Characterization of earthen plasters – Influence of formulation and experimental methods

All over the world there is a vast heritage of earth construction where earth plasters were applied. Nowadays, due to environmental but also technical reasons, new earth plasters are also applied on common new masonries. That is why its characterization, in the laboratory but also in situ, is very important. In the present study, a pre-mixed earth plastering mortar (as control) and nine earth-based plastering mortars formulated in laboratory with different compositions were characterized. These mortars were formulated with 1:3 (illitic clayish earth:aggregate) volumetric ratio. The aggregate comprises a variation of fine and coarse sand and the partial replacement of the fine sand by a phase change material (PCM). The influence of the addition of a low amount of oat fibers is also evaluated. The mortars were characterized by different methods in laboratory and on an experimental wall exposed outdoors by destructive and nondestructive methods: dry bulk density, ultrasonic pulse velocity, dynamic modulus of elasticity, flexural and compressive strengths, adhesive and shear strengths, dry abrasion resistance, surface cohesion and hardness. Results were discussed and some were correlated. Most mortars present good mechanical strengths. However, the addition of PCM significantly decrease the mechanical strength of mortars. In terms of mechanical properties, the addition of oat fibers only promotes an improvement on adhesive strength. The simple surface hardness by durometer present laboratory and in situ results well correlated for earth mortars without PCM.