Control over the flowability of cement mortar in the two-stage concreting method is crucial for ensuring the desired performance and durability of the final concrete structure. Thus, a comprehensive study using an advanced vane-type coaxial rheometer, which precisely measures the material’s flow characteristics, is essential alongside regular flow cone measurements. In this study, TSC cement mortar was mixed with varying amounts of silica fume (SF) and superplasticizer (SPs) to investigate their impact on rheological properties. The results indicated that adding SF increased the viscosity and yield stress while adding SPs reduced these properties. The variations emphasize the significance of meticulous selection and proportioning of supplementary cementitious materials (SCMs) and admixtures to attain the desired rheological properties of cement mortar. Refining the mixture using the insights obtained from this study makes it feasible to improve the workability, strength, and durability of the concrete, ultimately leading to more efficient construction practices.