Commenting on Collyweston stone slate

Catherine Bates and David Watt describe the results of some research.

Introduction
Collyweston stone slate is a traditional roof covering used in the East Midlands region of England. The material originates from the small village of Collyweston, located approximately four miles south-west of Stamford in the county of Lincolnshire, and was traditionally mined from a number of sites in or near the village.

Once brought to the surface, the Collyweston 'logs' were naturally frosted, split or 'clived' in regular thicknesses, dressed, and 'parted up' into individually-named sizes. The slates are traditionally hung on bat- tens using either oak pegs or small animal bones, and bedded on a lime- based mortar.

Changes in farming practice during the late 1950s and early 1960s gave rise to a growing number of redundant traditionally-slated farm buildings. As farm machinery increased in size, many of these buildings were demolished, providing a plentiful supply of suitable reclaimed material. The mining of new slates thus became uneconomical and most of the mines were forced to close.

This source of reclaimed Collyweston stone slates is now itself becoming exhausted and the use of cheaper substitutes (replica concrete or fibreglass slates) has become increasingly common. The Collyweston Stone Slaters' Trust (founded in 1974), English Heritage, local authorities and others are now investigating ways in which to support a revival in the supply and use of new stone slates.

A short-term research project was initiated at the suggestion of the Collyweston Stone Slaters' Trust to study the current state of funding for Collyweston stone slating and for the buildings that have Collyweston stone- slated roofs. The project also exam- ined the use of replica slates, the attitudes of local authorities towards existing and new Collyweston slated roofs, local policies relating to the use of these slates, and general knowledge concerning the industry. The project was undertaken by Catherine Bates, a Building Surveying student at De Montfort University, Leicester, with funding from the De- partment of Building Surveying and the Centre for Conservation Studies. Copies of Collyweston Stone Slates by Catherine Bates are available on payment of £2.50 (inclusive of postage and packing), payable to De Montfort University, from Dr David Watt, Centre for Conservation Studies, De Montfort University, 12 Castle View, Leicester, LEI 5WH.
Bad Practice: The slates on this rool in Fotheringhay, Northamptonshire have been 'stretched' to reduce the number required. The end lap on the slates had been reduced (notice how part of the originally protected slate is now showing) and the width of the side joints has been increased (these have been finished with mortar).
Good practice: Collyweston slates being relaid by David Ellis, Collyweston Stone Slater, af Ryhall, Lincolnshire, on a house in Cotterstock, Northamptonshire. the slates are 'parted up' according to size on the scaffolding ready lor use, and are being laid in traditional manner using small pieces of slate or 'shales' to improve resistance to rain penetration and ensure an even finish.

Sources of new, reclaimed and replica stone slates
Questioned about the availability and use of new, reclaimed and replica stone slates, the responses of a number of stone slaters and building contrac- tors were as follows:

  • most of the individuals stocked and fixed concrete replica stone slates and/ or reclaimed stone slates;
  • they obtained their stock of concrete replica slates from: main distributors such as Bradstone or Atlas Stone products;
  • they obtained their stock of reclaimed stone slates from:
    old farms or outbuildings that have    Context 58 June 1998
    been re-roofed with another form of covering
    the rear slopes of buildings
    previous jobs
    personal stocks
  • only two of the individuals contacted stock new Collyweston stone slates;
  • delamination occurs on new slates and once this has occurred the slates remain the same for years;
  • slates last longer in rural areas as there is less pollution than in the towns;
  • reclaimed Collyweston is not that much cheaper than new Collyweston stone slate;
  • not all the slaters have had proper formal training;
  • no one stocks glass fibre replica slates; and
  • slaters who had come across glass fibre replica slates replied that they were not very good. Due to the varying climatic conditions in this country, the glass fibre slates warp and twist unless they are fastened securely at all four corners. They also become very brittle in a short period of time.

Current cost of new, reclaimed and replica stone slates
At the time of undertaking this project (1997) the cost of supplying and fixing a basic roof with new Collyweston stone slates (inclusive of battens and underslating felt) was £1,200 + VAT per square (100 square feet), or £129 + VAT per square metre.

To supply and fix a basic roof with reclaimed Collyweston stone slates costs £960 + VAT per square, or £103 + VAT per square metre. In 1986 a comparable cost was recorded by the author (DW) as £400-£500 + VAT per square, or £43-54 + VAT per square metre.

To supply and fix a roof with concrete replica stone slate (Bradstone or Atlas Stone Products) will cost about £232 + VAT per square, or £25 + VAT per square metre.

Sources of new Collyweston stone slate
Only two slaters, David Ellis of Staniford and Claude Smith of Collyweston, supply new Collyweston stone slates.

David Ellis has been a Collyweston stone slater for 44 years and in 1961 set up his own business. Since then he has trained nine people in the selection of slate log, six of whom still work for him. In 1982 he discovered a large area of Collyweston log and successfully frosted and split a sample. He extracted 50 tons of log in 1985, and has since quarried and split 750 tons of new Collyweston log.

Claude Smith owns a mine at Collyweston and employs 10 slaters who are qualified in laying Collyweston stone slate roofs.

Information from local authorities
One of the aims of this project was to establish what local authorities with Collyweston stone slates in their regions knew about the slates, and how they protected stone-slated buildings.

Nine (out of 12) local authorities in the East Midlands region responded to a questionnaire, and provided the information shown in the table.

Conclusions
The conclusions drawn from this project were as follows:

  • Collyweston stone slates are widely used within the local area of production;
  • the majority of local authorities are aware of the existence of Collyweston slate-covered roofs, and most buildings are either listed or in conservation areas;
  • despite the planning controls that should apply to Collyweston roofed buildings, several examples have been found of buildings in conservation areas that have been re-roofed with other roofing materials that do not attempt to match the true Collyweston stone slate;
  • specific funding for repairs to Collyweston slate roofs using new Collyweston slate is not widely available;
  • from limited discussions with owners of buildings with Collyweston slate roofs, it is believed that this is a cherished form of roofing and individuals make efforts to maintain the roof in a good visual state of repair;
  • some owners have used replica materials such as concrete and fibreglass. It is felt that the concrete replica slates are better in appearance and durability;
  • buildings that have been constructed in and around the Stamford area in the recent past have had to use a roofing material that blends in with Collyweston slates. In most cases concrete replicas have been used, which, although strikingly coloured when new, weather over a short period of time to a more natural tone; and;
  • some builders who have laid concrete replica slates have not made an effort to lay the slates to diminishing courses, but others are more realistic and even reproduce laced valleys.
Catherine Bates is a final-year student on the BSc(Hons) Building Surveying course at De Montfort University, Leicester, Dr David Watt is Senior Research Fellow within the Department of Building Surveying at De Montfort University, Leicester.

Context 58 June 1998