The high consumption of non-renewable resources coupled with the generation of solid waste has been contributing to the search for sustainable materials that can be used in civil construction. Brewer´s spent grain is a by-product generated from the beer production process, formed by the solid part obtained from the wort filtration, before boiling. It is the main by-product of the brewing process and is currently destined for animal feed. The declared beer production volume in Brazil reaches 15.3 billion liters, which represents approximately 3.06 million tons of spent grain. Coating mortars with spent grain in their composition emerge as an alternative to minimize the environmental impact associated with the presence of Portland cement and lime, while improving their hygrothermal properties. Due to its cellular structures, malt bagasse has a high water absorption capacity, which can be used to improve the water retention capacity of the mortar, working as a functional substitute for lime. Thus, this study proposes the development of a coating mortar containing malt bagasse as partial replacement of lime in cement:lime:sand matrices. Mortars with volume substitutions of lime by malt bagasse of 5, 10 and 15% were produced and tested in fresh and hardened state. Results indicate that the direct substitution of lime by malt bagasse led to a decrease in workability, an increase in entrapped air and a decrease in compressive strength. It was concluded that for the proper application of the material, the water absorption capacity of the bagasse must be taken into account during proportioning. The feasibility analysis of using spent grain for the production of cement composites represents an important step towards sustainability in civil construction, offering an innovative and environmentally responsible solution for the use of agro-industrial waste and the reduction of the environmental impact of the construction industry.