Adsorbed polymer additives have been employed to reduce water content and improve cement workability through lowering viscosity, but the influence of over‐dosage and the presence of nonadsorbed chains have yet to be fully understood. Model magnesium oxide (MgO) suspensions were used to investigate the potential processing effect of “free” chain concentration on cementitious mixtures. The rheological impact of the free chains was measured through incorporation of nonadsorbing poly(ethylene glycol) (PEG) to suspensions stabilized with an adsorbed comb‐polymer superplasticizer. Analyses of the rheological data, that showed viscosity‐increases and viscosity‐reduction due to free PEG concentrations revealed a transition from depletion flocculation to depletion stabilization that contributed to the flow properties of the suspensions. The viscosity‐reduction observed for high concentrations of free chains may be useful for improved mixing of cements with free polymer in addition to the adsorbed polycarboxylate ether‐based superplasticizer. Additionally, the influence of free PEG on the macroscale flow behavior was also examined through local velocity measurements under shear. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018, 135, 45696.