GENERAL METHODS 147 



of calcium chloride can be used in place of pure 

 water. The mixture will harden three or four 

 times as fast as it otherwise would. This per- 

 centage represents about eight pounds of chloride 

 to ten gallons of water. The chloride costs about 

 twelve cents a pound in small quantities; much 

 less in larger ones. 



Concrete fillings put in during frosty weather 

 must be protected several days with blankets or 

 straw. Some protection, also, is worth while 

 when fillings are put into street trees. Small boys 

 have a mania for scratching on fresh cement in- 

 scriptions which do not enhance its beauty. 



SURFACE-DRESSING ON CONCRETE 



Concrete absorbs water, especially when it is 

 only of moderate density, as concrete fillings are 

 likely to be. To head off this absorption and the 

 decay which usually follows it, every concrete 

 filling should receive a waterproof dressing over 

 its surface. For small fillings which are not much 

 exposed to the weather and dampness, a couple of 

 coats of tar will do very wdl, provided they are 

 applied after the concrete has dried out. In all 

 other cases it is best to give the concrete one or 

 more coats of some special concrete paint. The 

 writer uses Hoyt's cement paint, which has the 

 virtue of sticking to a slightly damp surface. 

 When the paint has dried a coat of tar can be put 



