This section is from the book "A Treatise On Architecture And Building Construction Vol2: Masonry. Carpentry. Joinery", by The Colliery Engineer Co. Also available from Amazon: A Treatise On Architecture And Building Construction.
Common Brick. The term common brick includes all those that are intended for constructional, and not for ornamental purposes, and have no special pains taken in their manufacture. There are three grades of common brick, termed according to their position in the kiln, arch or hard brick, red or well burned brick, and soft or salmon brick.
171. Stock brick are a hand-made brick intended for face work; greater care has been taken in the manufacture and burning than with common brick. They are used extensively for the outside facing of factories, machine shops, and the cheaper class of private dwellings. In the Eastern states they are sometimes called face brick.
Pressed Brick Or Face Brick. These are the brick 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 sides and beds. They cost from two to five times as much as common brick, and are, therefore, usually laid only in the face of the wall.
Special forms of pressed brick are called molded, gauged, arch, and circle brick. Molded and ornamental brick are now made in a great variety of forms and patterns, so that cornices and moldings may be made entirely of brick.
If the architect requires special patterns of molded brick to carry out his designs, most of the larger companies manufacturing pressed brick will make the special shapes so desired, if drawings are furnished. These should be drawn to a large scale, and full-sized details should be given.
The walls of circular towers, bay windows, etc. are faced with what are known as circle brick, or brick molded to the shape of the circle desired.
The radius of the bay or tower should always be given when ordering either kind.
Firebrick. These brick are used for the lining of furnaces, lime kilns, fireplaces, and tall chimneys in manufactories. They should be free from cracks, of homogeneous composition and texture, uniform in size, of a regular shape, easily cut, and not fusible. They are usually somewhat larger than the ordinary building brick.
Firebrick are made from a mixture of about 50 per cent. raw flint clay and 50 per cent. plaster clay. The brick are made by the stiff-mud and dry-press processes, and by the soft-mud process, hand molded. It is generally thought that the last process gives the most perfect brick.
175. Glazed and enameled brick are used largely for lining water-closet and bathroom walls, the wainscoting of halls and staircases, and in many cases for the entire walls of stores and restaurants, hospitals, public waiting rooms, and markets, or wherever a non-absorbent surface that is clean and light is desired. They can be used for external as well as for internal purposes, as they will stand the most severe changes of weather, reflect light, acquire no odor, are impervious to moisture, and are fireproof.
176. The term enameled is given to all bricks having a glazed surface. There exists, however, quite a marked difference between a glazed brick and an enameled brick. 2-7
A genuine enameled brick has the enamel fused into the brick without any intermediate coating, and the enamel is opaque in itself. The glaze, on the contrary, is produced by first covering the unburned brick with a "slip," as it is called, and then with a second coat of a transparent glaze closely resembling glass.
The enameled surface can be distinguished from one that is merely glazed by chipping off a piece of the brick. The enameled brick will show no line of demarcation between the body of the brick and the enamel, while the glazed brick will show a layer of slip between the glaze and the brick. The bricks are enameled or glazed only on one face or on one face and one end.
The true enameled brick costs more than the glazed brick, as it is more difficult to manufacture; but, owing to the enamel being a part of the brick itself, an enameled brick is more desirable than a glazed brick, and will not chip or peel as readily.
177. The slip used in the manufacture of glazed bricks is a composition of ball clay, pulverized kaolin, flint, and feldspar. The unburned brick is first coated on the side to be glazed with this composition, which adheres to and covers the clay, and also receives and holds the glaze, which is put on very thin. After burning, the glaze leaves a transparent body covering the white slip.
178. The real enameled brick are made from a certain kind of clay that usually contains a considerable quantity of fireclay. The enamel is applied either to the unburned brick or after it is burned. It is claimed that the latter method produces the best brick.
After the enamel is applied, the brick is burned and the enamel fuses and unites with the brick in the same manner that the glaze on a teacup or saucer unites with the material composing the cup or saucer. It is not transparent and shows its own color.
For many years all the glazed and enameled brick were made in England, but there are now several factories in this country. The English brick are 3 inches X 9 inches X 4 1/2 inches. Most of the American factories make the American standard size, which is 8 1/4 inches X 4 inches X 2 1/4 inches, but some of them adhere to the English standard.
179. Paving brick do not come strictly within the province of the architect, but, as he may have occasion to use them for paving driveways, etc., it is well to have some knowledge of them. These paving bricks are also used sometimes for paving the flat roofs of office buildings, apartment houses, etc., and when laid in cement make a durable fireproof roof covering.
It is usual to make paving brick by the stiff-clay process, and the brick, after being cut from the bar, are generally - although not always - repressed to give them a better shape. Shale clay and about 25 to 30 per cent. of fireclay are used in making paving brick. In order to stand frost and wear, paving brick require to be very hard, and therefore must be burned to vitrification, or until the particles of the body of the brick have been united in chemical com-bination by means of heat. Some varieties of paving brick are made without burning. They are manufactured by a process of intimately mixing materials of the nature of cement, and squeezing the mixture by hydraulic pressure. A serviceable paving brick is made from ground furnace slag, lime, etc. mixed with cement; when the cement is set, the brick is as hard as stone.
180. In order to enable paving brick to withstand the various sources of wear and disintegration to which they must be exposed, in a street or driveway, or even on a roof, they must be very compact in texture, and must have the qualities of vitrification and toughness, and should not be so distorted in shape as to lie unevenly in the pavement. This crushing strength should not be less than 8,000 pounds per square inch. Paving brick should absorb little or no water, and, when thoroughly vitrified, the limit of absorption should not be more than 4 per cent., and paving bricks are made that do not absorb more than 1 per cent. If the bricks absorb water, frost will soon crack- them, and they will quickly be destroyed.