SAND AND CEMENT 



203 



attacked by frost. Dry mortars, on the other hand, are 

 often friable and porous. 



In the following table are given the quantities of materials 

 required to produce 1 cu. yd. of compacted mortar. The 

 proportions are by volume, a cement barrel being assumed 

 to contain 3.6 cu. ft. 



MATERIALS REQUIRED PER CUBIC YARD OF MORTAR 



EXAMPLE. How much cement and sand will be required 

 to obtain 8.5 cu. yd. of 1-3 Portland-cement mortar? 



SOLUTION. According to the table, 1 cu. yd. of a 1-3 Port- 

 land-cement mortar requires 2.42 bbl. of cement; therefore, 

 8.5 cu. yd. will require 8.5X2.42 = 20.57 bbl. of cement. 

 Also, since 1 cu. yd. of a mixture of this kind requires 1.01 cu. 

 yd. of sand, the quantity of sand required will be 8.5X1.01 

 = 8.59 cu. yd. 



Mortar that is to be mixed by hand is prepared on a plat- 

 form or in a mortar box. The sand is first measured by 

 means of a bottomless box with handles on the sides. After 

 filling the box, the sand is struck off level, the box lifted up, 

 and the sand spread in a low, flat pile. The required num- 

 ber of bags of cement are then emptied on the sand and 

 spread evenly over it. The pile is then mixed with shovels, 

 working through it not less than four times. After this 

 operation, the dry mixture is formed into a ring, or crater, 

 and the water intended to be used is poured into the center. 

 The material from the sides of the basin is then shoveled 



