132 CEMENT AND CONCRETE 



128. Cast, Wrought or Galvanized Iron Forms. These 

 are used where a smooth surface is desired without further 

 treatment after removal of forms. In construction work, 

 where the same type of form is used a great number of 

 times, it is economy to have a material which will not go to 

 pieces, warp, swell and crack, even tho the first cost may be 



FIG. 143. Commercial post mold. 



higher. Steel forms, if strongly built, will meet these condi- 

 tions. Forms made of iron are more easily cleaned, and can 

 be used a great number of times. Rusty iron is not good for 

 forms; the concrete will stick badly. There are steel forms 

 on the market for concrete posts (Fig. 143), water tanks, silos, 

 etc. 



129. Wood Forms. Wood forms are most common, and 

 are used most for concrete work on the farm. The chief rea- 

 son for this is that lumber can be obtained easily in small 

 quantities, and there is always a certain amount of old lumber 

 around every farm. 



130. Requirements of a Good Form. 



a) One that can be used a number of times. 



6) One that is strong so it will not bulge or crack. 



c) One that is tight and free from leaks. 



