84 



forms should be loosened after not less than two 

 weeks, to a sufficient extent to permit the form to drop 

 away from the slab for an inch or two. The false 

 work must be left in this condition for at least twenty- 

 four hours. The slab should be carefully inspected 

 while the wedges are being loosened. At the end of 

 the twenty-four hours the posts and joists can be 

 carefully removed and the form taken down. The 

 side forms of beams and girders should be removed at 

 the same time as the slab forms, but the shoring be- 

 neath them must be left in place. 



Immediately after the removal of the slab forms, the 

 slabs should be shored up. These shores should be 

 left in position for at least one week. If the^ floor slab 

 may be called upon to 'support any load exce'pt its own 

 weight these shores must be left in position as long 

 as the possibility of such loading exists. 



The forms and false work supporting beams or gird- 

 ers must be left in place at least three weeks. In re- 

 . moving these supports the wedges must be loosened 

 very carefully. If the beam is liable to receive any 

 load at this* period the shores should be left in position 

 for at least a week or two more. 



Concrete Water. The water must be fresh and 

 from all earth, dirt and sewage or other 

 impurities liable to injure the character of the concrete 

 or mortar. Acids or alkalies are injurious. 



Proportions. The proportions given in the specifi- 

 cations must be adhered to, and some measuring device 

 must be n*ed which will insure accurate proportioning 

 of the various materials. 



Mixing. Machine mixed concrete is preferred. The 



rite for each batch must be first mixed dry until 



it i^ uniform, then the water must be added while the 



mixing is continued. Some mark must be placed on 



: ver so thnt the number of turns of the rnixer 



can be counted. The time required for each operation 



should also be checked, in order to obtain uniform re- 



