The main objective of this contribution is the study of mortars with the incorporation of polymer-based phase change materials (PCM) for the improvement of energy efficiency in buildings. The mortars are intended for an indoor thermal comfort in the typical climatice conditions of the Southern European countries. Production waste, such as stone powder from quarry, will also be incorporated in the mortars. The finer powder is proposed as mortar aggegate and, at the same time, as support for the PCM. Firstly, different procedures aimed at effectively introducing the selected polymeric material (PEG) into the Lecce stone have been performed. The chemical and thermal characterization of these compounds has been carried out. The LS/PEG composites have been, then, added to a mortar. Experimentsare in progress in order to characterize from chemical, physical, and thermal poit of view the mortars with and without PCM, following the recommendations of the international standards in this field. In addition, the studied materials will be used to build laboratory-scale prototypes taht will be tested in real environmental conditions.