Development of a high clay content earth plaster

Earth, as a building material, offers many advantages: on an ecological point of view, it is a natural, abundant, recyclable material with low energy used for production and transportation. Moreover, earth is known to be a natural humidity regulator and to improve comfort inside buildings, making it a good choice for indoor plastering. The clayey phase gives the global cohesion of the material by acting as a binder for the sand grain skeleton. The finest grain soil fraction is responsible for the dry strength, the water vapour permeability and the sorption capacity of earthen plasters. However, clay also induces the drying shrinkage of the mortar leading to the cracking of the plaster. The objective of this work is to improve the moisture buffer capacity of earthen plaster by increasing its clay content without jeopardizing the general behaviour of plasters. Based on consistency, shrinkage and shear tests, the characteristics of mortars in fresh and hardened states were evaluated. The hygric regulator potential of earthen materials were measured through the Moisture Buffer Value (MBV) test. As expected, results have shown that, to maintain a standard level of consistency, an increase in the clay content leads to a greater amount of mixing water. Moreover, to enhance the MBV, the highest possible earth content must be used. Addition of organic admixtures can be considered to improve the high-clay content plaster behaviour without jeopardizing the aesthetic and mechanical aspects of plaster.