The incorporation of rubber aggregates from tire wastes into mortar is a way to reach new properties of materials based on Portland cements and to generate alternatives for the mechanical recycling of tire rubber waste. However, the rubber aggregates present distinct chemical characteristics when compared to the others mortar components, leading to a low interface interaction between the rubber and the cementitious matrix and consequent reduction of mechanical properties of the material. Thus, the aim of this study was to evaluate the compatibilization in rubberized mortar, using unsaturated polyester resin as coupling agent to cover the rubber particles and chemically bond them to the others mortar components. The compatibilization methods employing the adhesion systems rubber–sand, rubber–cement and rubber–sand–cement were analysed and the compatibilized materials were characterized by mechanical test and scanning electron microscopy. The compatibilization caused positive changes in the rubberized mortar, generating perspectives for development and application of the material.