PREPARING THE CONCRETE. 217 



Being mixed up into thin mortar, it will not be difficult to 

 get the milk of quick-lime mixed thoroughly through the 

 mass of mortar. The quick-lime should be slaked under 

 water several days before using. This quick-lime will im- 

 prove the walls and when hard will be water-proof. This 

 will give, if stones are also used, about one part of water- 

 lime to 12 or 14 of sand, gravel and stone, and one of 

 quick-lime to about 15 of other materials. This wall will 

 be cheaper than one built wholly with water-lime. 



But if the silo is sunk in the earth, it is better to use 

 only water-lime to 12 inches above the ground, although 

 we have seen such mixed-lime wall stand well below 

 ground; yet the quick-lime does not assist in standing 

 moisture. If built wholly of water-lime, the instructions 

 for the first layer should be followed in all the other layers* 

 The- boxing planks, after the first layer has become hard, 

 are raised just 12 inches, leaving a lap of 2 inches on the 

 wall below. The mortar is then put in the wall-box and 

 stone bedded in as before, and the tiers are carried up in 

 this way to the top. The standards may be kept from 

 spreading in the middle by having a movable clamp 

 hooked across some feet above the boxing. 



Plates 8 x 10 inches are placed on the top of the silo 

 walls, and when the boxes are leveled for the top layers 

 of the walls, three-quarter-inch bolts, 21 inches long, with 

 screw or nut on the upper end and a square bend on the 

 lower end, are used. Place three of these in each long 

 wall, one in the center of the wall and one near each end, 

 12 inches from the end wall. Let the bolt go 12 inches 

 into the .wall. To hold these bolts while filling around 

 them, bore a hole in a narrow strip of board and tack this 

 board across the top of the box just where the bolt is to be 

 placed, the upper end of the bolt being put through the 

 hole in the board, standing perpendicularly and 8M inches 

 above the box, so as to take the plate. These bolts will 

 10 



