248 FARM BUILDINGS IN SOUTH AFRICA 



The walls of the outslope are 9 inches thick, built in English bond, 

 i.e. alternate courses of headers (bricks with their length across the wall) 

 and stretchers (bricks with their length along the wall) laid so as to 

 avoid continuous vertical joints. 



As in the circular part of the tank, those surfaces of the bricks, whether 

 sides or ends, coming into contact with the earth, are dipped in hot 

 tar, and selected clayey material is packed behind the bricks. 



It is advisable to build a few pieces of hoop-iron into some of the 

 horizontal joints at the corners where the walls of the outslope run into 

 those of the tank, as there the bond is liable to be defective. 



Rendering the Inner Surface. — The object of the rendering is to make 

 the tank watertight. The cement plaster consists of one part cement 

 to two parts clean sand. Before applying the plaster, the lime mortar 

 in the joints between the bricks is raked out to a depth of f inch 

 in order to form a key for the plaster. 



Each part of the surface of the brickwork should be well wetted 

 before applying the plaster. This prevents the moisture from being 

 dried out of the plaster too rapidly, and removes any dust which might 

 prevent proper adherence of the plaster to the brickwork. The cement 

 mortar should then be applied, being pressed hard into the brickwork. 



The Inslide. — The inslide consists of a layer of 1 to 2 to 3 concrete 

 2^ inches thick ; on top of this a layer \ inch thick, consisting of one 

 part cement to two parts granite chips, is laid ; this in turn is topped 

 by a layer about \ inch thick, consisting of one part cement to one 

 and a half parts clean sand, finished as smoothly as possible with a 

 steel floating trowel, a little dry cement having first been sprinkled in 

 a thin layer over the surface. Some hours afterwards, the final smooth 

 finish should be given by rubbing the surface over with the steel floating 

 trowel. 



The angle of the inslide with the horizontal shown in the accom- 

 panying drawings is a little over 30 degrees (see Fig. 197), which is 

 slightly steeper than in the experimental tank. In the latter the inslide 

 worked very well, but it was thought that it might be just a little steeper. 



In the tank, as originally built, the inslide was 3 feet 6 inches long. 

 This length was found to be too short, and was increased to 5 feet with 

 satisfactory results. This is one reason why the tank is shown in the 

 drawings as 6 feet in maximum diameter, in place of the 5 feet of the 

 experimental tank. 



