The Monument, London
Built of Portland Stone and topped with a flaming orb of gilded gold leaf, the Monument was built by architect Christopher Wren (of St. Paul’s Cathedral fame) in the 1670s to commemorate the rebuilding of London after the Great Fire in 1666.
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Although the simplistic name may not have involved too much pre-thought from its architect (or King Charles II, who commissioned it), the Monument was built with precision. It’s exactly 202’ tall (61.5m), or the distance between it and the site in Pudding Lane in the City – London’s historical core – where the fire started. But precision wasn’t only in recognition of the fire; The 15’ (4.5m) diameter fluted Doric-column design was also intended to be a scientific instrument with its height being used to carry out pendulum and gravity experiments, and a zenith observatory to track the movement of the stars.
But for all its precision when built, the column showed its age badly at the beginning of the 21st century.
Since its completion, the Monument underwent repairs and redecorations approximately once every 100 years. It underwent a complete renovation, which included re-gilding the copper orb, in May 1834; although damage from World War II bombs was repaired some 50 years ago, the last major restoration was in 1888.
In the intervening 120 years, weather erosion and pollution damaged and discolored the stone, and graffiti had been daubed on the walls of the viewing platform. The 18-month restoration project, begun in 2007, involved the cleaning and repair of the stonework, re-gilding of the golden orb, and addition of a modified viewing cage and specialist lighting. Cathedral Works Organisation (CWO) of Chichester, England, received approval as stone contractor – and soon found that the modern renovation entailed some truly monumental action.
A pre-renovation survey revealed that the column had moved slightly over the years, although it is still only 8” (203mm) out of plumb from the base of the 21’ (6.4m) square by 40’(12m) high pedestal to the top of the column. And, it moves seasonally by slightly less than a quarter-inch (6mm).
Erecting a scaffold round the Monument to its full height required some engineering to take into account turbulent local wind conditions (caused mainly by the surrounding tall buildings) of up to 150 mph. To reduce wind resistance, the scaffolding was boarded only on every third lift, and the boards were moved as work progressed.
CWO cleaned the external stonework in phases, firstly using the DOFF steam-cleaning system, and then the Jos Torc low-pressure vortex process. A biocide cleaning system also removed surface coatings, oil, and grease.
There was talk of using a laser cleaning system, but Bernard Burns, CWO managing director, says it wasn’t necessary.
“It’s not about what you use; it’s about the skill you have to use it,” he says.
What amazed his masons was the size of some of the Portland blocks in the column. “Some of them must weigh 3.5 tons,” Burns notes. “Possibly more.”
Internally, the removal of the structure’s windows had led to a lot of condensation that had left its mark on steps and walls. They were cleaned with water and stiff brushes, and windows have been reinstalled that, with regular opening and closing, should avoid future problems of condensation.
Graffiti was removed using specialist techniques.
CWO carried out repairs to the column using carefully selected Portland stone. Cementitious mortar used in previous repairs and repointing was removed and replaced with lime mortars.
On the abacus of the column is the viewing platform, where breathless visitors arrive after climbing the cantilevered spiral staircase. This platform used to be covered in asphalt; however, when this was removed, six huge slabs of Pooil Vaaish carboniferous limestone were revealed. This is the same black stone used on the staircase steps and was the original material used by Wren.
Pooil Vaaish comes from the Isle of Man, an island equidistant from Ireland and England, where it is known as Manx Marble. It’s not an easy stone to work; dense but brittle, it only occurs naturally in thin beds, leading to a high wastage factor to achieve the sizes of stones required for the replacement treads for 311 steps.
The treads were cut at CWO’s workshops in Chichester, and then honed on-site to give a smooth marble-like appearance and the correct slip resistance. As for the slabs on the viewing platform, CWO repaired the stone in-situ.
The new viewing platform, designed by Julian Harrap Architects of London, is a vast improvement on the 1950s cage it replaces for the Grade I-listed structure (a designation akin to U.S. historic-place registration). That cage had replaced a century-plus-old iron enclosure built after August 1842 when Jane Cooper, a servant girl, became the last of the structure’s six suicide leapers.
“We gave ourselves a brief to return to a balustrade similar to the 17th-century original,” says project architect Judy Allen. “This has been designed with a lightweight stainless-steel mesh which is practically invisible from the ground, but encases the area to stop people throwing themselves or debris from this height.”
The underside of the platform originally featured four ornately carved Portland limestone paterae, one for each spandrel below the walkway. These were individual pieces of stone secured by leaded wrought-iron hangers.
The last recorded mention of them is their removal on safety grounds in the early 20th century after a large section fell off and narrowly missed a person below. No record exists of their exact appearance, but references to literature and others of the time, including those on St. Paul’s Cathedral, informed the design.
Working closely with the architects, CWO’s carver masons sculpted the four paterae. They are deeply undercut, and tool marks have been left in the stone to enhance the shadowing. The result gives life to the carvings, and makes them more visible.
“Before we put them up I thought: No one’s going to see them under there,” Allen says. “But you can see them, and they really are great.”
With each stone weighing 551 lbs (250kg), suspending the paterae presented a major challenge. The solution was to hang them from bolts secured into the stonework with a specially formulated two-part epoxy resin. This still left the difficulty of fixing them to the underside of the spandrel; it was impossible to lift from above, and the nature of the carving left it vulnerable to damage if pressure was applied from below.
The answer 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 custom-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 and reveal the paterae as a complete stone.
Another element of the project was the repair of a 1674 emblematic bas relief by Danish sculptor Caius Gabriel Cibber on the Monument’s pedestal. It depicts the destruction of the City, with King Charles II and his brother James (then the Duke of York, later James II) giving directions for the city’s rebuilding, surrounded by Liberty, Architecture and Science as attendants.
“Being at a lower level and of such importance, it was decided that repairs should be carried out in lime mortar rather than cutting out and indenting with new stone,” says CWO’s Burns. “New stone was used only to replace earlier cementitious repairs.
“As a result, this work on the Cibber relief is designed to last just 15 years, whereas the work on the rest of the structure should mean it doesn’t need further attention for at least 80 years.”
On each of the four corners of the pedestal sits a dragon. They all required cleaning to remove algae and lichen growth; fractures were stabilized by the use of fine stainless-steel dowels, while missing stone pieces were modeled and carved on site.
At the structure’s highest point sits the golden orb representing the flames of the Great Fire. This needed specialized cleaning of the ovolo molding. Missing copper leaves, flowers, dragon’s ears and flames were replicated; the orb was then painted, sized and re-gilded with two layers of 23.5 carat gold leaf.
Unable to remove the orb, the gold leaf work was carried out in-situ – quite a challenge in the strong winds at the top of the structure. Some 23,750 sheets of gold leaf were hand-applied to an area of 1,130 ft² (105 m²).
The stone drum on which the orb sits also needed strengthening (it had started to lean), while other specialist teams repaired the 300-year-old staircase handrail and installed a new solid-oak door, bronze windows and atmospheric lighting
The crews also set up a panoramic camera system on the viewing platform, relaying images to a screen in the ground-level entrance lobby and the Internet. The latter will allow those visitors who cannot, or dare not, attempt the hard climb up the inside of the column to enjoy a bird’s eye view of London.
Client: City of London Corporation
Stone Contractor: Cathedral Works Organisation, Chichester, England
Architect: Julian Harrap Architects, London
Quantity Surveyor: Davis Langdon LLP, London
Engineer: Hockley & Dawson Consulting Engineers Ltd., Cranleigh, England
Claire Santry is a freelance writer covering the stone trade in the United Kingdom.
©2010, Western Business Media Inc.