An additive composition, a cement composition, and method for modifying rheology of an uncured masonry cement, comprising the use of at least one extra-cellular biopolymer, at least one anionic surfactant, and at least one cationic or amphoteric surfactant. Preferably, the biopolymer and surfactants are incorporated into the cement by incorporating the components into the grinding of clinker as part of the manufacture of the cement. Masonry cements produced by the invention have excellent workability, particularly when coarse sands are employed.