LINTELS 



45 



arch should, of course, be built in cement mortar. Turning bars are 

 often used for arches above doors and windows in farm buildings. 



If centering be used it should be left in position for at least one 

 week after the arch, which it supports, has been finished. 



Lintels. — While these are sometimes of stone, reinforced concrete 

 is rapidly displacing that material. Reinforced concrete lintels are often 

 used in preference to brick arches. They should be 18 inches longer 

 than the width of the opening which they span, thus having a bearing, 

 at each end, of 9 inches on the brickwork of the jambs. 



Concrete lintels are moulded in position, the mould being formed 

 of boards. A suitable concrete consists of 1 part cement, to 1 part clean 



Fig. 40. 



sand, to 3 parts broken stone. As in all reinforced concrete work, the 

 stone should be broken small, say to pass a |-inch ring, so that it will 

 pack closely around the reinforcement. 



Fig. 40 shows a lintel reinforced with two fencing standards. These, 

 as will be seen from the illustration, are placed near the lower face of 

 the lintel, where they are most effective. 



The following specifications are laid down by the Public Works 

 Department of the Union of South Africa : — 



" Over openings with straight heads cast cement concrete lintels the 

 full thickness of walls, 18 inches longer than the width of the 

 openings, and of the following depths : — 



