Repair Mortars for Historic Masonry - State of the Art Report of RILEM Technical Committee TC 203-RHM

The authors of this report are the members of RILEM technical committee 203-RHM Repair Mortars for Historic Masonry which was created in September 2003 as a successor to RILEM technical committee 167-COM Characterisation of old mortars with respect to their repair. The aim of both committees was to develop methods and recommendations to improve the quality of restoration practices in the field of repair mortars for older (historic) masonry. An important reason for forming the committees was to give guidance on appropriate mortars and practices to avoid the many mistakes which had been occurring in practice in choosing repair mortars for existing masonry, thereby greatly increasing the risk of damage. Badly needed were recommendations based on the phenomena which play a role in regard to the compatibility of mortar and brick and aspects such as long-term quality and durability of masonry. The target group for this publication include architects, engineers, contractors and researchers. Committee 167-COM laid the foundation for the work by analyzing problems encountered in the field and describing test methods to determine relevant characteristics of historic mortars and substrates. In addition a general overview of the requirements playing a role with regard to repair was formulated. Committee 203-RHM focussed specifically on repair. The subject matter was formulated as follows: - Classification of types of historic masonry, types of repair problems and functional uses for repair mortars. - Development of technical performance requirements and design guidelines for compatible and durable repair mortars. - Only repair mortars with binders derived from limestone were considered. Examples of such binders are air lime, hydraulic lime and Portland cement. During discussions the committee soon arrived at the conclusion that the performance requirements for mortars may vary significantly as a function of the type of repair. Consequently, in this report the most important applications of repair mortars are treated in separate chapters: pointing, bedding, renders/plasters and flooring mortars. These chapters are preceded by a chapter on the role of mortar in historic masonry, a chapter addressing the decision process taking place between the analysis of the problem and the repair intervention, and a chapter on general performance requirements for mortars. The last chapter describes test methods for mortar which can be used for quality control and to assess performance requirements. During its existence from 2003 to 2010 the committee met twelve times. In addition it organised a workshop held in Delft, the Netherlands, in 2005 (see Rilem proceedings pro67). In 2010 summary papers of the committee’s work were presented during a workshop in Prague, organised in conjunction with the 2nd Historic Mortars Conference in Prague, Czech Republic (see Rilem proceedings pro78). The committee’s activities were carried out by an interdisciplinary group which included chemists, civil engineers, mineralogists, geologists, architects and building engineers. Unless otherwise noted, the photos were provided by the TC members and their organisations