SILOS OF REINFORCED CONCRETE 225 



patched place should be wetted every day by the application of water 

 with a whitewash brush, to prevent its drying out more quickly than 

 the surrounding concrete. 



Painting. — The silo should be finished, both inside and outside, by 

 the application of a coat of cement grout consisting of 1 part cement 

 to 1 part fine sand, applied with a whitewash brush. Before applying 

 the grout the wall should be thoroughly brushed over with a dry, stiff 

 brush. Each part of the wall should be well wetted immediately before 

 the grout is applied to that part. It is a good plan to begin painting at 

 the top of the wall and work downwards ; water running down the wall 

 then wets and soaks into that part which has still to be painted. While 

 the silo is being painted the grout of cement, sand, and water should 

 be kept constantly stirred. 



Spraying. — The concrete of the silo should not be allowed to become 

 dry, for at least a fortnight after it has been deposited. It may be kept 

 damp by spraying twice a day with water. 



The silo should not be filled until at least two months have elapsed 

 after the deposition of the last concrete. 



The Roof.— The roof (see Figs. 176, 176a, 177, and 178) is octagonal 

 in plan, and the roof covering is of corrugated iron. 



During the filling of the form in its highest and last position, sixteen 

 ^-inch by 15 inch bolts are set 11 inches down into the concrete, so that 

 their ends project 4 inches above the top of the wall. The wall-plate, 

 which consists of 6" by 3" scantlings, is held in place by these bolts. 

 This plate is cut, fitted, and laid out, to two circles, corresponding 

 to the internal and external diameters of the silo at the top, drawn 

 on the ground. In this way as little as possible of the work is left to be 

 carried out on the top of the silo. 



The main principal, marked A A in the plan, is detailed by Fig. 177, 

 the letters on the different members corresponding to those in the 

 elevation, Fig. 176. This principal is assembled, and put together, on 

 the ground. It will be noticed from the drawings that the tie-beam 

 is double, consisting of two 9" by 1£" scantlings nailed one on each side 

 of the rafters. 



The second principal appears in plan at B B , at right angles to the 

 main principal. It is in halves, one of which is detailed by Fig. 178, 

 the letters in which figure correspond to those in the elevation, Fig. 176. 

 The tie-beam B 2 is attached to the double tie-beam A 8 , of the main 



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