85 



suits. A wet or slushy mixture must be made. The 

 color of each batch must be carefully noted as it comes 

 from the mixer. Uniformity of color must be insisted 

 upon. The mixer must be in charge of a foreman. 



The operations of placing the materials in the mixer 

 must be carefully checked and it is advisable that one 

 inspector be especially detailed for this work. The 

 laborers placing the materials in the mixer must be 

 selected for their intelligence and ability to understand 

 the directions given them. 



Freezing Weather. Work must be suspended during 

 freezing weather, except by permission of the engineer. 

 When concrete is to be placed during freezing weather 

 salt must be used in the water if deemed necessary, 

 the water, sand and broken stone may also be heated. 



Foundations and heavy walls, where the face ap- 

 pearance is of no consequence, may be run in freez- 

 ing weather; but great care should be exercised in 

 order to prevent the concrete freezing, by heating the 

 materials and protecting the work. Frozen concrete 

 must be torn out and rebuilt. 



FIG. 31. CORRECT AND INCORRECT METHOD OF RETTING 

 COLUMN HOOPS. 



Hot Weather. During hot weather the sand and 

 broken stone become heated by the sun, sometimes to 

 such an extent that they tend to cause the cement to 

 set in the mixer. In hot weather the stone must al- 

 ways be thoroughly wet down before it is used. If 



