CONCRETE CONSTRUCTION 253 



with their inside edges spaced just as far 

 apart as the walk is to be wide. They are 

 then fastened by driving stakes on the out- 

 side and nailing. The concrete is then 

 poured into this form to within about an inch 

 of the top and tamped firmly. A top coat, 

 usually of finer material, is then placed on 

 top of the first layer before it is set, and 

 struck off by running a straight edge along 



Fig. 130. Structure of a concrete walk, a, foundation; 

 b, coarse concrete; c, finish coat of fine concrete 



the tops of the side pieces. This is then 

 troweled by hand to give a smooth and 

 slightly curving surface. 



To allow for expansion and contraction, 

 the walk should be cut into blocks before it 

 sets. This may be done by putting in pieces 

 of thin sheet-iron at regular intervals to be 

 removed when the ' concrete has partially 

 hardened. Sometimes the walk is cut 

 through with a spade while still soft, at regu- 

 lar intervals and fine, dry sand placed be- 

 tween the blocks so made. This is usually 

 quite satisfactory and by careful troweling 



