RETENTION OF HISTORIC FABRIC, REPAIR AND SYMPATHETIC RESTORATION
CILL REPLACEMENT – ELEVATION I
The replacement of the cill detail to 2 no. windows identified on Elevation I with geologically matching limestone (Tadcaster) consisting of three main elements including cill, rusticated panel below and plinth course at low level.
The existing jamb and bearing elements remained in position and this helped with temporary support by their very function.
A sequence of work was chosen to ensure a systematic process and a practical solution utilising mechanical aid for the larger sections and manual handling only of the smaller sections that could be installed at the end within the pockets formed.
A tiger 1000kg mobile lift table was used for the vertical and horizontal transfer of the cill(s) and rusticated panels. The lifting table has a manual hydraulic operation and is lifted by a foot operated pump unit infinitely controlled dead man release trigger.
The cill was carefully transferred to the work area using the table lift. Due to the position of the scaffold, the cill was lowered on to timber rollers at ground level and simply orientated to the correct position between the face of the building and the internal standards of the scaffold. Once the cill was aligned centrally with the window, the table lift was used again to raise the cill to its installation height.
The cill was carefully lowered on to a prepared bed of hydraulic lime mortar at either bearing end. Once in place and fully weighted, the table lift was lowered and removed.
All mortar that squeezed out of the bed was removed and joints finished accordingly as per the agreed specification.
The rusticated panel below the cill course, was then transferred and positioned using the same protocol and techniques.
The smaller, lighter and manageable moulded limestone plinth stone will be installed by hand by a team of masons together the lower sandstone blocking plinth stone.
Lead Capping Detail
The Introduction of a code 5 lead flashing to the mid level cornice with welded joints, drip detail and flashing arrangement to the abutment with the main building provides protection to the cornice and historic stonework below. The drip detail will aid water circuitry and will allow rainwater to be discharged away from the building line therefore helping to extend the lifespan of the building.
This subtle intervention has minimal visual impact from the ground however excellent functional value and should be promoted from a conservation perspective.
REMOVAL OF OFFENDING FIXINGS AND REINSTATEMENT OF STRUCTURAL INTEGRITY
Ferrous metal cramps and fixings were extensively used during the construction of this significant Listed Building. Although the original intention of these fixings was to bond and connect adjoining pieces of stone together, they often forced them apart.
To explain, general weathering and water penetration attacks the fixings, causing corrosion to occur and in turn expansion. As a consequence, rust jacking and delamination of the stone fabric takes place, setting up a cycle of progressive deterioration and often structural displacement.
The effects of this were clearly visible on site at the base the pilasters where very substantial twice turned cramps were utilised at the connection point. Physical damage was evident with some signs of movement apparent.
The scheme of repair involved the removal of the offending articles, ensuring maximum retention of historic fabric and minimal intervention. Temporary support was provided to the bearing sections of the pilaster before replacement bases, masoned to the original profile using geologically matching limestone sections were installed.
REPLICATION OF MISSING TERRACOTTA BALUSTERS AND SYSTEMATIC DISMANTLEMENT & REBUILD OF PORTICO PARAPET
Following the careful removal of handrails, individual balusters and die blocks from the portico parapet including certain base blocks which exhibited signs of rust jacking, the base was prepared with a bed of lime mortar.
The base blocks were then re-fixed with new stainless steel cramps as required ensuring a level base was created throughout ready for the actual balustrade parapet to be assembled.
The corner die blocks were then fixed in position using running lines to ensure verticality and alignment was maintained.
The balusters were then connected to the base using stainless steel dowels set in a thixotropic resin and the existing and new handrails carefully transferred and placed on top. Again stainless steel dowels ensured firm connection.
Once the handrail was in place to the full length, stainless steel cramps were installed between each handrail joint as an additional precautionary measure. All remaining joints were pointed with lime mortar (NHL 5.0).