some of the courtyards, so has little contact with the original stonework.

Dr Jefferson has told NSS that the stone originally selected for the palace was magnesian limestone from Bolsover Moor. Unfortunately, the rate of extraction of acceptable stone of suitable bed height could not be maintained. Production was switched to Mansfield Woodhouse but, once again, it struggled to achieve the bed heights required.

By 1843 when the walls of the new building were some four to five metres high, the stone was being supplied from Anston (where there were 300 men recorded working in the quarry) supplemented by Caen stone from France.

This fulfilled the main criteria of acceptable bed heights in sufficient quantities to match the building schedule.

Dr Jefferson says problems encountered with the magnesian limestone are almost certainly a result of the high demand for the stone on the project. The geology of the Anston area is significant. Rather than a series of regular beds of magnesian limestone, the strata can consist of a number of patch reefs, or bioherms, separated by areas of variably bedded stone of varying bed heights that are petrographically variable. In addition, thin beds of marl are not uncommon, presenting as thin films within some of the limestone. Careful selection of the stone is therefore essential. But Dr Jefferson says it was not always achieved, “almost certainly due to the pressures placed on those employed in constructing the new building to finish the work as speedily as possible”.

He maintains that the majority of the stone was a perfectly good material for the construction of the palace (in spite of the level of pollution in London at that time and for many years afterwards) and that most of it has survived extremely well, as it has in other areas of the country where it has been used where pollution was also high, such as Mansfield and Doncaster.

While the centre of temporal administration in the UK plods on towards its renovation, the centre of pastoral administration, at least for the Anglican Church, has just had completed the latest phase of work in a constant battle against the ravages of time. Scaffolding that has hidden the Great South Window of Canterbury Cathedral since 2009 has been struck.

Although a little of the original stone and its later replacement has been reused (after cleaning), most of it has been replaced and the window is now essentially a 20^th century structure, albeit a faithful reproduction of the original 15^th century window. Heather Newton, Head of Conservation at Canterbury Cathedral, says there was enough stonework detail left to be able to know exactly what it originally looked like. The rest was down to the skill of the cathedral’s masons.

The window was completely removed and most of the stone has been auctioned off – you might have followed the story on this magazine’s website (click here for a report about the sale).

There were 144 lots, with bidders coming from as far away as America and India. Some pieces went for thousands of pounds and the sale raised a total of £210,000 that will go towards future restoration work.

It is a huge window – 25ft wide (7.6m) and 55ft (16.7m) from the cill to the inner arch of the apex. That there was a problem with it became apparent in 2009 when a significant piece of it fell away. Scaffolding was immediately erected both inside and out to support the window, which was bowing alarmingly, and to prevent pieces of stone from falling on people below or damaging the priceless stained glass in the window, which is older than the wndow itself having been taken from other windows in the Cathedral when the Great South Window was built.

The original glass is recorded as having been ordered in 1428 during the build of the transept in which the window sits. Today all that remains of that glass is high up on the window, the rest having had stones thrown through it by iconoclasts. Some of the glass at the top of the window survived because they could not reach it. The rest of the stained glass now in the window was taken from other parts of the cathedral, some of it dating back to the 12th century, and put into the Great South Window during an 18^th century rebuild.

That the window was rebuilt in the 18^th century is an indication that its problems are not new. Some of them are believed to have been exacerbated by a drain under the wall, which was leaking. It has now been mended and reinforced.

Repairs to the window over the centuries had seen stones replaced and repaired with a variety of other stones, including Portland. For the new work the stone used is Lavoux à Grain limestone that was supplied by Pierre de Paris. It is a good match for the original French limestone and was chosen because it has bed heights of more than 1m. That was necessary in order for the mullions to be able to replicate the original design in size so the joints in the new window match those of the original.

The stone was sawn six sides by the supplier to minimise the amount of waste transported, then sawn on a Gilbert wire saw that was bought by the Cathedral for this project to work alongside its Wells Wellcut at its masonry yard on the edge of Canterbury. Its 17 masons produced the individual pieces of the window using templates cut by the Cathedral’s draughtsman, Darren McCulloch-Smith, who did the setting out using old fashioned methods, including dropping plumb lines, because of the difficulty of access around the scaffolding and so that the eccentricities of the stonework could be accommodated in the new work. The new window has slightly better lines than the one it replaced, but only slightly because it was decided early on the stained glass was to be returned to the window and that drove the whole project.

As the window was dismantled the degree of damage the stonework had sustained became apparent. In several cases it had split down the middle and the gap was so wide you could see from one end to the other.

Head Mason Tony Long was in charge of rebuilding the window, with four masons at a time working on it. “Logistically it was difficult,” he says. He praises the masons on the bankers for the accuracy of their work but says when there were transom heads with 14 different joints to be fitted in using traditional poured lead joints, the language was occasionally inappropriate for a cathedral.