CEMENT FLOORS 283 



the sub-foundation and thoroughly rammed. The cement and sand 

 should be mixed dry until the mixture is of a uniform color, the gravel 

 or broken stone is then added, having previously been wet down, and 

 the concrete is thoroughly mixed, sufficient water being added during 

 the process of mixing to make a moderately wet concrete. The con- 

 crete is of the proper consistency if the moisture will just flush to the 

 top when the concrete is thoroughly rammed. The concrete should be 

 mixed until the ingredients are thoroughly incorporated and" each par- 

 ticle of the aggregate is thoroughly coated with mortar. 



The wearing coat is usually made of I part Portland cement and 

 one or two parts of clean sharp sand or granite screenings that will pass 

 through a ^4 -inch screen. The thickness of the wearing coat will de- 

 pend upon the wear, and varies from J^ to 2 inches thick, I inch being 

 a very common thickness. The mortar for the wearing surface should 

 be rather dry and should be applied before the cement in the concrete 

 base has begun to set. Care should be used to see that there is not a 

 layer of water on the upper surface of the base or that a film of clay 

 washed out of the sand or gravel has not been deposited on the sur- 

 face, for either will make a line of separation between the base and the 

 wearing surface. The mortar is brought to a uniform surface with a 

 straight edge, and is rubbed and compressed with a float to expel the 

 water and air bubbles. As the cement sets it is rubbed smooth with a 

 plastering trowel. Joints should be formed in the floor making it into 

 blocks about 4 to 8 feet square. 



Cement floors are said to be a failure for railway round houses for 

 the reason that they flake and crack after they have been used a short 

 time, on account of the varying changes to which they are subjected. 



Cement floors vary in cost, depending upon the thickness of the 

 floor and upon local conditions. In central Illinois a cement floor hav- 

 ing a i -inch surface coat and 3 inches of concrete laid on a cinder 

 foundation 6 to 8 inches thick can be obtained (1903) for about 12 

 cents per square foot. A very substantial concrete floor can usually 

 be obtained for about 20 cents per square foot. 



