This paper presents an experimental investigation into the use of waste recycled polyvinyl chloride (PVC) as an alternative fine aggregate in eco-friendly mortars. The aim is to improve the brittle behavior of cementitious materials in strong acid environments as well as the improvement of the thermal insulation performance of the developed material. Mortars incorporating 0, 10, 30, 50 and 70% PVC as a replacement for natural sand were studied. Density, compressive and flexural strengths, ultrasonic pulse velocity, and thermal conductivity tests were performed to evaluate the properties of PVC-mortar composites. The resistance of different mixes to strong acids was examined based on 5 weeks’ of immersion in 5% sulfuric acid (H2SO4), 5% hydrochloric acid (HCl), and 5% nitric acid (HNO3) solutions. The results showed that the incorporation of up to 70% PVC into lightweight ductile mortars is possible, though values of compressive and flexural strengths and ultrasonic pulse velocity decreased with increase in PVC content. In addition, the use of PVC aggregates by natural sand replacement caused the resistance of mortars against strong acids to increase considerably. Based on the thermal conductivity results, mortars with higher PVC aggregates rates improved the thermal insulation of composite mortars.