“Plastic” repair of natural stone in Scotland: perceptions and practice

Purpose – The purpose of this paper is to address the issue of perceptions of suitability of different materials for a repair. The use of highly cementitious materials in the repair of historic masonry is causing great concern due to their incompatibility with adjacent stone and the associated accelerated deterioration which results from their use. The relatively recent development of so-called “restoration mortars” based on a “mix and go” application, combined with the enhanced weathering of stone in a changing climate, may be contributing to the use of “plastic” repair materials on stone across Scotland.

Design/methodology/approach – Following a literature review, case studies of repairs are presented to highlight the advantages and disadvantages of using such materials, and comparisons are made with the alternative options.

Findings – The case studies presented highlight the use of a number of different stone repair materials, sometimes in combination with stone replacement, representing functional and philosophical approaches to masonry repair. However, the research has also highlighted the increasing use of plastic repairs for large-scale repair including façade rendering, which fail to incorporate these systematic and informed approaches, and can ultimately lead to failure of repairs.

Originality/value – An evaluation of the current standing of the materials, methods and the extent of this type of repair, is vital for the substantiation of further research, and to enhance the empirical knowledge of in-use performance, longevity and failure. The increasing emergence of restoration mortars, and their manufacture and supply on an international scale, highlights the global impact and relevance of this research.