176 STONE PAVEMENT CH. X 



' Upon the subsoil, thus carefully prepared, there 

 ' should be laid a base of concrete from eight to 

 ' fifteen inches thick, depending upon the amount 

 ' and character of the traffic, and somewhat upon 

 ' the quality of the subsoil — a dry gravel or sand 

 ' requiring less depth of concrete than a clay 

 ' soil. 



' The upper surface of this concrete must cor- 

 ' respond in form to the finished grade of the pave- 

 ' ment to be placed upon it. 



' The pavement itself should be of stone blocks 

 ' about three inches wide, nine inches deep, and 

 ' from thirteen to fifteen inches Ion or. The width 

 ' and depth must be as uniform as possible ; the 

 ' lengths may vary. 



' The blocks should be laid upon the concrete, 

 ' over which a light coat of sand, not gravel, should 

 ' be spread merely sufficient to enable the workmen 

 ' to bed the stones evenly. Less than an inch of 

 ' sand should suffice if the stones are reasonably 

 ' even and smooth. The blocks are set with their 

 1 longest dimension across the street, their smallest 

 ' parallel to the axis of the street. 



'After they are set, a small quantity of fine sand 

 ' must be swept over their surface with brooms, so 

 ' as to fill the joints about half full. 



'The joints should then be filled to the top with 

 ' melted asphalt. This must be done, if possible, in 

 ' dry, warm weather, and cannot be done when the 

 ' stones are wet. 



