200 SAND AND CEMENT 



Lime Mortars. -In lime mortar, besides effecting an econ- 

 omy, the presence of sand is necessary to prevent the shrink- 

 age that would otherwise occur during the hardening of the 

 paste. 



When a mortar is made of lime and sand, enough lime 

 should be present to just cover completely each grain of 

 sand. An excess of lime over this quantity will cause the 

 mortar to shrink excessively on drying, while a deficiency 

 of lime will produce a weak and crumbly mortar. The cor- 

 rect quantity of lime depends on the character of the ingre- 

 dients, the method of treatment, and, to some extent on 

 the judgment of the builder. The mixtures employed vary 

 from l-2i to 1-5. Building laws in many municipalities 

 require the use of a 1-3 mixture, and for most materials this 

 proportion will be found satisfactory, although for rich, fat 

 limes a l-3i or a 1-4 mixture is sometimes preferable. 



In mixing lime mortar, a bed of sand is made in a mortar 

 box, and the lime distributed as evenly as possible over it, 

 first measuring both the lime and the sand in order that 

 the proportions specified may be obtained. The lime is 

 then slaked by pouring on water, after which it should be 

 covered with a layer of sand, or, preferably, a tarpaulin, 

 to retain the vapor given off while the lime is undergoing 

 the chemical reaction of slaking. Additional sand is then 

 used, if necessary, until the mortar attains the proper pro- 

 portions. 



Care should be taken to add just the proper quantity of 

 water to slake the lime completely to a paste. If too much 

 water is used, the mortar will never attain its proper strength, 

 while if too little is used at first, and more is added during 

 the process of slaking, the lime will have a tendency to chill, 

 thereby injuring its setting and hardening properties. 

 Rather than make up small batches, it is considered better 

 practice to make lime mortar in large quantities and to keep 

 it standing in bulk so that it can be used as needed. 



Lime mortar is employed chiefly for brickwork of the 

 second class and its use is continually decreasing as that of 

 cement increases. It is absolutely unsuitable for any 

 important construction, because it possesses neither strength 



