Abstract <p>The efficiency of redispersible polymer powder, cellulose ether, and calcium formate additives for controlling the mechanical properties of cement composites was examined. The early strength of modified cement composite specimens was determined after 30–90 min of curing, and the curing kinetics were investigated using isothermal calorimetry. For the most promising specimens, the rheological characteristics of the fresh mix, strength properties at later curing ages (up to 28 days), and sample structure (analyzed by X‑ray computed tomography) were determined. Additions of redispersible polymer powder and calcium formate at a dosage of 2% by weight of cement contribute to improved compressive strength of the cement composites. Both additives increase specimen strength by 42–64% after 1 day and by 21–47% after 3 days. After 7 days, 2% calcium formate increases specimen strength by 32%, and after 28 days by 15%. The studied additives increase the viscosity and density of the mix; in addition, with 2% redispersible polymer powder the initial and final setting times are shortened by 15 min. The results indicate that the additives investigated can be regarded as efficient modifiers of cement composites suitable for additive construction technologies.</p>