152 ADVANTAGES OF CONCRETE ON FARMS 



pebbles larger than those passing a one inch ring should 

 not be used. 



In the selection of sand the greatest care should be 

 used, and critical attention should be given to its quality, 

 for sand contributes from one-third to one-half of the 

 amount of the materials used in making concrete. Sand 

 may be considered as including all grains and small peb- 

 bles that will pass through a wire screen with one-fourth 

 inch meshes, while gravel in general is the pebbles and 

 stones retained upon such a screen. The sand should be 

 clean, coarse, and, if possible, free from loam, clay and 

 vegetable matter. 



In mixing materials for concrete use two and a half 

 times as much sand as Portland cement, and twice as 

 much gravel or stone as sand — that is, one part cement, 

 two and a half parts sand and five parts gravel or 

 crushed stone. Use just enough water to get the consist- 

 ency desired. If the sand is very fine the cement should 

 be increased from 10 to 15 per cent. When the mixture 

 does not have a uniform color, but looks streaky, it has 

 not been fully mixed. 



If the mixture does not work well and the sand and 

 cement do not fill the voids in the stone, the percentage 

 of stone should be reduced slightly, but the concrete 

 should first be properly mixed. Concrete that is poorly 

 mixed may present features that are entirely eliminated 

 by turning it over once or twice more. 



Concrete wet enough to be mushy and run off a shovel 

 when being handled is used for reinforced work, thin 

 walls, or other thin sections. Concrete just wet enough 

 to make it jellylike is used for some reinforced work and 

 also for foundations, floors, etc. It requires ramming 

 with a tamper to remove air bubbles and to fill voids. 

 This concrete is of a medium consistency. 



Sometimes bank or creek gravel, which will answer 

 the purpose of sand and gravel combined, can be ob- 



