132 FARM BUILDINGS IN SOUTH AFRICA 



the studs consist of 2" by 3" deal (see Figs. 187 and 182). In the 

 case of 1-inch sheeting, the distance between adjacent studs should 

 not exceed 2 feet. For 1^-inch sheeting the distance between studs 

 may be as much as 4' 6". 



The forms should be practically water-tight, and they should be well 

 braced against the pressure of the concrete and the ramming. 



If a smooth face be desired on the finished concrete -work, the face of 

 the forms must be dressed with a plane ; but when the work is to be 

 plastered there is no necessity for this, since a rough face is desirable 

 in order to hold the plaster. 



White-washing, greasing, or oiling the faces of the forms will prevent 

 the concrete from adhering to them. Metal forms should always be 

 oiled. 



If there be no external pressure on a wall, the forms can be removed 

 whenever the concrete has become too hard to be indented by the thumb. 

 This will usually be in less than 24 hours. If, however, there is earth 

 or water pressure on a wall, the forms should be securely braced against 

 it, and may have to be left in place for 3 or 4 weeks. While the forms 

 are being removed care should be exercised against injuring the concrete 

 work by excessive hammering, etc. 



Depositing. — Concrete is placed between the forms in layers of from 

 6 inches thick for a very dry mixture, to 15 inches thick for a very wet 

 mixture. Each layer should be well rammed or jogged, so as to compact 

 the concrete and expel air. In the case, however, of a very wet mixture, 

 there is danger of too much ramming causing the fine materials, viz. the 

 sand and cement, to work towards the surface and leave the stones at the 

 bottom. A dry mixture may be rammed with a large, flat-faced rammer 

 till the water flushes to the surface (as in the laying of concrete floors), 

 but in the case of a wet mixture most of the working should consist of 

 jogging with a crow-bar or narrow-faced rammer. 



Contraction. — Concrete contracts while setting, giving rise to unsightly 

 cracks. 



The formation of large cracks may be prevented by reinforcing the 

 concrete, say with steel rods or barbed wire running parallel to the 

 length of the wall. The effect of such reinforcement is to distribute 

 the cracking so that, instead of one or two wide cracks being formed, 

 a large number of minute cracks, which do not matter, are produced, 

 distributed over the length of the wall. 



