GENERAL METHODS 149 



fit from side to side of the cavity and is nailed to 

 the ledges. In the cavity, back of the zinc, is 

 now packed the hot sand-asphalt mixture. The 

 mixture is made by stirring about six parts of hot 

 sand (rather fine, and preferably of various sizes, 

 down to dust) into the melted asphalt. The mix- 

 ture resembles a heavy bran mash and can be 

 handled with a shovel or trowel. It must be 

 thoroughly tamped. When the filling has been 

 brought up to the level of the first length of zinc 

 another sheet is cut and nailed in place, overlap- 

 ping the first slightly, like shingles. Finally, the 

 metal is tapped over with a hammer to smooth it 

 out and is given a thorough waterproof dressing. 

 This method is of considerable value for filling 

 cavities whose sides are so shaped that the metal 

 can easily be fitted to the sides, and whose sides, 

 either naturally or as a result of bracing, are rigid, 

 the mouth of the cavity not opening and closing 

 slightly in storms, as it is so wont to do. If the 

 latter is the case the metal will be torn from the 

 nails which fix it to the wood. In many instances 

 the metal will be sufficient without the use of an 

 expensive backing of asphalt. In other cases a 

 cheaper backing will be found quite as satisfactory. 

 The value of the metal-front asphalt-sand filling 

 is therefore limited, because it cannot meet severe 

 demands and because moderate demands are as 

 well met by cheaper systems of cavity treatment. 



