On 16 February the restoration of The Monument in the City of London came to an end and the public were able once again to climb the 311 steps going up the inside of The Monument with their new Pooil Vaaish limestone tread inserts to the viewing platform redesigned by Julian Harrap Architects. NSS led the way. A website set up to track the restoration work being carried out by stone and conservation specialists Cathedral Works Organisation (Chichester) Ltd on The Monument in London has had more than a million hits. The Monument is the Portland limestone monolith topped by a gilded ‘burning’ orb erected to commemorate the rebuilding of the City of London following the Great Fire of 1666.

After 18 months of being wrapped in scaffolding receiving the attention of stone and conservation specialists Cathedral Works Organisation and the various other specialists working for them, The Monument in London has re-opened to the public. On 16 February the new £12,000 oak doors were opened to admit the first of the 100,000 visitors expected this year. They will climb the 311 Pooil Vaaish limestone steps to the viewing platform in the same stone to look out over the City and along the Thames to Tower Bridge and beyond.

At 202ft tall (61.5m) The Monument is sometimes said to be the world’s tallest free-standing stone column, but it depends how you define a column. The Washington Monument, commemorating George Washington in Washington, USA, was finished in 1884 at 555ft 5 ¹⁄₈in (169.3m) tall, but it is an obelisk. A few other self-supporting stone (or stone clad) columns that are taller than The Monument have since been built and lay claim to being the tallest in the world.

Tallest or not, the monolithic Portland limestone Monument in London is impressive. It is a Grade I listed Scheduled Ancient Monument. It was built between 1671 and 1677 by Sir Christopher Wren and Dr Robert Hook to commemorate the rebuilding of the City after the Great Fire of 1666 (hence the ‘flaming orb’ on the top that was regilded during the current phase of work for the first time since 1834).

Julian Harrap Architects worked on the £4.5million restoration for the clients, the City of London Corporation. Project architect Judy Allen told NSS that although the practice specialises in conservation work on important listed buildings, it was still a privilege to have been involved with The Monument.

Bernard Burns, the Managing Director of Cathedral Works Organisation (CWO), (pictured left on top of The Monument behind the newly re-gilded orb) says his company gained the project as main contractors as a result of their award-winning work returning Wren’s Portland limestone Temple Bar, one of the 17^th century gates of the City, to London in 2004. “I was able to offer the City essentially the same team that did Temple Bar,” he says.

The Monument was built with precision – it is 202ft (61.5m) tall because that is the distance between it and the site in Pudding Lane where the fire started. But the precision is not only in recognition of the fire. The 15ft (4.5m) diameter fluted Doric column was also intended to be a scientific instrument. It was built accurately so that its height could be used to carry out pendulum and gravity experiments. It is also a zenith observatory in its own right, with an 800mm view up through the middle of it from the basement and out through doors in the top of the orb to track the movement of individual stars. And all 311 steps are precisely 6in (152.4mm) high so they can be used as a scale in barometric pressure studies.

A survey before the restoration work started revealed that the column has moved slightly over the years, although it is still only 8in (203mm) out of plumb from the base of the 21ft (6.4m) square by 40ft (12m) high pedestal to the top of the column standing on it. And it moves seasonally by 6mm. Studs put on the walls to carry out the survey have been left in place to enable future plumb surveys to be undertaken.

Erecting a 70m high scaffold round the Monument required some careful consideration and engineer Jack Jenner was contracted to design it. He had to take into account the turbulent wind conditions resulting from the surrounding buildings. The scaffolding had to be able to survive wind gusts of 150mph and to help it do that without becoming too massive, screening covered only the lower 25m. It was also boarded only every third lift to try to keep the size and weight (not to mention the cost) down. The boards were moved with the work.

Even so, the scaffolding required what were effectively above ground foundations and still cost £400,000.

The first job was to clean the stonework. The architects did not want the stone brought up as new because they wanted to retain some of the character of age and specified an 80% clean. CWO started by using the Doff steam cleaning system then the Jos Torc low pressure vortex process. A biocide was also used where necessary to remove surface coatings, oil, and grease. There was talk of using laser cleaning, but Bernard Burns says it was not necessary. “It’s not about what you use, it’s about the skill you have to use it.”

What amazed the masons was the size of some of the Portland blocks in the column. “Some of them must weigh 3-3.5tonnes. Possibly even more,” says Bernard.

Internally, the lack of glazing in the slit windows had led to a lot of condensation that had left its mark on the steps and walls. They were cleaned with water and stiff brushes and bronze windows have now been installed, which, with a programme of opening and closing, should avoid the worst of the condensation in the future. Graffiti was removed using specialist removal techniques and it is hoped surveillance cameras and loudspeakers on the viewing platform that are part of £350,000 worth of new electronics will prevent future attacks at high level.

CWO carried out repairs to the column using carefully selected Jordans Whitbed Portland stone supplied by quarry company Albion. Where cementitious mortar had been used for previous repointing it was removed and replaced with lime mortars.

On the abacus of the column is the viewing platform that is open to those members of the public willing to climb the steps of the cantilevered spiral staircase – all 311 steps of which have new Pooil Vaaish tread inserts. The platform encompasses a moulded cylinder that supports the flaming golden orb.

The surface of the viewing platform was covered in asphalt. Lifting it revealed six huge slabs of the same Pooil Vaaish carboniferous limestone as the steps. Pooil Vaaish comes from the Isle of Man, where it is known as Manx Marble, and has been identified as the material used originally by Wren. Some replacement and repair was required.

