In recent years, the environmental facet of industrial waste management has become imperative. The recycling of these residues in the civil construction sector is growing, since both industries have developed an increasing concern for the exhaustion of natural resources. In this scenario, one example is the ladle furnace slag (LFS), a by-product of the secondary refining of steel. It is mainly composed of calcium and calcium magnesium silicates. Thus, this research aims to develop a sustainable binder obtained from LFS as a substitution of hydraulic lime. In this sense, an extensive characterization of the LFS was carried out in its raw and processed forms. Subsequently, all the requirements for hydrated lime and hydraulic lime were verified according to Brazilian and Portuguese standards. Finally, mortars for coating and laying were produced with portland cement, lime, and the sustainable binder, and their main properties were evaluated in the fresh and hardened states. The chemical and mechanical properties of the sustainable binder were closer to those of the hydraulic limes. The obtained results indicate the technical feasibility of the use of LFS as binder for mortars in the replacement of lime.