222 FARM BUILDINGS IN SOUTH AFRICA 



can be drawn together, or pushed apart, as required by simply adjusting 

 the positions of the nuts upon these screws. The moulds should be 

 strong and rigid, and, at the same time, as light as possible. Figs. 171 

 and 172 give the dimensions, while Fig. 173 is a perspective view of one 

 section of the inner mould which gives a clear idea of its construction. 

 It will be noticed that the forms are faced with galvanised iron. This 

 iron projects 10 inches beyond the woodwork of each sectional form, so 

 as to bridge the space between the ends of the forms when these are in 

 position. The galvanised iron should be greased, or oiled, just before the 

 forms are set in position preparatory to being filled. This prevents the 

 concrete from adhering to the iron. 



The forms should be made by a skilled carpenter, as the whole work 

 largely depends on them ; in fact the erection of such a silo should be 

 entrusted only to skilled men, it being desirable to employ a man 

 experienced in reinforced concrete work for the concreting. 



It is essential that the forms should be constructed with their 

 cylindrical surfaces exactly at right-angles to their top face. This 

 condition is necessary for the easy construction of a truly vertical 

 wall. 



Erection. — It is unnecessary to give a full description of the erection 

 of the silo, as the work is similar in many respects to that involved in 

 the erection of the reinforced concrete cattle-dipping tank dealt with in 

 Chapter XXII, a few special points, however, require mention. 



Excavation for Foundation. — As shown in the drawings, the surface 

 of the silo floor is 5 feet below ground level. The hole excavated should 

 be of sufficient diameter to allow of the forms, for moulding the walls, 

 being used right from the bottom upwards. The earth should not be 

 filled in behind the silo wall till some weeks after the part below ground 

 has been finished, as ramming in earth behind a " green " concrete wall 

 might injure it. 



If the ground at the bottom of the excavation be at all soft, it should 

 be well rammed before depositing the hard-core. The hard-core also 

 should be well rammed. 



Should trouble be encountered, due to water oozing into the excava- 

 tion, a temporary sump may be dug at the centre, from which accumu- 

 lated water may be baled at intervals. When the floor, with the 

 exception of the part immediately over the sump, is finished, and the 

 walls are high enough to exclude seepage water, the sump may be baled 



