Case study: Temple Bar
Temple Bar was once the portal on the Strand marking the boundary between the City of London and Westminster, and is the last surviving of London's eight perimeter gates. Moreover, it is one of the capital's great Baroque monuments. The two-storey structure was built during 1670-72 in Portland stone and, although in the style of Christopher Wren, it is not thought to be his design. It features two slim pedestrian arches flanking a flat road arch that supports a pedimented first-floor room decorated with niches that once held busts of monarchs and which is braced by fluent consoles.
Just over a century ago it was removed but this November will return home (just) as the gateway into William Whitford's Paternoster Square scheme.
In 1878, as an obstacle to stagecoaches entering Fleet Street, and deemed incongruous with G E Street's new Law Courts, it was dismantled and sat in pieces in a builder's yard for a decade. A former London barmaid, Valerie Meux, discovered it and perusaded her husband, Henry Meux, to re-erect it with a new gatekeeper's lodge attached at Theobalds, their Hertfordshire estate. In the mid-20th century it became roofless and derelict. In the 1960s, William Holford intended to re-erect it as part of his Paternoster Square scheme, but the proposed site was deemed too close to St Paul's. Vandals took their toll before it was bundled into storage.
In 1976, the Temple Bar Trust was set up to campaign for its reinstatement in London. Work began in earnest in 1982 when the late David Roberts subcontracted Henry Freeland as conservation architect, who set to work on measured drawings. The first task was to put a temporary roof over the building, as if a blanket over a patient, and to clean off the worst grime. For this, Freeland chose the Hodge Clemco system (a low-pressure dry calcite abrasive), followed by a biocide treatent of Panacide M. Temple Bar needed two things: an appropriate site and serious funds.
By the mid-1990s, the obvious location was the by now royally maligned Paternoster Square, the most significant new development scheme near Temple Bar's original site. The costs were set at about £3.5 millon and funding was secured from the Corporation of London.
Portland stone is excellent for the city atmosphere as it is far less prone to spalling by encrusted sulphur dioxide than, say, Oxfordshire limestones.
Freeland looked closer at the building, and found that much of the damage was due to impact rather than erosion. Some of the capitals had been damaged while others, apparently in good condition, were Victorian replacements with inferior carving. Soon it was obvious that Temple Bar was lucky to have capitals at all, for all the pilaster bases were missing, apparently engulfed by London's rising street level over the course of two centuries.
Inspection of engravings showed that the gate also once bore sculpted heraldic arms: for the sake of a complete job, they also had to be replaced.
Three sculptors competed for the job, and Tim Crawley won.
The main tender was awarded to Chichester's Cathedral Works. Its experience of the dentistry techniques required for unpicking historic masonry met a challenge when it became clear that Meux's reconstruction of Temple Bar had set the lower half in something akin to concrete, while the upper storey's blocks were bedded in a sandy paste. This is just one example of why it is wise to build in a contingency of at least 15 per cent for this kind of project. The reconstruction is going ahead with a mix of one part hydraulic lime, two crushed Portland stone, with St Astier limestone - mixed as NHL (natural hydraulic lime) 2 specification; NHL 3.5 for the heavier loads in voussoirs, stone ribs and arches. The pointing specification is two parts graded Portland stonedust, one part slaked lime putty.
Building conservator St Blaise produced a report on trial cleaning and coating. A general shelter coat was suggested to complete the rebuilding, as traces of whitewash were found on the monument surface, but tests of 1:1:1 Portland stonedust, Bath stonedust and slaked lime putty soon blistered, whereupon a stronger version was chosen for only small local repairs and protection. In assessing the repairs, St Blaise worked with consultant conservator Deborah Carthy, who highlighted Portland's potential to brown from some poultice treatments, and formulated a mix of 10 per cent ammonium hydrogen carbonate in sepiolite clay with water. For plastic repairs, a Belgian stonedust-based product called Lithos Art was selected, to be augmented with armatures and tinted to match the Portland. Shelter coats will not be applied to these repairs as they can cause the surface to darken. Work continues apace on Temple Bar and, in just a couple of months, one of London's finest pieces of stonework will once again grace the city, which more than compensates for the loss of a folly at Theobalds.
Further reading The late Alec Clifton-Taylor and Anthony Ireson (a Northamptonshire mason) together wrote English Stone Building (1983), and Clifton-Taylor's The Pattern of English Building remains a highly readable introduction. Still the best book relating geology to quarrying and building is the scarce Oxford Stone by W J Arkell (1947). The major contemporary scholars of archaeological stonework include David Parsons, Richard Morris, Tim Tatton-Brown, Jennifer Alexander and David Stocker, who continually revise the evolution of many of our famous buildings in the volumes of the British Archaeological Association, among others. Tim Eaton's PhD thesis on the reuse of Roman stonework in the Middle Ages is published by Tempus as Plundering the Past (2000). A raft of excellent local books includes The Building Stones of Shropshire by M Ann Scard (1990).