The first step in the preparation of common lime mortar is the slaking of the lime. This should be done by putting the lime into a water-tight box, or at least on a platform which is substantially water-tight, and on which a sort of pond is formed by a ring of sand. The amount of water to be used should be from 2 1/2 to 3 times the volume of the unslaked lime.

The "volume" of unslaked lime is a very uncertain quantity, varying with the amount of settlement caused by mere shaking which it may receive during transit. A barrel of lime means 230 pounds. If the barrel has a volume of 3.75 cubic feet, it would be just filled by 230 pounds of lime when this lime weighed about 61 pounds per cubic foot. This same lime, however, may be so shaken that it will weigh 75 pounds per cubic foot, in which case its volume is reduced to 81 per cent, or 3.05 cubic feet. Combining this with 2 1/2 to 3 times its volume of water, will require about 8 1/2 cubic feet of water to one barrel of lime. On the other hand, if the lime has absorbed moisture from the atmosphere, and has become more or less air-slaked, its volume may become very materially increased.

Although close accuracy is not necessary, the lime paste will be injured if the amount of water is too much or too little. In short, the amount of water should be as near as possible that which is chemically required to hydrate the lime, so that on the one hand it shall be completely hydrated, and on the other hand it shall not be drowned in an excess of water which will injure its action in ultimate hardening. About three volumes of sand should be used. to. one volume of lime paste. Owing to the fact that the paste will, to a considerable extent, nearly fill the voids in the sand, the volume obtained from one barrel of unslaked lime made up into a mortar consisting of one part of lime paste to three parts of sand, will make about 6.75 barrels of mortar, or a little less than one cubic yard.