Three phases of conservation work at Balliol College, Oxford was amply recognised at the Oxford Preservation Trust Awards in November. The elevations on Magdalen Magdalene Street East elevation of Balliol after conservationStreet were initially cleaned using the Thermatech steam cleaning system: an efficient way of removing organic grime. Any sulphation was then removed using the Vortech system. The stonework was surveyed and the condition of each stone was individually assessed, with conservation, not restoration being the guiding principle.
Any remedial treatment was then assigned: consolidation, repair with lime, repair with stone, replace completely in stone. Any mortar repairs were undertaken using a combination of putty or hydraulic lime, gauged with washed sands and dusts to give a suitable colour and texture. The elevations to Bristol, Basevi and Henry Keane are constructed from fine-grained Bath stone, Salvin from Box Ground, 1912 Warren from Clipsham and 1906 Warren Building from Guiting. Much of the Bath stone is held to a brick core with iron cramps, many of which had rusted and spalled the stone. Replacement stone used was Hartham Park Bath stone from the mine at Corsham, except for Clipsham for the plinth to Henry Keane Building and Box Ground for Salvin.
Much of the damage to the window surrounds and the string courses to Bristol and Basevi had been previously repaired in a white cementitious mortar. Some of this stone had continued to decay and the stone was replaced. However some of the repairs were still sound with good detail, but however unsightly: it was decided to treat these using an Earthborn silica paint (seen as a more robust solution to a traditional shelter coat), blending in the repairs and consolidating vulnerable areas between the cement mortar and stone.
Other repairs included replacing/renovating existing leadwork, minor roof repairs, joinery and rainwater goods redecoration.