"When neat Portland cement is used in thin layers that are exposed to the air, it cracks and breaks off. Thus it is unfitted for skimming walls or floors, or for pointing brickwork, and in such eases should be mixed with sand in the proportion of 1 of cement to 1 of sand, or 2 of cement to 1 of sand. Cement may be used neat for jointing-drain pipes when the drains are to be filled in quickly, but in most cases the question of expense will prevent neat cement being used for this purpose. The cause of the cracking, and of the brittleness, is attributed to unequal shrinking. Where the cement will not be exposed to air, as in the interior of brickwork, it may be used neat if necessary.