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Natural cement is hydraulic cement made from pulverized and heated limestone containing clay, magnesia, and iron.
When heated in a kiln, and ground to a fine powder, a type of cement is produced, that, like portland cement, sets and hardens when mixed with water through chemical reactions. Strength and uniformity of natural cements are lower than for portland cements, but these are much more historically accurate materials for use on many historic restoration projects, which is their primary application. Natural cements were extensively used in 19th and early 20th century construction, and many historic structures were built with these materials. However, with improved technology for producing portland cements, sales of natural cements began to decline in the late 1800s. Natural cements are available for restoring historic structures and must meet ASTM C10, Standard Specification for Natural Cement.
