Preliminary results for the use of micro-lime: clay soil grouts for plaster reattachment on earthen support

Abstract

A large part of China’s historic architecture is composed and built of earthen architectural components. The conservation of earthen architecture is therefore an important area in the conservation of China’s built heritage. Building surfaces often carry valuable information about its history and physical evidence on traditional materials and techniques. In-situ conservation of historic plaster is therefore seen as a crucial practice. This paper presents preliminary results of the ongoing research at the Architectural Conservation Laboratory at Tongji University on grout formulations for the conservation of plaster on earthen support. Traditional building materials, clay soil and lime, are used in this study, whose compatibility and long-term performance are known. It is also known that lime has, under certain conditions, a stabilizing effect on clayey soil. A common problem in the use of grouts containing clay is water brought into the structure with the liquid grout. The presence of water may weaken the historic clay plaster or dissolve and transport existing soluble salts. Micro-lime dispersed in propanol with a particle size range of 1-3 micrometer will therefore be utilized in the described tests. The advantages attributed to micro-lime include no limitations of penetration due to the particle size, and no mobilisation of soluble salts. Observations during the testing of grout formulations using micro-lime mixed with clay soil appear to show promising results in workability and performance; however, the grout performance is sensitive to climatic conditions. Tests will also be carried out to investigate if micro-lime particles penetrating into the historic earthen structure can enhance the stability of the historic structure and improve the adhesion between plaster, grout and substrate. The grouts have been tested in the laboratory, on mock-ups and on-site tests. Future testing will include the development of the grout performance over longer time periods and in varying on-site climatic conditions.