OCTOBER: FIFTH WEEK 285 



two things are necessary: They must be rigid; any "give," 

 bulge or leak will leave a corresponding defacement on the 

 finished job that cannot be rectified afterward. And the 

 "face" of the form, which comes next to the wet concrete, 

 must be smooth; any crack or roughness will leave a corre- 

 sponding mark on the concrete, or the form may stick to 

 lie concrete so that it will have to be broken away, thereby 

 spoihng the job. The forms are kept from spreading by 

 bracing on the outside and by using bolts and washers at 

 intervals to hold them together. In the latter case these 

 should be well greased before the concrete is poured into 

 the forms, and removed as soon as the concrete takes its 

 initial set — ^when it has become firm, but not hard — so that 

 it holds its own shape. For very smooth surfaces the forms 

 should be carefully fitted and planed and oiled before each 

 using. Bolts, braces, rings, studding for partitions, or 

 anything of that nature, may be put in place and the con- 

 crete made around them, or holes or slots of any desired 

 size and shape may be made by putting in a piece of wood 

 made smooth and well greased so that it may be withdrawn 

 after the concrete is partly set. Holes can be filled with the 

 "finishing mixture." 



Mixing and Tamping Concrete 



Having the forms ready and the materials on hand, the 

 job of mixing, once it is begun, should be done as expedi- 

 tiously as possible. A substantial, smooth, tight platform or 

 a shallow box of suitable size should be provided. On or in 

 this place the gravel, sand and cement, in the order named, 

 measuring each carefully. With a shovel or hoe mix them, 

 dry, quite thoroughly; then add the water a Httle at a time, 

 while continuing the mixing, until you get a uniform, 

 slushy mass just wet enough to pour. The water may be 

 added in quite large doses at first, but as the "batch" ap- 

 proaches the proper degree of slushiness it should be added 

 sparingly. A mixture that is too wet will not make uniform 

 material. 



