CONCRETE 



243 



If the sand is very fine, the pore space will be increased, 

 and therefore a little more cement will be required. The 

 materials should be mixed until they assume a uniform 

 color. If after thorough mixing the batch does not work 

 well, the sand and cement does not fill the spaces between 



FIG. 79. Concrete board and tools for making concrete. (Farmers' 

 Bulletin 461, U. S. Dept. Agr.) 



the stones, the proportion of stone should be reduced in 

 succeeding batches. 



TABLE XXV. QUANTITIES OF MATERIALS IN 1 CUBIC 

 FOOT OF CONCRETE 



