Drying-Induced Cracking of Raw-Earth Plaster

The widespread adoption of raw earth materials in mainstream construction practices continues to encounter multiple challenges, where the main concerns with using earth plasters revolve around issues such as shrinkage, abrasion, and erosion (in the case of exterior application). This paper aims to provide a better understanding of the drying-induced cracking patterns of raw earth plaster. It first tackles plaster formulations with clay montmorillonite, with various sand and water proportions, where the latter is added until a consistent rheology is observed. The plaster workability is assessed by a rheological test to determine the yield stress. Then, we monitor the cracking behavior of samples under the form of a varying-thickness slab. From these experiments, we obtain conclusions regarding the impact of the thickness, substrate, and clay content on cracking patterns induced by drying. To understand these cracking patterns, an oedometer test is conducted to characterize the mechanical behavior of the materials. We also measure their air entry pressure and their drying shrinkage, as those properties play a significant role in the cracking phenomenon. This study will help to formulate a crack-free earth plaster containing swelling clays which are an abundant and affordable.