The aim of this research is the maximum use of waste as a substitute for primary sources in cement mortars. In the experimental work, recycled concrete and waste mineral fibers were used to substitute the filler. Effects of different aggregate replacement ratios (5, 15, and 25%) on the resulting mortar properties were investigated. The application of waste materials resulted in a decrease in compressive and tensile strengths; on the contrary, a very favorable effect was recorded when monitoring the thermal insulation properties and frost resistance. The results of experimental work have shown that the waste materials used can be a full-fledged alternative to natural aggregates.