Abstract: A masonry cement is prepared by dry mixing portland cement, diatomaceous earth and a water-swellable colloidal clay, such as bentonite. Accordingly, the crushed limestone and other ingredients previously included in masonry cements for admixture with portland cement can be completely eliminated and substituted by diatomacious earth and water-swellable colloidal clay. In this manner, a combination of less than about 10% by weight of a combination of diatomaceous earth and colloidal clay replaces approximately 50% by weight crushed limestone and other ingredients from prior art masonry cement compositions while providing a masonry cement which meets ASTM specifications, particularly for air entrainment, water retention and compressive strength.