,? committee of engineers and architects recommended to the City of Chicago in l90' , the following values 10 lie used as safe working pressures for brick masonry in building tcns1e1c1ion: The building code of the City of St. Louis, in 1917, gives the following allowable compression on brick masonry: Per sq. in.
Vitrified paving brick, one part Portland cement, three parts sand 300 Strictly hard pressed brick, one part Portland cement., three parts sand 250 Ordinary hard and red brick, one part Portland cement, three parts sand 200 Ordinary hard and rad brick, one part Portland cement, one line, three sand 175 Merchantable brick, good liine mortar 100 Vitrified paving brick and strictly hard brick shall not crush at less than five thousand (5000) pounds pressure per square inch. Ordinary hard and red brick shall not crush at less than two thousand and three hundred (2300) pounds pressure per square inch. Merchantable brick shall not crush at less than one thousand and tight hundred (1800) pounds pressure per square inch, 63. Effiorescence.—The appearance of brick masonry is sometimes marred by a white coating which exudes from the masonry and is deposited upon its surface. This is called efflorescence, and is caused by soluble salts in the brick or the mortar, usually the latter, which are dissolved by water when the wall is wet and deposited on the surface as the water evaporates. Such deposits usually consist of salts of soda, potash, or magnesia contained in the lime or cement, or of sulphate of lime or magnesia from the brick.
Efflorescence may be prevented by keeping the wall dry. The use of impervious materials, and making the masonry itself imperme able, render the appearance of efflorescence improbable. When a wall is in a clamp situation, a clamp-proof course at the base of the wall to prevent moisture rising in the masonry is desirable. If the masonry is permeable and is dampened by rain, some waterproof coating may be applied to the surface of the wall. There are various patented preparations for this purpose, and the Sylvester process is sometimes successfully used. This consists in applying first a wash of aluminum sulphate (1 pound to 1 gallon of water), and then a soap solution (2.2 pounds of hard soap per gallon of water). These
applications are made twenty-four hours apart. The soap solution is applied at boiling temperature. The walls must be dry and clean, and the air temperature should not be below about 50° F. when the application is made.
Efflorescence may usually be removed by scrubbing with a weak solution of hydrochloric acid.
64. Measurement and Cost.—Measurement of brickwork is usually made by estimating the number of thousand bricks. It is assumed that an 8- or 9-inch wall contains 15 bricks per square foot of surface; a 13-inch wall, 22i bricks; a 17- or 18-inch wall, 30 bricks, etc. These numbers arc employed without regard to the actual size of the bricks, adjustments in price per thousand being made for various sizes.
The methods of estimating are sometimes rather complicated and are subject to rules established by custom. The plain wall is the standard of measurement, openings less than 80 square feet are usually not deducted; larger openings are measured 2 feet less in width than they actually are. Hollow walls and chimneys are measured solid.
A pier is sometimes measured as a wall whose length is the cir cumference and whose thickness is the width of the pier. Some times one-half the circumference is taken as the length.
Stone trimmings are not deducted from the brickwork measure ments. Various rather complicated rules are used in estimating footings, pilasters, detached chimneys, etc.
Having estimated the work in thousands of brick by these rules, a price per thousand, suited to the plain is used for the entire job. When pressed brick facing is used, the area of such facing is separately estimated. If an ashlar facing be used, its thickness is not included in that of the brick wall.
It. engineering work, brickwork is usually measured, like stone masonry, by the cubic yard of actual masonry.
Number of Bricks licquired.—The actual number of bricks needed for the construction of masonry varies with the size of the bricks and the thickness of joints. For ordinary brickwork, with common bricks of the usual (S; X 1 X21 inches) size, and joints to inch thick, 1000 bricks \Vial lay about 2 cubic yards of masonry. If the joints be to inch thick, 1000 bricks will lay about 22 cubic yards.