Masons and conservators across the UK and beyond are rediscovering traditional mortars through research, use and experience. They are moving away from the default specification of Natural Hydraulic Limes for conservation works and are determined to practice like-for-like repair.
Conservation industry professionals including masons, conservators, architects, surveyors and engineers, assembled in York in June for the BLF three-day Symposium on Traditional Mortars held at St Anthony’s Hall, York and York Minster Stoneyard. A total of 165 delegates attended to present and discuss shifting perceptions and research regarding traditional mortars and their use.
Speakers presented recent experience using traditional mortars for the repair and conservation of historic fabric, sharing their insights and knowledge in theory and in practice. This included detailed presentations giving examples of hot mixed lime and earth-lime mortars in use by craftspeople around the UK and in Canada, as well as in Spain.
Day one focused on earth and earth-lime mortars about which there is growing interest. Fernando Vegas and Camilla Mileto gave a glorious overview of traditional mortars and building materials in the Iberian Peninsula. Ben Gourley presented on the use of earth-lime mortars in Western Canada and the context of their use by European settlers.
Alex Gibbons, a SPAB scholar working in the Solway Firth area on mud buildings, and William Skinner from Cliveden Conservation detailed the successful use of earth- and earth-lime mortars, surprising everyone with the simplicity of such success. Stafford Holmes made the importance of such endeavour clear in his discussion of flood and earthquake resistant earth-lime structures in Pakistan and Nepal.
Roger Curtis of Historic Environment Scotland also spoke about earth and clay mortars in Scotland giving insight into a current project to preserve the small fortified buildings, which were built using clay mortars, on each side of the Scottish Borders.
Other speakers included Becky Little, mudmason, and Tom Morton, architect, who talked about earth building past and present and Alison Henry of Historic England gave guidance and research about earth and earth-lime mortars.
Day two focused on the use of lime in hot-mixed mortars with presentations from around the British Isles and from Norway. David Wiggins, an engineer working for Curtins in Cumbria, explained the importance of free-lime in the delivery of effective porosity and capillarity within a mortar to achieve its effective functional performance in drying a building.
Bill Revie set out the material scientist’s perspective and offered information upon the identification of different binders – most of which were hot-mixed in the past. Eoin Madigan related his experience working with hot-mixed mortars in the west of Ireland and Phil Scorer, Vitruvius Conservation, detailed a large-scale project in the Cotswolds. Stone conservator Nick Durnan detailed his own very positive exploration of the potential of hot-mixed lime mortars, shelter-coats and limewashes.
Both Craig Frew and Roger Curtis discussed Scottish practice in an ever-wetter climate and Thom Kinghorn-Evans also offered insights into the use of hot-mixed air-lime mortars in wet environments such as West Wales.
Day three consisted of practical demonstrations at the Minster Stoneyard. Tours were given of the current works at the Minster which use traditional materials, including locally burned magnesium lime.
This BLF event was supported by Historic England and Historic Environment Scotland, with input from the University of York and York Minster.
Members of the Building Limes Forum form a community of lime enthusiasts and practitioners, most of whom are producers, suppliers, specifiers or users of lime.