Clerestory Works – Next Phase

As the next stage of the repair work to the Cathedral clerestory begins, the Cathedral Organ will be covered internally with plastic sheeting to protect it from dust and dirt. The organ console, from where the instrument is played, will also be boxed in. We will be without the organ for the duration of the work, and so will be bringing our wonderful Steinway piano into its own to accompany our worship. Choral services will continue as usual during this period, with the Cathedral choir returning to their duties from Thursday 11 January onwards. We look forward to having the organ back during the latter part of Lent.

The cathedral roofless during the war
The cathedral roofless during the war

Background to the Project

The Bathstone ‘detached’ shafts at clerestory level are splitting due to internal corrosion of iron cramps used in the re-construction of 1859 to tie the shafts to the surrounding stonework.

When iron corrodes it expands considerably, with enough force to split stone. It is likely that moisture got into the stone following the bomb damage in 1941 (when the clerestory was left exposed to the elements until the current roof was installed in 1953), and this moisture has accelerated corrosion of the iron.

Each of the 84 Nave and 12 West Front internal detached shafts will be carefully dismantled to remove the embedded ironwork and repair the stonework. New stainless steel cramps and dowels will be inserted, and the shaft stones will be repaired and reinstated in their original positions. The surrounding stonework will have a light clean to remove the worst excesses of carbon encrustation.

Repair methodology
Repair methodology
The effect of corroding iron cramps on the stonework
The effect of corroding iron cramps on the stonework

The dowel hole and cramp inside a shaft
The dowel hole and cramp inside a shaft
Ancillary Work

The cost of scaffolding the entire Nave and Choir is considerable, and it will make sense to do as much work as possible while the scaffold is in place.

The clerestory windows will be repaired and cleaned as part of the project. The leaded windows are secured to horizontal iron tie bars. During the 1950s restoration the tie bars were attached to brass spigots which were embedded into notches in the reveals of the windows with hard mortar. Most of these fixing spigots are now loose. This causes the windows to rattle with wind pressure and even when the organ is played, which in turn leads to cracking of the glass.

Stainless steel angle sections will be installed to hold the existing brass spigots against the stone reveals, to avoid dismantling the windows (a very expensive process). The brackets will be toned-down to make them less noticeable – the recipe involves a mixture of gold size, pure turpentine and burnt umber pigment. The plain glazing also needs a thorough clean inside and out, and this will be done carefully with cotton swabs.

Spalling window stonework around glazing tie bars
Spalling window stonework around glazing tie bars
A prototype of the glazing bracket
A prototype of the glazing bracket

 

 

 

 

 

 

 

The 1953 hardwood ceiling is stained in places from past roof leaks, and these stains will be also removed in areas that can be accessed. Render will also be repaired and re-decorated.

Training Initiative

The project includes a training programme of five three-week training blocks for trainees who are considering a career in building conservation.

The Programme

Scaffolds will be erected in phases between June and November 2017 and from January to April 2018, with breaks for key events and festivals in the cathedral. The work will mean some disruption to visitor access and services at times, and this will be communicated to visitors and the local community throughout the project.