204 



SAND AND CEMENT 



into the center until the water is entirely absorbed, after 

 which the pile is worked again with shovels and hoes until 

 the mixture is uniform and in a plastic condition. 



Another method of mixing, where a mortar box is used, 

 is to gather the mixed dry materials at one end of the box 

 and pour in the water at the other end drawing the mixture 

 into the water with a hoe, a little at a time, and hoeing until 

 a plastic consistency is obtained. 



Properties and Uses of Cement Mortars. The strength of 

 a mortar is measured by its resistance to tensile, compressive, 



TENSILE STRENGTH OF CEMENT MORTARS 



cross-breaking, and shearing stresses, and also by determi- 

 nations of its adhesion to inert surfaces, its resistance to 

 impact, abrasion, etc. There is no definitely fixed ratio 

 between the strength of mortar subjected to these different 

 stresses, but there is nevertheless a close relation between 

 them, so that, practically, it may be assumed that if a mor- 

 tar shows either abnormally high or low values in any one 

 test, the same relation will develop when tested under other 

 stresses. In practice, therefore, the strength of mortar is 



