CONCRETE 245 



and outside, amounting in all to 400 square yards of surface, 

 with a 1 : 1 mixture of sand and cement. One cubic foot 

 of 1 : 1 mortar paints about 15 square yards of surface and 

 requires 0.1856 barrel of cement and 0.0263 cubic yard 

 of sand. The problem thus works out as follows: 



Cement: Barrels. 



For the 750 cubic feet of 1 : 2 : 4 concrete (750X0.058) ... 43.5 

 For the 185 cubic feet of 1 : 2J : 5 concrete (185X0.048) . . 8.9 

 For painting (400 -=-15X0.1856) 4.9 



Total amount of cement. . . 57 . 3 



Sand: Cubic Yds. 



For 750 cubic feet of 1 : 2 : 4 concrete (750X0.0163) 12.23 



For 185 cubic feet of 1 : 2| : 5 concrete (185X0.0176) 3.26 



For painting (400-7-15X0.0263) 70 



Total amount of sand. . . 16. 19 



Stone or gravel: 



For 750 cubic feet of 1 : 2 : 4 concrete (750X0.0326) 24.5 



For 185 cubic feet of 1 : 2 : 5 concrete (185X0.0352) ' 6.5 



Total amount of stone or gravel 31.0 



v 



Thus the necessary quantities of materials are about 

 57| barrels of Portland cement, about 16| cubic yards of 

 sand, and 31 cubic yards of stone or gravel. 



193. Mixing Concrete. In mixing concrete the sand is 

 first spread over the mixing floor in a layer 3 or 4 inches in 

 depth. The cement is then spread evenly over the sand. 

 These materials are then mixed thoroughly with a shovel, 

 the mixture is spread over the floor and the gravel is added. 

 About three-fourths of the water to be used is then thrown 

 as evenly as possible over the gravel layer and the materials 

 are again thoroughly mixed with the shovel. Water should 

 be added to the dry spots as the mixing proceeds, until 

 the full amount has been used. After thoroughly mixing, 

 the concrete is shoveled into a compact pile. 



