The rheology of mixtures of fly ash-slag geopolymers, optimized for strength is not favorable for printing. Rheology modification is required using additives, which provide specific improvements in yield stress and thixotropy. These binders typically exhibit a pseudo-yield type behavior with a continuously deformable response under applied stress. A printable (both extrudable and buildable) material requires a yield-type behavior and adequate thixotropy, which can be brought out by addition of clay and Carboxymethyl Cellulose (CMC). The modification in rheology is attempted using commonly available Kaolinite clay. Specific changes in rheology caused due to the rheology modifiers are evaluated and are related with the performance in printing. Addition of clay contributes to an increase in the stiffness of the paste and improves buildability of the mix. A synergy between clay and CMC is established for proper printability. Clay in combination with CMC increases the storage modulus and produces a yield type behavior. CMC improves flocculation of clay but delays buildup due to its negative influence on reaction kinetics. Excess CMC increases the resistance to flow and produces a continuously deformable Maxwell response, which is not suitable for buildability. © 2022, The Author(s), under exclusive license to Springer Nature Switzerland AG.