The present contribution focused mainly on the fundamental understanding of the influence of surface-modified graphite on rheology of the matrix of a castable slurry in comparison to the same containing the uncoated one. A special observation on the rheology of a graphite-free matrix of similar high alumina castable has been described. The change in rheological behavior due to the presence of other microfine constituents has also been noticed with a particular attention to the refractory cement bond. The variation in viscosity and shear stresses with shear rate of castable matrices containing as-received and surface-modified graphites has been compared. The ‘ball-in-hand’ consistency test of respective castables had also been differentiated. The effect of coated and uncoated graphites on the loss and storage moduli of the respective suspensions has been explored. Zeta potential values of individual constituents as well as the slurries have also been measured and correlated with the flow characteristics of castable matrices. The X-ray diffraction (XRD), SEM (scanning electron microscope) and EDS (energy dispersive spectroscopy) studies of the coated graphite have been observed to substantiate the flow pattern of the slurry. The physical properties of refractory castables at different temperatures have been estimated to supplement the rheological pattern. © 2019 Elsevier Ltd and Techna Group S.r.l.