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Monumental effort to move Temple Bar

SITE REPORT

After spending 125 years in the wilderness - well, Hertfordshire - Christopher Wren's Temple Bar is coming home to London, to its new resting place in Paternoster Square. Joanna Booth reports

LONDON'S Temple Bar, an arch of Portland stone with an ornate gatehouse on top, stood at the end of Fleet Street for 200 years before it retired to the country.The process of bringing it back to the city has been much more complicated.

'In 1878 it only took them 11 days to take it down, ' says Gary Collings, site manager with the Cathedral Works Organisation, the main contractor on the project.'It's taking us 72 weeks to put it back up.

'But you should see the pictures of how they went about it! They were hacking it with pick axes and throwing blocks of stone down on to the ground.'

A stonemason for 30 years, Mr Collings has worked on countless restoration jobs. But even he describes this project as unique.

'I've never taken a building down and rebuilt it again from scratch, ' he says.'This has been very enjoyable, but it's also very worrying.'

There's certainly no lack of care in the methods employed by the specialist stonework company.

Under the watchful eyes of its own consultant conservator, Deborah Carthy, and English Heritage personnel, the process has been designed to cause as little damage to the stones as possible.

CWO got a nasty shock when its workers began dismantling the Bar in the gardens of stately home Theobalds Park in Hertfordshire.Operational director Bernard Burns explains: 'The outside was mainly pointed in lime.

But then we got into the main section of the building and found that everything was literally glued together with cement mortar.The Victorians had just discovered what it could do, and it was everywhere.'

Mr Burns is sceptical as to whether the Bar would have been moved at all if surveys had discovered the cement.

He says: 'It's a Grade I listed building and a scheduled ancient monument. I don't know of any other scheduled ancient monuments that have been moved at all, let alone when they've been covered in cement mortar.'

The whole job had to be rescheduled to give the company time to painstakingly remove the cement as gently as possible. Small breakers were used to take out 80 tonnes of concrete rubble from the core over the arches but, other than that, English Heritage would allow no percussion tools near the structure.

'Every single stone had to be prised away by hand, 'Mr Burns recalls.

And this wasn't the end of the problem.Mr Burns adds: 'The architect describes the way the Bar was rebuilt in Theobalds Park as a theatre set.

They threw it up very quickly. It wasn't plumb or level when we found it - not because of settlement but due to the fact they put it up any old how.'

Some of the stones had been lost and some skewed round so that the mouldings were on the inside.

The roof of the structure rotted off at least 40 years ago and the water damage was significant. CWO had to construct a scaffold system that allowed it to shroud the structure in monoflex and cover it with a temporary roof.A biocide was used to kill the algae coating the Portland stone and then it was cleaned. Reluctant to expose the stone with yet more moisture, the company decided to blast it with a calcium carbonate aggregate to remove the worst of the dirt. Each of the 2,700 stones were individually numbered and photographed before being stacked on to 500 pallets ready for the journey to Paternoster Square in London.

The Bar is being rebuilt as a gateway to the new Paternoster Square development neighbouring St Paul's Cathedral, barely 1 km from its original home on Fleet Street.The Bar is squeezed between two existing buildings - a mere 10 mm expansion joint on each side gives it space to breathe.

On a site this tight the stonework specialist faces a number of logistical challenges.The scaffolding had to incorporate transverse beams so hoists could be used to lift stones into position as there is no space for a crane.

'We are lifting with the same methods as the Victorians would have used, ' says Mr Collings.'Our block and tackle hoists are chain blocks, and our webbings are made of silk to protect the stone, but it's basically the same.'

CWO also uses a traditional device called a Lewis pin.A hole is drilled into the top of each stone and twin metal dowels braced inside the cavity so the stone can be lifted.

Unable to buttress the sides of the structure, CWO has incorporated a tensile stainless steel Macalloy bar connected to 40 mm-thick steel plates at either end to combat forces pushing the structure to buckle out at both sides.

This runs above the main arch, and had to be installed in four lengths, as the space between the buildings wouldn't allow the entire length to be fed through at once.

Mr Burns says: 'It's putting modern post-tensioning stonework technology into a traditional building.'

Because each block is slightly different, getting the structure plumb and level was a more complex task than simply lining up the stones.After taking setting-out points the contractor uses laser levels to get each block into the correct position.

CWO tried to avoid replacing stone wherever possible.Where a block was badly decayed, it was not replaced but cut back and remodelled.

'We've made very few additions of new stone, ' says Mr Collings.

'English Heritage is very reluctant to let us put any new stone in. Each new piece has to be approved.'

Work has just reached the top of the main arch, which is about half the 13 m height of the building.Above this, the cavity will be filled with a limestone mixture.All pointing is also done with lime, so that the building can breathe and further water damage be avoided.

Now CWO is beginning on the main room itself, and the four statues can be replaced.The statues were removed and left lying on their sides, putting stress on areas not designed to be load bearing. CWO's carvers had to repair noses and beards before they were ready to face the public once more.

'The arches were the most problematical part. Setting out was a real challenge, ' says Mr Collings.

'And the arches are very unstable until the keystone is put in. But now that part is completed I think the rest of the building will fly up, it will be much easier.'

Ultimately a slate roof will cap the structure, and a thin sacrificial limewash will be painted over the stone.Huge oak gates will be fitted across the main arch.

The project is scheduled for completion in early November.

'It has been an incredibly rewarding experience, ' says Mr Collings.'And we've had a lot of interest. People keep stopping us and asking what we're doing. But our biggest fans are a couple that used to come and see us when we were dismantling the structure in Hertfordshire.They now make a weekly trip down to London to check on our progress.'