The mortar used in these side walls is formed by mixing clean sharp sand with hydraulic lime, using the proportions of three parts of the sand to one of the lime ; and these are thoroughly mixed and incorporated before they are wet ; when this mixture is wet and thoroughly worked, it is used immediately and always kept properly tempered so as to render it plastic, and to prevent any disposition to become hardened before it is in the wall. After the side
walls are finished and the concrete between them has received its proper form, a coating of plastering, about three eighths of an inch in thickness, is put on over the surface of the concrete and on the face of the walls before the interior facing of brick is commenced. The proportions of this plastering are two parts of sand to one of the hydraulic lime. The bricks used in this work are generally of quite a different character from those used in ordinary house-building ; being harder burnt and of a superior quality of material. They are required to be burnt to such a degree of hardness that they present a cherry red, or brownish color, and give a clear ringing sound when struck ; and when broken, must present a compact and uniform texture. All bricks brought upon the work which are soft and of a pale color, such as are usually denominated salmon brick, are rejected. Those which are used, possess nearly the hardness and durability of ordinary building stone, and are calculated to resist the action of the water, to which they will be exposed.