124 



CEMENT AND CONCRETE 



there is always a tendency to mix in small units, which is 

 sometimes a mistaken idea. It is usually best to mix at least 

 enough so that one sack of cement or one cubic foot can be 

 taken as a unit because, if the sack is emptied and only a 

 part of a sack is taken, the cement will fluff up and form 

 more than one cubic foot. 



119. Procedure in Hand-Mixing. In the actual process 

 of mixing, it is usually best to spread the sand on the mixing 



FIG. 138. Spreading cement on sand. 



board, and on top of this spread the sack of cement (Fig. 

 138); then two men using square-pointed shovels turn this 

 sand and cement over several times until the streaks of color 

 are merged into a uniform shade throughout the entire mass. 

 The coarse aggregate is then added (Fig. 138-a), and during 

 the first turning, water is added by means of a hose or from a 

 bucket (Fig. 139). Care must be observed to prevent wash- 

 ing the cement out of the mass. It is best to turn the mate- 

 rials several times (Fig. 139-a), adding a small amount of water 



