This term includes all those brick which are intended simply for constructional purposes, and with which no especial pains are taken in their manufacture. There are three grades of common brick, determined by their position in the kiln.
Arch or hard brick are those just over the arch, and which, being near the fire, are usually heated to a high temperature and often vitrified. They are very hard, and if not too brittle are the strongest brick in the kiln. They are often badly warped, so that they can only be used for footings and in the interior of walls and piers.
Red or well-burned brick should constitute about half the brick in the ordinary up-draft kiln, and when made of clay containing iron should be of a bright red color. For general purposes they constitute the best brick in the kiln.
Salmon or soft brick are those which form the top of the kiln and are usually underburned. They are too soft for heavy work or for piers, though they may be used for filling in light walls and for lining chimneys.
The strength and hardness of common bricks of all grades vary greatly with the locality in which they are made on account of the difference in the clay. Some of the salmon brick of New England are fully as hard and strong as the red bricks of other localities, particularly in the West. As the color of a brick may be due more to the presence or absence of iron than to the burning, it cannot be used as an absolute guide to the quality of the brick.
Stock brick are a handmade brick intended for face work, and with which greater care is taken in the manufacture and burning than with common brick. In the East they are sometimes called face brick.
Pressed brick or face brick generally refers to brick that are made in a dry press machine, or that have been repressed. They are usually very hard and smooth, with sharp angles and corners and true surfaces; they may be either stronger or weaker than common brick, according to the character of the clay and the degree to which they are burnt. Pressed brick are not usually burnt as hard as common brick, and are, therefore, sometimes not as durable. Pressed brick cost from two to five times as much as common brick, and are, therefore, generally used only for the facing of the wall.
Moulded, arch and circle brick are special forms of pressed brick. A great variety of moulded or ornamental bricks are now made, by means of which mouldings and cornices may be built entirely of brick. Most of the companies manufacturing pressed bricks will also make any special shape of brick from an architect's designs. Arch bricks are made in the form of a truncated wedge and are used for the facing of brick arches. They can be made for any radius desired. Circle brick are made for facing the walls of circular towers, bays, etc. The radius of the bay should be given when ordering these brick.