CONCRETE CONSTRUCTION 249 



1000 x 0.058 or 58 barrels of cement 

 1000 x 0.163 or 16.3 cubic yards sand 

 1000 x 0.0326 or 32.6 cubic yards gravel 

 In estimating for cement mortar, figure i 

 cubic foot to each 15 square feet of surface to 

 be covered. Each cubic foot of i :i sand and 

 cement mortar requires 0.1856 barrels of ce- 

 ment and 0.0263 cubic yards of sand. 



Forms.^-As concrete is soft when mixed, 

 it is necessary to have some kind of a form 

 or, mold to hold it in the desired form and 

 position until it hardens. For foundations, 

 for such structures as greenhouses, a trench 

 is usually dug 12 or 14 inches wide, and deep 

 enough so that the bottom will be below 

 the frost line. If the soil is firm enough to 

 hold its place no form will be needed, but 

 the concrete may be poured directly into the 

 excavation, tamped and allowed to harden. 



For that part of the wall which is above 

 ground, however, a form is needed. It is 

 important that this form be vertical, that 

 it be straight, and that it be smooth in the 

 inside so that the resulting wall will be agree- 

 able to the eye. The making of the forms is 

 important. They should be built by an ex- 

 perienced carpenter. 



