When cement is mixed with sand and water, the resulting paste is called mortar. The term "neat cement mortar" is sometimes used to designate a cement paste without sand, but when the term mortar is not qualified, it refers to the mixture containing sand. The primary function of mortar is to bind together pieces of stone of greater or less size, though it is sometimes used alone to prevent the percolation of water, to make a smooth exterior finish, or in places too confined to permit of placing concrete.
There are comparatively few cases in which it is judicious to use cement without the addition of sand, for such an admixture not only cheapens the mortar, but actually improves it for nearly all purposes. The quality of sand used is only second in importance to the quality of the cement. Indeed, if one does not know how to select either a good cement or a good sand, he is in greater danger of going amiss in the selection of the latter than the former; for the cement has been placed upon the market by a manufacturer who has a reputation to establish or maintain.