240 ART OF BUILDING. 



1. Pit sand, mixed with lime, makes a better mortar 

 than river sand. 



2. Pit sand, fresh dug, makes a better mortar than that 

 made of the same sand dried in the sun. 



3. A mixture of lime and old mortar as cement, forms 

 a better mortar than the best sand and lime. 



4. The darkest colored sand makes the best mortar. 

 It would be vain for us to attempt giving any rules as 



to the proper proportions of sand and lime to form a good 

 mortar, owing to the various qualities of the lime ; if it is 

 perfectly pure and caustic, fifty parts of sand to one of lime 

 would be the proper proportions ; but the most common 

 proportions in this country are two parts of sand to one 

 of lime. In this country our masons err greatly in using 

 too little sand, and in not mixing what they do use tho- 

 roughly and intimately with the lime. The quality of the 

 mortar depends essentially upon the slacking of the lime ; 

 it is of the utmost importance that every particle of the 

 lime be thoroughly slacked ; if any parts of it are mixed 

 up before it is slacked, the water continuing to act upon 

 it, will cause it to expand, and in plastering will cause 

 blisters. But a small quantity of lime should be slacked 

 at a time unless it is protected from the air, as it will 

 absorb carbonic acid gas from the air, which injures the 

 mortar. 



Cement Puzzolanas, Tarras. For the construction of 

 masonry in water, a peculiar kind of mortar is necessary 

 common mortar will not harden in water. For lining 

 reservoirs or tanks, common mortar may be used, if they 

 are suffered to dry and harden before the water is let in. 

 For hydraulic works, cement, puzzolanas and tarras are 

 mixed with lime, which forms a mortar that sets immedi- 

 ately in water. There are various kinds of cement. The 

 Roman cement which comes from England, is composed 

 principally of a calcined marl. The Dutch cement is 

 tarras and lime, one of the former to two of the latter. 



Puzzolana is the production of volcanoes, and is com- 

 posed principally of marl, and is found in Italy. Green- 

 stone calcined and powdered, mixed with lime and sand, 

 formed the mortar with which the famous Eddystone 

 lighthouse was constructed by Smeaton. 



Grout and Grubbstone mortar. Grout is nothing more 



