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The burning and slaking of lime and its use in mortars dates back to the far remote past. The exact time when man first recognized the possibilities of using slaked lime mixed with sand to fill cracks in his shelter and bind the rocks, stones, and crude brick together is uncertain. We definitely know that some 4000 yr. ago—possibly much earlier—lime mortar was used extensively as shown in the construction of the Egyptian pyramids so effectively resisting the ravages of time and weather even at the present time. Certainly the use of lime mortar is an old art. In spite of the centuries during which limestone has been burned and slaked to meet the ever-growing demands of mankind, many fundamental factors controlling the properties of the lime putty still remain to be clarified, doubtless because of the large variety of types of limestone. The physical and chemical properties in many instances differ greatly from those of pure calcium and magnesium carbonates encountered in the laboratory. The range in types includes all varieties from the light porous oölitic stones, chalks, and marls to the dense, compact dolomites and crystalline marbles. The compositions also vary widely—from “cement rock,” carrying a large proportion of impurities, such as clay, shale, silicate, and iron minerals, and variable amounts of magnesium carbonate, through a wide range of magnesian limestones to the true dolomitic types and finally to high-calcium stones, some of which carry 1 per cent or less of impurities and a total calcium carbonate content of over 99 per cent. It is therefore logical that the physical and chemical properties of the parent limestone would have a marked effect on the properties of the finished lime products.
Conley, John E.
Associate Chemical Engineer, U.S. Bureau of Mines, College Park, Md.