Lime mortar technology was introduced to Ireland during the early medieval period (AD 500-1000), and was used for a wide variety of purposes in the medieval and post-medieval periods, including general building, internal plastering and external rendering, and for special purposes such as chimney flues and wicker-centred vaulting. A wide range of mortars are found in Irish medieval and post-medieval buildings, ranging from lime mortars used in tenth century churches and round towers to Roman cements and the often highly complex materials found in more recent times. These mortars were used for bedding and pointing masonry, for rendering external walls, and plastering the interior of these buildings, as well as more specialised applications. Decorative plasterwork also survives in a range of forms, ranging from the imitation of ashlar work on building exteriors, to the ornate freehand modelling, cast and moulded work of Irish stucco. Analysis of historic mortars is carried out from three distinct, though interlinked, perspectives:
- Conservation: focusing on understanding the characteristics of a mortar, its degradation and interaction with the rest of the building fabric, and most often to obtain specific information to formulate a compatible repair mortar.
- Archaeology: focusing on introduction and development of historic building practices, determining the provenance of raw materials, on production processes (lime burning, mortar mixes, use of additives etc.), and also to provide absolute and/or relative dating evidence for a particular site or structure.
- Historic Materials Research: analyses which aim to increase knowledge and understanding of burning, mixing, hydration and carbonation processes, and identifying the different minerals formed.
The purpose of this project was to summarise, compare and contrast the analytical results of the petrography and microstructure of medieval and post-medieval mortars in Ireland accumulated through research and consultancy work over a 13 year period. These mortars included a wide range of historic lime mortars from archaeological sites such as round towers, Anglo-Norman castles and other medieval fortifications through to Georgian and Victorian decorative plasterwork, and also natural cement or ‘Roman’ mortars, early Portland cement mortars and hybrid mixes. The project was intended to provide an increase in knowledge of historic lime mortars and construction practice, and improve the specification of repair, replica and replacement mortars used for the conservation and repair of Ireland’s historic buildings and monuments.
The project was funded by The Heritage Council under the 2010 Heritage Grant Scheme. Part of the research was published as:
Bolton, J. (2010) “Irish Medieval Mortars: Implications for the formulation of new replacement mortars” as part of the 2nd Historic Mortars Conference & RILEM TC 203-RHM Repair Mortars for Historic Buildings Prague, 22-24 September 2010 and published by the Institute of Theoretical and Applied Mechanics of the Czech Republic & RILEM.
A further research paper was published on a specialist case study: Bolton, J. (2010) “Conserving historic buildings: the problem of ‘black lime’ mortars” Journal of the Building Limes Forum, Volume 17, Pp. 28-31