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Facing the future

HERITAGE ENGINEERING: St Pancras Waterpoint - Last November St Pancras Station's last surviving waterpoint was loaded on to transporters and moved to a new home. Dave Parker reports on its reconstruction.

Perched high on its embankment above the St Pancras Basin, the relocated St Pancras Waterpoint will look back on its past. Later this year, visitors climbing to the top storey of the rebuilt Grade II listed water tank will be able to take in a panorama which includes its original home at Kings Cross and St Pancras Stations to the south, and Hampstead Heath to the north. One day it will be a prominent milestone for passengers on high speed Eurostar trains on the CTRL line bound for the St Pancras terminus, which displaced it.

At the moment, however, work to remove the concrete ring beams that made it possible to relocate most of the 1870s structure in two sections is nearing completion (NCE 29 November 2001).

Stuart Armitage, project engineer for structural engineer the Morton Partnership, says the elaborate masonry survived the move without problems. 'There were some existing cracks, in the joints only, but these will be stitched with stainless steel plates.

'Our main priority now is getting the bottom storey faced up and carrying out repairs to old damage to brickwork on the upper storeys.'

The three sided ground floor structure had to be left behind at St Pancras but as many bricks as possible have been reclaimed to repair the damage. Most of the original brick flooring was too contaminated for re-use, says Armitage, although the stone door thresholds were salvageable.

Some of the limestone stringer courses will go into the new facings which will disguise the new brick core which now supports the two upper storeys.

And the heavily reinforced ground floor slab that spans between the two masonry walls on the former Midlands Railway viaduct has to do more than simply carry the 350t weight of the completed Waterpoint.

'At some point the new Thameslink tunnel will be bored directly below it - and we have to make sure there's no differential movement across the Waterpoint as a result, says Armitage.'

English Heritage comments: The moving of listed buildings is not generally endorsed by English Heritage as it dislocates the building from its important historic context.

In the case of the waterpoint it was seen, exceptionally, as a practical solution that would ensure the survival of a building that had been earmarked for demolition by the CTRL Act. The proximity of the new site to the building's original location, and the benefits that could be derived from an imaginative re-use of the structure in conjunction with the canal basin, were important factors in the project. The separation of the building into three parts, rather than brick-by-brick was also important. An early assessment showed that the strength of the original mortar would lead to the relatively soft bricks being damaged during dismantling, with a loss of the original high quality of detail that is such a clear reminder of the building's affinity with St Pancras station. A measure of the success of the project must surely be that the building looks perfectly at home on its new site, and will be more accessible to the public than it ever was in its original location.

Tank tactics

Designed by the office of St Pancras station architect Sir George Gilbert Scott, the three storey Grade II listed waterpoint includes similar ornate, finely detailed brick and stone features.

Its function, along with six long demolished siblings, was to feed the remorseless thirst of 19th and early 20th century steam locomotives from the 63,000 litre capacity water tank on its top floor.

This tank is made up of cast iron panels bolted together, with the joints caulked by 'rust joint cement', otherwise known as 'iron cement', a witch's brew of iron filings, sal ammoniac (ammonium chloride) and flowers of sulphur (a finely grained pure form of sulphur distilled from the mineral brimstone). Once mixed, the iron rapidly corrodes, the corrosion products expand, and the joint is sealed.

Sixteen internal wrought iron ties brace the tank panels against water pressure, eight cast iron beams support the weight and transfer loads into the pressed red stock brick walls. A lime/cement mortar was used, with very fine joints, and overall levels of workmanship was equal to the best Victorian standards.

Beneath the waterpoint lay part of the St Pancras Cellars, a series of brick arches which carried the adjacent rail tracks into St Pancras station. A brick parapet to the wall which forms the eastern end of the Cellars acted as the elevation of the first storey of the waterpoint.

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