A good way to think of this is cement is to concrete as flour is to a cake. Cement is only one of the constituents of concrete and mortar. The various basic mixes can be defined as: Mortar – cement, fine aggregate (sand) and water. Concrete – cement, course aggregate (generally 10-20mm rocks), fine aggregate (sand) and water. These can also contain various additives (such as lime) and admixtures (such as a waterproofer).