The article concerns the possibility of obtaining modified cement mortars and assessment of their selected properties, i.e. bending and compressive strength, volume density of hardened mortars and water absorption. The modification consisted in a partial (0-50% vol.) substitution of sand by waste, crushed rubber, and cork. In the mortar design process, the theory of the experiment was used. The central composite design used available in the Statistica program was response surface. This approach has allowed to significantly reduce the number of experiments, reduce costs, and at the same time keep the maximum information about the mortars tested. The conducted research has shown that waste materials can be an alternative to natural aggregates in the process of obtaining light mortars.