Can earthen plasters be effectively adhered to different substrates?

Earthen plasters have been widely used in historical buildings in northwest China, particularly in wall paintings. However, the properties of earthen plasters significantly deteriorate during long-term weathering. To investigate one of the key issues in plaster restoration, that is, whether the plaster can effectively adhere to different substrates, seven plaster compositions were prepared and applied to three types of substrates modeled after actual wall painting substrates. The radial shrinkage of different plasters during drying was measured, and the adhesion strength between the plasters and substrates was tested using a designed shear device after curing. The surface roughness of the different substrates was quantified using a three-dimensional scanner and correlated with shear strength. The adhesion properties were analyzed based on the microstructures of the different plasters. The results showed that the shrinkage of the plaster depended on its material composition and was almost independent of the type of substrate used. The addition of vegetal fibers to earthen plaster can effectively improve interfacial adhesion. The type and surface roughness of the substrate had a significant effect on the adhesion between the earthen plaster and substrate.