Good Mortar 139 



ever, are made of stones laid in mortar com- 

 posed of lime or cement, or a mixture of the 

 two, and sand. A large proportion of all the 

 sand nsed for foundation work is markedly 

 inferior, and the mortar is usually very imper- 

 fectly mixed. If water lime is used with the 

 sand it is frequently old, and if old, inferior. 

 Even the cements deteriorate somewhat with 

 age, and the common stone lime is often used 

 after it is partially or entirely air- slaked. If 

 the binding material be inferior and the sand 

 have quantities of fine earth or vegetable matter 

 mixed with it, it will be seen how impossible it 

 is to secure a strong and binding mortar. Even 

 if fresh lime and sharp sand are used, in accord- 

 ance with the usual specifications in building 

 contracts, the mortar bond may still be weak by 

 reason of careless or imperfect mixing. All 

 mortar, even that used for laying stones and 

 bricks, should be mixed until a lime film sur- 

 rounds every particle of sand. Plastering the 

 outside of the wall below the grade line and 

 pointing the wall above cannot make a firm, 

 good wall out of one which has been care- 

 lessly laid or one bedded in inferior mortar. 



Chimneys may provide for one or more flues. 

 Better draft is likely to be secured when sepa- 

 rate flues are provided for each stove or heater 

 than when one flue serves for two or more 



