Collyweston slate mine re-opens for Bodley’s repairs

Bodley’s roof is partially in disrepair. Photo: Claude N. Smith Ltd.
Bodley’s roof is partially in disrepair. Photo: Claude N. Smith Ltd.

As part of the College’s Strategic Infrastructure Programme, Bodley’s Court will be re-roofed in 2018 in order to replace the stone slating which has delaminated since being laid in 1893.

Bodley’s Court has housed hundreds of students, including Alan Turing, but is now in need of both external and internal renovation.

In order to preserve its listed building status, Historic England stipulates the importance of using slate ideally from the Collyweston mine to replace the roof, due to the local historical significance of the material, and replacing like for like.  This building has mostly Collyweston slate, as have many other buildings in Cambridge, perhaps the most iconic example being the Round Church on Bridge Street.  It is intended that the entire roof will be laid with the new stone, once extracted and split, in 2018.

The Collyweston mine, located in Northamptonshire, was re-opened with the support of King’s College and expressly for the Bodley’s roof slate extraction. The new seam holds approximately ten years supply, of which two years’ resource is needed for the project in its entirety. Extraction will commence in mid-January 2017, after which the stone blocks will be weather-proofed and split using an innovative ‘freeze-thaw’ method, which will emulate the natural annual lamination process of the seasons.  Thus a typical three year process can be reproduced in as many weeks, although the process in this case will be conducted at a more manageable and sympathetic pace.

The Clerk of Works, Shane Alexander, outlines the process:

“there is evidence that Collyweston stone (limestone) slate was used as far back as the Romans, slate is generally split into thicknesses by a skilled person using a hammer and chisel. Collyweston differs from this process by traditionally leaving the damp log (section of mined wet stone) on a bed of shale in the open air, to allow a natural splitting occurrence. This is achieved by allowing the log to freeze/thaw causing the layers (strata) to fracture, before using a cleaving hammer to pull the layers apart. Back in April 2014 Historic England recognised a shortage in supplying Collyweston slate for listed buildings, and tried to replicate the freeze method by placing the damp logs into a commercial freezer - the trials for this worked so well that several of the remaining mines have adopted this method, including Collyweston. We are also in discussion with the local conservation officer to install a secondary glazed unit for approval, keeping the appearance of the leaded windows from the outside the same (also due for refurbishment during the works), whilst improving the thermal loss.”

The Domus Bursar, Phil Isaac, oversees buildings management:

“this is one of approximately forty projects in the Buildings Portfolio of change, ranging from boiler replacement project to re-roofing Bodley’s, the Library, the Great Hall and then on to more ambitious projects such as new accommodation for Graduate students and an extremely exciting and ambitious project in the Chetwynd Courtyard.”

Look out for updates on the building’s programme in upcoming issues of King’s Parade. If you want to learn how you can support the buildings project at King’s, please get in touch with the Director of Development, Lorraine Headen (email to:lorraine.headen@kings.cam.ac.uk).

Read the history of Collyweston mining on the slater’s website: http://www.claudesmith.co.uk/

19 December 2016