What three words? Quarry Mason Chapel

— 17 Aug 2023

Not a visit to North Dakota, but a continuing professional development (CPD) day for the Jonathan Rhind Architects team to learn about the challenges of the Killerton Chapel repair project and how the project team has overcome them alongside Killerton National Trust surveyors.

The day started with a trip to Exeter Volcanic Quarry near Copplestone where owner of the recently opened quarry, Andy Gray and geologist, Dr Kevin Page, spoke to the team about the unusual rock from which Killerton Chapel is built and which gives it its unique red and dark grey colour and weathering characteristics, also visible on Exeter’s Roman wall, parts of Exeter Cathedral and Crediton Church and other local historic buildings.   

A rock formation band exists roughly between Hatherleigh and Wellington where the tectonic plates between Britain and France collided, resulting in volcanic lava rising from 70-90km below the surface and depositing as lamphrophyric rock. In the words of Dr Page the rock from a volcanic vent (yes there were one upon a time volcanoes in Devon) is sadly not deep enough to produce diamonds, but does produce a very unique stone. Andy Gray also talked us through the trials and joy of reopening a disused and closed quarry and the process to follow to make this happen.

Lamprophyre - purple-grey in colour formed from lava flow, erupting onto Permian sedimentary 'red beds' of sandstones, siltstones and shales. The resulting volcanic stone is very unusual, and one of the main challenges for the project team had been sourcing a suitable replacement when most quarries were depleted or closed. We worked closely with the British Geological Survey (BGS) who after much searching elsewhere confirmed this stone was indeed a petrological match.

The group then moved on to see project stonemason stonemason Andy French’s workshop where Andy talked about the processing of the raw stone; how the stone is examined for cracks or deformities that would impact on the carving; and the assessment of the project templates to decide which would best fit each piece of stone. The stone is then carved ready to be installed on site. We also had some more in depth discussion of stone, the acidic or basic nature and how this can affect compatibility with other stones.

Following a local pub lunch next to the bubbling River Exe in Bickleigh, the team headed to the chapel to meet with Corbel Conservation carrying out the repairs and to discuss the challenges of replacing large pieces of carved ashlar; stone repair techniques and debate mortar matching to the original building mortar. Andy Coxall, Corbel’s mortar repair expert along with Project Architects Mark Raby and Simon Horler explained how the process of selecting the stone and mortar repairs was specified and arranged on site. James Wallace of the National Trust also helped the team understand the Trust’s key aims, the reasons for the project and the process his team undertook to set up the project.

To complete a very full programme we had a look at some of the stained glass repairs on the Chapel. Glass conservator and Director of Holy Well Glass Steve Clare talked about repairs to the intricate and iconic Rose Window which was recorded, removed, and repaired, before being refitted.

Due to the very complex form of the window there were some challenges in removing it. Holy Well therefore carried out subtle adaption to the lead cames, the framework supporting the glass, to allow future repair with less risk to damaging the precious glass.

Steve talked about glass painting techniques, their similarity to glazed ceramic and how this technology has adapted through the years. He explained cleaning and repair techniques and advised that conservators are brought in as a specialist early on in a project to be able to survey, advise, and provide costs and specifications. 

It is valuable for our team to regularly review ongoing projects on site and on the drawing board, to understand the different issues that might arise and how to solve them and to share ideas and solutions. A great day of CPD, with more to come.