St Ninian’s church is a category B listed mid Victorian gothic stone church on the south side of Glasgow. The church experienced structural disturbance during a period of extensive ground piling works on an adjacent site, when the west gable of the church and it’s fine stained glass window comprising 5 lancet lights and a rose at the head suffered severe sudden trauma. A condition survey carried out before the adjacent building works began had recorded the stained glass had no defects, and stonework was fragile from years of periodical weather erosion, but intact. Over a few of weeks, cracks appeared in tracery joints and mullion bases with cills splitting, cracks to wall plastered, cracks to a door stone arch and the stained glass pulled apart on the line of leading from the top to the bottom of the window, through the rose and second lancet.
A scaffold was erected internally and digital monitoring of the cracks with telltales took place over a nine month period until construction groundworks on the adjacent site were complete and it was apparent no further significant movement occurred after the initial event. A detailed inspection of the cracks and damage identified the need for a combination of repairs, and the architect and structural engineer scheduled a specification of conservation and restoration to the stonework and glass. The two damaged windows were removed for repair of the leading in the stained glass conservators' workshop and samples of stone, mortar and plaster were analysed by the Scottish Lime Centre and British Geological Society to determine the best matching specification for repair and replacement.
The stained glass is of exceptional quality from the late Victorian workshop of Heaton Butler and Bayne. Repairs to the glass required re-leading the damaged joint strips but it was found that these were limited within the window to the weak areas affected by rain penetration and only very few sections of glass had been damaged and required matching replacement. New copper ties to cams were also provided.
The removal of the glass from the stone mullions had not been easy as the sacrificial margin leadwork was narrow and had been re-pointed into the stonework with a cement rich mortar during some repairs in the past. The window removal caused damage to the interior face of the stone mullions and repairs were going to have to include repairs to the full height. To save losing the mullions which were substantially sound, Lithomex built up lime mortar repairs were carried out by the mason in selected colours to match the adjacent stone.
The approach to repairing the stonework and tracery was based on minimising further disturbance to the structure of the tall arched windows which had now stabilised, but a little out of alignment from the original construction. In several places weak faces had sheared off and some joints had opened up with old mortar falling out. Three methods were used to make good open joint and cracks: stainless steel dowels to tie wide voids, resin injection to narrow ones and lime mortar fill and repointing to all open damaged joints. Most of the curved insets of the foliated rose window were so friable that they sheared when the stained glass was removed, and partial indents were required.
Two mullions were cracked right through close to the cill and partial indents were needed. These were carried out with extreme care to avoid any further movement and involved two scaffolds, inside and out, tied through the window openings and the cut mullions being carried on support steels while the inner and outer damaged sections were cut away one after the other and quickly replaced with pre-cut stone indent sections. The result was successful with no further damage.
Cracked plaster and it’s lath was cut away to expose the stonework of the wall, where only minor cracking was found, requiring repointing. The analysis of the original lime plaster, confirmed a specification to match, including bovine hair for binding the lime plaster mix.
For health and safety of the masons working on the repairs, a considerable amount of pigeon mess had to be very gently washed and scraped away externally from the damaged stonework before repairs could begin, and discrete stainless steel pin strips have now been fixed to ledges to deter birds from roosting.