Mance: Quarry Industrij of Southern Indiana 



153 



3, The mass cools and moisture is fixed by the silicates, although some 

 of the free lime remains unslaked. 



4. The unslaked lime removes this water from the silicates and becomes 

 completely hydrated. 



The time taken for a lime to set depends on a number of 

 factors. Among them is the amount of impurities present, 

 the amount of water used, the air temperature, and the thickness 

 of the lime layer. Fat or hot limes set much more rapidly than 

 lean ones, and when a mason has been taught to use one it is 

 difl&cult for him to handle the other. After the set has started, 

 any movement of the plaster tends to weaken the bond and injure 

 the work. After the first set the lime hydrate takes up carbon 

 dioxide from the air and forms carbonate of lime, as shown earlier 

 in this study. This process is a slow one and in the case of some 

 limes it may be years before the lime has finally returned to the 

 state of a carbonate. The rapidity with which this change 

 takes place depends on the amount of exposed surface of the 

 mortar, the thickness of the layer, and the porosity of the mortar. 

 As this action goes on, a crust of the carbonate forms over the 

 surface of an}^ considerable mass of mortar and protects the 

 soluble hydrate within from being dissolved or changed, and 

 therefore this final condition of a carbonate may never be reached. 



In regard to the final reaction of the lime with the sand 

 in a mortar, S. W. Beyer says in his paper on the ''Physical Tests 

 of Iowa Limes" in Vol. xvii of the Iowa Geological Survey (p. 104) : 



Long contact of lime hydrate mth tinely di^dded silica is known to cause a 

 reaction by which the silica combines with the lime forming a stable sihcate of 

 lime. The extent to which this reaction progresses depends on the physical 

 and chemical qualities of the' siliceous impurities in the lime or of the sand 

 used with it. If these are very fine, chemical action is favored. Silicates, 

 such as clay or feldspar, for example, are more susceptible to attack by the 

 lime than is quartz sand. Hydraulic limes are apt, therefore, other things 

 being equal, to give a more durable final product than the purer limes. In 

 the same way, muddy or clayey sand used with lime, although less desirable 

 at the start, wiU likely contribute to the dm-ability of the mixture in time, 

 because of the development of these stable compounds by the caustic action 

 of the lime. In the case of sihcates, it is probable that other elements, 

 especially alumina, also enter into combination. 



Lime has many uses in the various industries, but by far its 

 most important use is in the production of lime mortars for 

 structural work, interior walls, and plastering. In these uses 

 the lime cannot be used alone on account of the great shrinkage 

 of the lime paste in setting, and its own lack of inherent strength 



