152 



ENGINEERING ON THE FARM 



strength of the same mixture, when fifty days of age, is 

 approximately 2,000 pounds, as a factor of safety of 

 approximately 3 is considered necessary. A 1:3:6 mixture 

 would safely carry 500 pounds per square inch, while the 

 same mixture at fifty days of age would require 1,600 



Fig. 147. A group of cement finishing tools 



pounds to crush it. The strength of reinforced concrete 

 depends upon the quantity of steel used and the area of 

 the cross sections. 



FINISH 



Trowel finish. When freshly poured concrete is rubbed 

 with a metal trowel, the sand is forced down and the cement 

 brought to the surface, which gives it a smooth, glossy 

 appearance known as a trowel finish. (See Fig. 148.) 



Float finish. If freshly poured concrete is rubbed with 

 a piece of wood or soft material when quite wet, the sand 

 is brought to the surface and presents a rough or grainy 

 surface known as a float finish. While the float finish is 

 not so pleasing to the eye as the trowel finish, it is not so 



