BUILDIXG LAWS 359 



sufficient number of times to effect the thorough mixing of 

 the ingredients. 



"All forms and centering for concrete shall be built plumb 

 and in a substantial manner, made tight so that no part of 

 the concrete mixture will leak out through cracks or holes, 

 or joints, and after completion shall be thoroughly cleaned, 

 removing shavings, chips, pieces of wood and other material, 

 and no debris of any kind shall be permitted to remain in the 

 forms. All forms to be properly supported and braced in 

 a manner to safely sustain the dead load that may be imposed 

 upon them during construction. 



"The reinforcing steel shall be accurately located in the 

 forms and secured against displacement. 



"Concrete shall be placed immediately after mixing. 



"Whenever fresh concrete joins concrete that is set, the 

 surface of the old concrete shall be roughened, cleaned, and 

 spread with cement mortar, which mortar shall be mixed in 

 proportions of 1 of cement to 2 of sand. 



"Concrete shall not be mixed or deposited in freezing 

 weather, unless precautions are taken to avoid the use of 

 materials covered with ice or that are in any other way unfit 

 for use, and that further precautions are taken to prevent the 

 concrete from freezing after being put in place. All forms 

 under concrete so placed to remain unt'l all evidences of frost 

 are absent from the concrete and the natural hardening of 

 the concrete has proceeded to the point of safety. 



"Concrete laid during hot weather shall be drenched with 

 water twice daily, Sunday included, during the first week. 

 The broken stone, if hot and dry, must be wet before going 

 to the mixer. 



"The time at which props, or shores, may safely be removed 

 from under floors and roofs will vary with the condition of 

 the weather, but in no case should they be removed in less 

 than 2 wk. ; provided, that column forms shall not be removed 

 in less than 4 da. ; provided further, that the centering from 

 the bottom of slabs and sides of beams and girders may be 

 removed after the concrete has set 1 wk. ; provided, that the 

 floor has obtained sufficient hardness to sustain the dead 

 weight of the said floor and that no load or weight shall be 



