Assessing the Use of an Earthen Mortar Coating as a Fire Protection for Bio-Based Earth Masonry

Bio-based materials, valued for their low environmental impact, sometimes exhibit a vulnerability to fire, which limits their use in construction. This study investigates the use of earth mortars to improve the fire resistance of bio-based earthen blocks masonry. The blocks were manufactured by extrusion earth using earth combined with sawdust. The earth mortars were formulated using an optimized mixture of silty-clay earth combined with silica-calcareous sand or fired brick waste. These were applied either as 10 mm thick bedding mortars on small wall samples composed of three blocks, or as 20 mm thick coatings on these wall samples. Three groups of wall samples were tested: uncoated walls, walls coated with the earth-sand mortar, and walls coated with the earth-brick waste mortar. The walls were subjected to a unidirectional heating cycle (10 ℃/min up to 800 ℃) to evaluate thermal stability and the capacity of the bedding and coating mortars to act as protective barriers. Thermocouples were used to monitor temperature evolution at different depths. After cooling, the uncoated walls showed vertical cracks and failure of the bedding mortars. For the coated walls, detachment was observed between the coating and the masonry, attributed to differences in the thermal expansion of the materials. The earth-sand coating showed cracks due to calcite decarbonation, reducing their efficiency. In contrast, the coating containing brick waste was free of cracks and showed better thermal stability. These results highlight the potential of earth-brick waste mortars to enhance the fire safety of bio-based earth masonry while providing a sustainable and innovative solution.