C erne lit for the Farm. 413 



Crete materials is 1, trap; 2, granite; 3, gravel; 4, marble; 5, limestone; 

 6, slag; 7, sandstone; 8, slate; 9, shale ; 10, cinders. 



For thin walls or in reinforced work, the size of the particles 

 (rock or gravel), in the aggregate shonld not exceed one (1) inch — 

 from 1/4 to 1 inch is a good regulation, depending somewhat upon con- 

 ditions. For concrete, where mass or weight, such as heavy founda- 

 tions, dams, retaining walls, etc., are desired, pieces up to 2 or 3 inches 

 on the greatest dimension may be used. Stone 6 to 12 inches across 

 may be embedded in plain concrete for very heavy foundations or 

 walls — these pieces thrown bodily into the concrete is termed a "one- 

 man" concrete. They must be completely embedded in the concrete. 



The weight of gravel or limestone, broken to concrete size, is 

 approximately 2,500 pounds per cubic yard. The voids in gravel are 

 from 35 to 45 per cent; in broken limestone, screened, 48 to 50 per 

 cent ; limestone, crusher run, 40 per cent. 



Mixing — All ingredients, cement, sand, rock and water should be 

 practically clean. The cement and sand should first be thoroughly 

 mixed dry upon a suitable and water-tight platform and the stone 

 or gravel then added. In dry hot weather, the broken stone or 

 gravel should be dampened before being added. When the mortar is 

 prepared the stone is spread upon it and the whole turned with shovels 

 at least three (3) times — and worked rapidly. A sufficient amount of 

 water is added before and during the mixing to produce the proper 

 consistency. 



Enough water is required to make a pasty mixture. Keinforced 

 concrete requires a wetter mix than plain concrete. A wet mix, not 

 sloppy, for many kinds of concrete, is as good, or better, than a dry 

 mix, and will need less tamping, but takes longer to set. Never use 

 enough water to wash the cement and sand away from the stone. 



In freezing weather the sand, rock and water should be warmed, 

 but not hot enough to burn and injure the cement. If the concrete 

 is then protected from the frost, there is but little danger of damage 

 from the cold. It is one practice to make a salt solution of the water 

 in cold weather, using one part of salt to every 10 parts of water, 

 to prevent freezing. It is well, however, not to mix concrete in freez- 

 ing weather when possible to avoid it. 



Placing — The concrete should be deposited in place as soon as it 

 is mixed. Cement takes its initial set in a few minutes after water is 

 added to it, and should not be disturbed, else the annealing process is 

 broken and the concrete weakened. It can be injured by too great a 

 drop, 5 or 6 ft., which separates the cement from the aggregate. De- 

 posit the concrete in layers not to exceed 6 or 8 inches and slightly 



