WHY IS TYPE S HYDRATED LIME SPECIAL? ∗

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. Key-Word