Glass fiber reinforced polymer (GFRP) recycled from retired wind turbines was implemented in mortar as a volumetric replacement of sand during the two phases of this study. In Phase I, the mechanically refined GFRP particle sizes were sieved for four size groups to find the optimum size. In Phase II, the select GFRP size group was incorporated at three different volumetric replacements of sand to identify the optimum replacement content. The mixtures were tested for compressive strength, flexural strength, toughness, and the potential for alkali-silicate reaction. Incorporation of GFRP in mortar proves promising in improving flexural strength and toughness in fiber-like shapes and 1–3% volumetric fractions.