A building stone and slate survey of the Callander Conservation Area : recording, matching and sourcing for the built heritage

The town of Callander is the eastern gateway to Loch Lomond & The Trossachs National Park. This report describes the background to, and outcomes of, a survey of buildings and other structures comprised of natural stone and slate in the Callander Conservation Area (CCA). The survey was conducted by the Building Stones Team of the British Geological Survey (BGS), for the Scottish Stone Liaison Group. The survey data and other project outcomes will be used by Loch Lomond & The Trossachs National Park Authority to inform planning decisions, with a view to safeguarding the built heritage of the CCA. A total of 382 structures were surveyed between February and May 2010. With the exception of one bridge and two monuments, the surveyed structures consisted of residential, commercial, ecclesiastical and civic buildings. Survey data were recorded on hand-held PC tablets running the BGS ‗SIGMA‘ system for digital field data capture. A 'Building Stone Data Capture' module was designed specifically for the project. Data describing the character and condition of stone and slate were gathered for separate architectural elements (walling, dressings, and roofing) in each surveyed structure. A set of predetermined data fields guided and restricted the range of properties that could be recorded, and a set of supporting dictionaries (with definitions, where appropriate) restricted the range of terms that could be used to describe each property. The recorded data have been transferred to a set of data files that can be interrogated independently or used within a GIS application. The survey methodology is described, and details of the database hierarchy and supporting dictionaries are presented. The main outcomes of the survey, in terms of the range of stone and slate types used in surveyed structures, their distribution in the CCA and current condition, are described. Four masonry styles (i.e. particular combinations of stone type, block size/shape/tooling and coursing used in the main architectural elements of a building) are recognised in the CCA, each reflecting the available building materials, architectural tastes and masonry skills of the time. The main changes in masonry style can be linked to events affecting the availability of materials, in particular the opening of quarries in the local area (providing a reliable but restricted source of local building stone), the arrival of the railway (bringing a variety of stone and slate types from other parts of the UK), and the impact of the First World War (associated with a rapid decline in the number of operational building stone quarries in the UK, and a shift to ‗modern‘, manmade building materials). Three of the most important stone types used in Callander buildings - conglomerate (Callander puddingstone), and two types of flagstone - were sourced locally, from three long-disused quarries in wooded slopes north of the town centre. These quarries are overgrown and neglected, but they are not filled or flooded. They represent the most obvious sources of matching stone for these stone types, to be used in future repairs to existing buildings and new-build constructions. If re-opening these quarries proves impractical, sites for potential new quarries could be identified by examining ground along strike of the bedrock strata exploited by the original quarries. Three types of blonde to buff sandstone and four types of red sandstone are also recognised in Callander buildings. One of the red sandstone variants was probably sourced from one of the three local building stone quarries, but the other types of sandstone were imported from quarries in the Central Belt of Scotland, Dumfries & Galloway, and Northumberland. Potential matching stones are listed for each stone type, but this information is intended only to be a general guide; a formal stone matching exercise should be carried out whenever replacement stone is required. Scottish Highland Border slate and Welsh purple slate are by far the most commonly used roofing materials in the CCA, and have been used on approximately equal numbers of buildings. English (Cumbrian) slate and Spanish slate have been used on approximately equal numbers of buildings, but are much less common than Scottish and Welsh slate. The most serious causes of stone decay in the CCA are cement pointing and patchwork, face bedding, and failing rainwater goods. These are described, and best practice guidance for conservation and repair of affected buildings is provided. Slates that have moved out of correct position constitute the most important roofing condition issue in the CCA. A survey of stone condition in the 'Desirables' building, at 1-3 Main Street, is presented as a short, stand-alone report (in Appendix 3). The report is intended to be a template for future surveys of stone condition and maintenance issues in individual buildings.