Grouting is widely used in the treatment works of goaf, which can enhance the foundation bearing capacity, reduce deformation, and ensure the stability of the construction of goaf. As the goaf is located below the water table line, the mechanical properties and microscopic changes of the stone body in the water-rich environment have not been revealed, which leads to the effect of grouting treatment in water-rich goaf being difficult to achieve in terms of the expected goal. This paper used uniaxial compression, electron microscopy (SEM), and X-ray diffraction (XRD) to study the mechanical properties and microscopic changes of the nodular body under natural, pure water, and tap water curing and revealed the deterioration mechanism of the nodular body’s mechanical properties under water curing. The research results show that under identical material proportions and curing durations, compared to naturally cured specimens, the specimens cured in purified water and tap water exhibited a significant increase in the content of unreacted fly ash, a reduction in the amount of hydration products such as C-S-H gel and ettringite, and a looser microstructure, resulting in average decreases in uniaxial compressive strength of 35.7% and 49.9%, respectively. In addition, the presence of chloride ions and Friedel’s induced decalcification of the C-S-H gel under tap water curing conditions led to a significant deterioration in the physical strength of the grouted stones.