306 MASONRY 



Requisites for Good Brick. Bricks of good quality should 

 be of regular shape, with parallel surfaces, plane faces, and 

 sharp square edges. They should be of uniform texture; 

 burnt hard; and thoroughly sound, free from cracks and flaws. 

 They should emit a clear ringing sound when struck a sharp 

 blow. A hard well-burned brick should not absorb more than 

 one-tenth of its weight of water; it should have a specific 

 gravity of 2 or more. The crushing strength of a brick laid flat 

 should be at least 6,000 Ib. per sq. in. The modulus of rupture 

 should be at least 1,000 Ib. per sq. in. 



CEMENTING MATERIALS 



Lime. Common lime, commercially called quicklime, is 

 manufactured by calcining, or burning, at a temperature of 

 from 1,400 to 2,000 P., stones composed of pure or very 

 nearly pure carbonate of lime. The product is practically 

 pure oxide of calcium. It is prepared for use, converting it 

 into calcium hydrate, by the addition of water. This process 

 is called slaking. The quantity of water required in slaking 

 lime is about one-third the volume of the lime. 



Lime weighs about 66 Ib. per bu., or about 53 Ib. per cu. ft. 

 One barrel of lime, weighing 230 Ib., will make about 2J bbl., 

 or .3 cu. yd. of stiff paste. In l-to-3 mortar, 1 bbl. of unslaked 

 lime will make about 6f bbl. of mortar; or 1 bbl. of lime 

 paste will make about 3 bbl. of mortar. For a l-to-2 mor- 

 tar, use is made of about 1 bbl. of quicklime to 5 or 5 J bbl. of 

 sand. 



Hydraulic Cements. The hydraulic cements are divided 

 into three main classes; namely, Portland cement, natural 

 cement, and pozzuolana. These cements differ from the limes 

 by not slaking after calcination. 



Portland cement is the product resulting from the process 

 of grinding an intimate mixture of calcareous (containing lime) 

 and argillaceous (containing clay) materials, calcining (heating) 

 the mixture until it starts to fuse, or melt, and grinding the 

 resulting clinker to a fine powder. 



Natural cement is made by calcining natural argillaceous or 

 silicious limestones at a heat just below fusion and grinding 

 the product to powder. 



