Described are admixture composition and method for integrally waterproofing cementitious compositions, such as concrete and mortar, wherein an organosilicon compound (e.g., silane) is mixed with animal oil, vegetable oil, or mixture thereof, and defoaming agent. The organosilicon/oil mixtures of the present invention enhances the water repellent efficacy of the organosilicon, even as it displays inherently greater product stability, as compared to emulsion-based (and thus substantial free-water containing) admixture formulations of the prior art. Cementitious materials made in accordance with the present invention demonstrate excellent air consistency and air neutrality.