Working with Pooil Vaaish proved to be a challenge in itself for CWO. It is dense but brittle and occurs in thin beds, which meant there was a high wastage factor.

CWO made several trips to inspect the stone in the quarry and monitor its extraction. One load was stranded in the coastal quarry for several days by high seas. Adam Stone, CWO’s Technical Director, praises the suppliers. “Great effort was made by the people at Pooil Vaaish to ensure sufficient supply,” he says.

Julian Harrap Architects’ new viewing platform is a vast improvement on the 1950s cage of iron bars it replaces. The first ‘cage’ was put around the platform in the 19^th century after a sixth suicide. It was replaced in the 1950s by more iron bars. Judy Allen says this time the brief the architects gave themselves was to return to a balustrade similar to the 17^th century original with a light-weight stainless steel mesh practically invisible from the ground encasing the area to stop people throwing both themselves and debris off.

The underside of the platform had originally been decorated with four Portland limestone paterae, one for each spandrel below the walkway. They were individual pieces of stone secured by leaded wrought iron hangers. The last recorded mention of them is their removal on safety grounds more than 100 years ago after a large section fell off and crashed through an office window, narrowly missing a worker. A mason was lowered on a rope to remove them.

There is no record of what they actually looked like, but reference to literature and other surviving paterae from that time, including those on Wren’s St Paul’s Cathedral, informed the design of the new ones.

Working closely with the architects, CWO’s carver masons sculpted the four stones, first producing scale models made of modelling compound for approval. They are deeply undercut and tool marks have been left in the stone as worked to enhance the shadowing and give life to the carvings, making them more visible from the ground.

Judy Allen says: “Before we put them up I thought: no-one’s going to see them under there. But you can see them and they really are great.”

With each stone weighing 250kg, suspending the paterae was one of the big challenges for structural engineer Clive Dawson, whose solution was to hang them from bolts secured into the stonework above with a specially formulated two part epoxy resin.

This still left the challenge of fixing them to the underside of the spandrel when it was impossible to lift them from above and the nature of the carving left it vulnerable to damage if pressure was applied from below.

The solution was to lay the stones face down on a cushion, with a hole in the middle to allow the location of the central pin of the hanger. The cushion was placed on a purpose made cradle and jacked into place using a genie lift with fork extensions, enabling the mast to clear the viewing platform. Large circular plates were fixed and bolted to the central pins, over which a carved centre piece was inserted to mask the fixing.

The entrance to The Monument in the pedestal has been given a new Purbeck limestone floor, with stone supplied by quarry company WJ Haysom & Son and Landers Quarry. Victorian turnstiles have also been added to restrict entrance to 40 people at a time because they all have to climb up and descend the same flight of stairs and get out on to the viewing platform.

On the west side of the pedestal is a museum grade emblematic sculpture in alto and bas relief by Danish sculptor Caius Gabriel Cibber, a prominent stonemason sculptor of Wren’s time.

Being at lower level and of such importance it was decided that in order to preserve as much of the original material as possible most repairs should be carried out in lime mortar rather than cutting out and indenting with new stone. New stone was used to replace earlier cementitious repairs only.

Consequently, the work on the Cibber relief is designed to last just 15 years, whereas the work on the rest of the structure should mean that the column does not need further attention for another 80 years at least.

The Cibber relief depicts the destruction of the City, with Charles II, the King at the time, and his brother James, the Duke of York, surrounded by Liberty, Architecture, and Science, giving directions for the city’s reconstruction. The other three sides of the pedestal are lettered with Latin text relating to the fire and the rebuilding.

On each of the four corners of the top of the pedestal sits a Portland stone dragon, the work of Edward Pierce Junior, a sculptor and architect frequently employed by Wren.

The dragons required cleaning to remove algae and lichen growth and had suffered bomb damage in World War II. Masonry of the column itself that had bomb damage was not repaired because it was considered part of the historical evidence of the building. However, there were missing pieces of wings, ears, tongues and tails of the dragons that it was decided to replace with lime mortar repairs in order to restore the profile. It was decided to repair the carvings with lime rather than replacement stone so that the repair would be clear and easily reversible if anyone ever wants to reverse it.

There were also fractures that were repaired by using fine, stainless steel dowels, a technique used to retain as much of the original stonework as possible.

Between the dragons are four stone sculptures, one on each face. They include the City coat of arms and its charter. These were also cleaned and restored by CWO.

The gilded copper orb at the top had to be restored in situ. It is made of 4mm copper sheets. Nobody knew exactly how much it weighed, but they didn’t want to find out.

It required specialist cleaning and replacement of missing leaves, flowers and flames, work carried out by Rupert Harris Conservation. The orb was painted, sized and re-gilded with two layers of 23.5carat gold leaf by Hare & Humphreys.

Gold leafing the orb at the top of The Monument, where wind gusts of 90mph had been recorded, even with windbreaks erected, “presents it own challenges”, says Bernie Burns. The double layer gilding took 23,750 sheets of gold leaf to cover an area of approximately of 105m².

The orb is fixed to the stone dome below it by a wrought iron frame with four legs. But one of the legs was longer than the others and gradually the stone below had been compressed on one side and opened up on the other, compounded by the rusting of consequently exposed iron cramps. This was corrected and three new iron bands were inserted to hold the orb in place. The iron cramps in the stone were replaced with stainless steel cramps.