Learning from the Past: Rediscovering Traditional Medieval Wood Tar Adhesives for Sustainable Stone Conservation and Built Heritage

Abstract

This paper outlines a research project on the use of wood tar as adhesive for architectural stone repairs. Tar was identified as having been used in medieval repair techniques on Stavanger cathedral in Norway, as well as on several other medieval cathedrals in England and Germany. The hypothesis is that a complex adhesive mixture based on wood tar was manufactured and strategically employed by medieval artisans in northern Europe as stone repair material. Given that such repairs have withstood centuries of wear, there must have been extensive material knowledge and awareness of the complex requirements of structural adhesives. These historic tar repairs created the impetus for a research project, the aim of which is to rediscover the lost medieval art of traditional stone repair using wood tar adhesives, recreate the historic adhesive and repurpose it for modern conservation practice. By reintroducing traditional wood tar adhesives based on natural renewable source materials, we could potentially reduce dependence on synthetically manufactured adhesives. Thus, newly-discovered medieval techniques which have successfully lasted centuries will be drawn on to help solve the limited selection of suitable adhesives for stone conservation, contributing to future preservation of stone architecture and the built heritage environment.