154 CEMENT AND CONCRETE 



sub-base should be provided, and if it is a large one, 

 the central portion may be tamped full of clay to serve 

 as a filler; in this case, not less than 6" of concrete 

 should surround the filler. 

 Working Instructions: 



1) Follow general instructions given for concrete con- 

 struction. Carefully prepare the form for the step to 

 secure correct dimensions as planned the proper area 

 of platform, the correct width of tread and the correct 

 height of riser. It is suggested that the riser be 8" 

 high and the tread 10" wide; then stock 8" boards can 

 be used as the part of form for riser. Have each part 

 of form properly braced so there is no danger of its 

 bulging. 



2) For a solid step, a 1 : 2-1/2 : 5 mixture is adequate. If 

 the step is to be made from one level to another with- 

 out backing, and is to be reinforced, a 1 : 2 : 4 mixture 

 should be used; in fact, for small jobs, such a mixture 

 is best. 



3) Carefully mix the concrete to a quaky consistency as 

 outlined in Sec. 141. Place the material in the form 

 and tamp it lightly, working the coarse aggregate back 

 from the surface to secure a smooth finish. 



4) The finishing coat of one part cement to two parts sand 

 for the platform and the treads should be placed im- 

 mediately after the surfaces have been leveled off. 

 Where it is not desired to give an extremely smooth 

 finish, enough fine material can be worked to the sur- 

 face by troweling, and this can be leveled off. The 

 risers and sides of the steps can be finished only after 



