ROSENDALE NATURAL CEMENT CHEMISTRY:
HOW IS IT DIFFERENT FROM OTHER CEMENTS AND BINDERS?

What is Natural Cement?
Natural cement is hydraulic cement made from limestone that has a high clay content (argillaceous limestone). It is different from building lime, which is made from limestone with a lower clay content, in that lime is not hydraulic (does not set under water).

Lime and Natural Cement are both produced by heating limestone to approximately 900 to 1100⁰C, at which point carbon dioxide bound within the stone is released. In the production of lime, the burnt material is quicklime, which is then mixed with water to make building lime, also referred to as hydrated lime or lime putty. The process of hydrating quicklime is slaking, and when quicklime is slaked, it crumbles to a fine particle size. The burnt natural cement rock does not slake when mixed with water, however. Instead, it must be crushed into a powder before use. The resulting powder is natural cement, which will set when mixed with water, and hardens through a process of cement hydration.

When lime is used in masonry mortar and renders, it does not set due to being mixed with water, but rather, must react with carbon dioxide in the air in order to cure and harden. This is a slow process, often requiring weeks or months to build significant initial strength.

Portland cement is made from artificial mixtures of limestone, shale, gypsum and other additives. The mixture is heated to approximately 2300⁰F, at which point components fuse to form a clinker. The clinker is then ground to a fine powder that sets when mixed with water.

Hydraulic lime may be made either from blends of lime and pozzolans (such as slag, clay or ash) or by burning of limestone with naturally occurring silica and/or alumina impurities. It is closely related to natural cement, but contains excess free lime, allowing the material to be slaked to a fine powder after burning. The excess of lime may reduce durability, lengthen set time and diminish initial resistance to weather, however, particularly in severe exposures such as coastal and cold weather environments.

Although artificial mixtures of hydraulic lime and clay have been marketed as Rosendale Cement equivalents, this is chemically not the same as natural cement, nor does it have any connection with the historic Rosendale cement region. These artificial mixtures are fundamentally different from true natural cement by definition. Natural cement is simply the product of burning natural cement rock. American natural cement was never a mixture of ingredients such as clay or other pozzolans and lime or hydraulic lime. The use of such artificial mixtures is historically incorrect, therefore, as it is not the same as replacement-in-kind. Only authentic Rosendale Natural Cement from Edison Coatings, Inc. is an historically accurate replacement in kind for restoration of buildings, structures and monuments constructed from the same material from the same source.

ROSENDALE NATURAL CEMENT vs. OTHER BINDERS

BINDER COMPOSITION REACTIONS CHARACTERISTICS NATURAL CEMENT Dicalcic Silicate and Aluminate; Produced from argillaceous limestone Hydration, Crystallization Upon Water Contact Fast Initial Set, followed by slow, gradual rise to final strength. Lower strength than Portland cement, similar strength to lime, lime putty, hydraulic lime. HYDRATED LIME & LIME PUTTY Calcium Hydroxide; Produced from limestone. Forms Calcite w/Prolonged Carbon Dioxide Exposure Slow set and cure, tends to react incompletely below surface. PORTLAND CEMENT Dicalcic and Tricalcic Silicate, Tricalcium Aluminate; Produced from mixtures of limestone, shale, gypsum, other additives Hydration, Crystallization upon Water Contact Controlled Set Times, Rapid Strength Gain HYDRAULIC LIME Calcium Hydroxide, Dicalcic Silicate and/or Aluminate. Produced from limestone with silica or alumina impurities, or from blends of lime and pozzolans. Forms Calcite w/Prolonged Carbon Dioxide Exposure; Hydration, Crystallization upon Water Contact Generally slower setting than natural and Portland cements, faster than lime/lime putty, slow rise to moderate/low strength

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Rosendale Natural Cement is produced by:

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