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Created Date Monday, 20 May 2013
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WHY IS TYPE S HYDRATED LIME SPECIAL? Margaret L. Thomson

Type S hydrated lime is defined by high early plasticity, high water-retention values, limited oxide
content, and minimal coarse fraction. These qualities are highly valued for plaster and mortar. At the
turn of the 19th Century in the United States, lime calcined from dolomitic limestone in Ohio was
recognized as the best lime for interior plaster use. Starting about 1910, The American National
Bureau of Standards, in collaboration with The National Lime Association and other masonry material
producers, started what was to become a 30-year effort to characterize the nature of hydrated lime for
building construction. They developed most of the methods of testing and definitions of key
properties used in today’s specifications. Commercial awareness of the value of producing a
hydrated lime that would achieve all these properties in a reproducible manner led to two patented
technologies that are used today. No other lime industry or standards development organization in
the world has looked at hydrated lime in the same manner. The original characterization effort plays a
continued important role in both the plaster and mortar industries of today.

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