In order to prevent the penetration of moisture the mason should butter all joints on the inside and outside edges, leaving an empty space between, in order to insulate against the transmission of moisture through the joint. To prevent the collection of mortar in the cells of the tile, due to droppings during construction, the spreading of metal lath over the top of each course of tile will accomplish this and also make the strength of the wall greater. Although it is often recommended that hollow tile be plastered directly upon the interior, yet this is not safe in those sections of the country where there are driving rain-storms. For this reason it is advisable to fur them on the interior. It is also recommended that a waterproofing compound be added to the stucco applied to the exterior. Another fact should be observed: namely, that all door and window frames, since they are of wood, will tend to shrink and thus open up the joints and permit the leakage of rainwater. Oakum should be stuffed behind all brick moulds to prevent this. Care should also be taken to make drips under all sills, so that no water will leak into the interior of the wall. All belt courses should also have steep washes. Stucco should not be carried down to the grade level, but a course of solid material, like brick, concrete, or stone, should be built at this point.