Mortars based on lime were once fundamental to most construction in the United Kingdom. Over the course of the twentieth-century these became eclipsed by cement mortars, with perceived superior properties. The demise of lime-based materials in building construction and repair was accompanied by a loss in understanding of their material properties, their fabrication and use. The deleterious effects of cement repairs in historic buildings and the benefits of lime were well acknowledged by the late twentieth century. However, the process of regeneration of largely defunct practice was fraught with limitations. By 1985 English Heritage instigated a proactive programme of field research at Hadrians Wall. This soon evolved into extensive laboratory investigations into the properties of mortars based on non-hydraulic, hydraulic lime and additives. This book will present the definitive account of the technical results of field and laboratory research, and the implications for best practice in the conservation and repair of historic buildings. It will be of interest to conservation architects and scientists, conservators and managers of the built environment.