Firing the wall: A novel way to protect earth buildings

Abstract

It is widely recognized that external earthen renders are susceptible to accelerated degradation caused by environmental factors. Therefore, chemical stabilization has become a common approach to address this issue. This study focuses on the stabilization of earth renders by heat treatment, considering criteria such as energy efficiency and the judicious use of resources. Different earth rendering mortars with additives such as wheat paste and horse dung were investigated. These were subjected to surface heat treatment at 400°C for one minute. Changes in mechanical properties, including shear strength, adhesion, and water erosion resistance were examined. The results showed that surface heat treatment at 400°C improved water erosion resistance but negatively affected shear strength and adhesion to the adobe substrate. Interestingly, the mortar containing wheat paste showed the least reduction in shear strength and adhesion, with a 16% decrease, while it experienced increased water erosion resistance. The phenomenon was observed in all specimens and is attributed to the microstructural changes induced by the irreversible processes of dehydration and dehydroxylation, which alter the clay components on the surface of the earthen render. Overall, heat treatment shows promise for improving the durability of earthen renders against environmental degradation.