Preventing water penetration in traditional masonry using injection mortar and micro-grouting conservation techniques

Abstract

Repointing is a universal repair technique applied to traditional masonry of historic buildings and, in particular, to ashlar masonry. Despite such long-established practices, on the British west coast at least, water penetration quite often recurs a few years after repointing has been carried out. These unfortunate statistics arise because repointing work, even when carried out well, is unable to fill open or deeply voided joints in ashlar masonry. New pointing is not always sufficient to restore the ability of a wall to shed water and prevent water ingress. At Burns Monument, Alloway, Ayrshire, longstanding water penetration caused the masonry to become saturated throughout and several repointing projects over previous decades had not stopped the ingress. Recent investigative surveys identified severe and persistent water penetration from deeply voided and open ashlar masonry joints. A comprehensive repair strategy was developed to robustly address these issues, which involved developing a new method of injecting hydraulic lime grout through its narrow mortar joints. This technique, known as micro-grouting, is able to reach and fully fill deeply voided ashlar joints in a way that has hitherto simply not been possible. During 2018–19 the monument was successfully micro-grouted and has begun to dry out. This paper aims to explain the issue of voiding in traditional solid wall masonry and the new conservation technique of micro-grouting and repointing by injection mortar by examining the case study of Burns Monument conservation project. Now developed, tested and successfully implemented, this new methodology can make an important contribution to improving the future conservation of other historic buildings across the UK and beyond, to restore the ability of many deeply voided masonry structures to shed water in a way that works with traditional lime mortar-based construction technology.