PROJECTS IN CONCRETE CONSTRUCTION 



145 



plowed; with such a mixture the molds may be re- 

 moved immediately. Good results cannot be obtained 

 if the materials are either too wet or too dry. The 



FIG. 147-a. Making flower box. 



product will stand up due to the adhesiveness of the 

 concrete, and it must be allowed to set thoroly before 

 handling. Careful measurement of materials is an 

 essential requirement of all concrete work. 

 Working Instructions: 



1) Use a 1 : 3 mixture; that is, one part of cement and 

 three parts of sand, for the various jobs outlined. 

 Where coarse aggregate is available, the block may be 

 made of a 1 : 2 : 4 mixture with a 1 : 2 face. 



2) After measuring the sand, spread it out in a thin layer 

 on a water-tight platform; then spread the cement on 

 top of the sand and mix together dry, continuing the 

 turning until the color is uniform and without streaks. 

 Water is then added slowly from a sprinkling can or by 



