20 Apr Holborn Bars
Holborn Bars is a Grade II* listed building in the borough of Camden on the boundary of the City of London. Construction started in 1878 under architect Alfred Waterhouse and was then modified thereafter in phases by his son Paul Waterhouse, being finally completed in 1932. Waterhouse was perhaps most well-known for his design of The Natural History Museum (built 1865), and although on a smaller scale, the Victorian architecture of Holborn Bars is equally representative of the Gothic Revivalist style. It is constructed from red brick and Terracotta and includes the typical decorative patterns, finials and lancet windows associated with the period.
It is currently occupied by De Vere Venues and houses the London office of English Heritage.
The name Terracotta came from the Latin for ‘baked earth’. It has been used as a building material for centuries but gained widescale popularity in England toward the latter half of the 19th Century. Its popularity was in part due to the fact that it could be mass-produced, was lightweight and mouldable and was also both fire and pollution resistant. Terracotta can be produced in both glazed and unglazed forms, although glazed units are normally referred to as Faience. The period between the 19th-20th Centuries was an exciting time in construction, with many new materials and techniques being developed which enabled wider spans and faster construction times. With this obviously comes the economies of cost from fewer materials and in turn a reduction in labour.
It was last restored in 1993, with much of the façade being extensively cleaned. Prior to this however, we understand anecdotally, it was cleaned with a strong acid in the 1970’s. The effect of this has been to damage the fireskin of the units, which has then exposed the porous body of the clay beneath and makes the terracotta more susceptible to soiling and breakdown. Acids have been used for cleaning to good effect in the past, but the key, is in using the correct contractor who understands both processes and limitations of the materials. In the right hands, soiling can be removed without any damage to the units, conversely, in the wrong hands irreparable damage can be caused.
The overall impact of this previous cleaning has been to expose the more porous centre of the terracotta which now absorbs airborne particulate at a much faster rate. Ironically, this inappropriate cleaning has now exacerbated the rate of decay and forced a more regular maintenance regime. Temptation from client side, may be to conduct a more aggressive approach to counteract this. PAYE’s recent survey and report, however, helps the design team establish an approach to conserving and restoring the façade whilst managing expectation of what can be achieved.
Cleaning with the Doff
As such, we have only recommended that the building is cleaned with the Doff. As has been explained in previous issues, The Doff is a building conservation specific superheated pressure washer which allows good control over both pressure and temperature – allowing the use of cold water at minimal pressure, all the way up to a constant steam temperature of 150 degrees at pressures of up to 90 bar. This will flexibility in the approach to cleaning whilst ensuring no further damage is caused.