A fresh aqueous cement composition suitable for building purposes is described. It contains, besides a hydraulic cement, a methyl ethyl cellulose ether having a DS methyl of 0.4-2.2, a DS ethyl of 0.05-0.8 and a MS hydroxy-(C.sub.2-C.sub.3)-alkyl of 0-2. The celulose ether imparts excellent rheology properties, including a high water-retention combined with a long open time, to the cement composition. A dry blend and a rheology additive containing the cellulose ether are also described.