NATURAL CEMENT
PictureCustom-Matched Rosendale 12M Natural Cement mortar was used in the repointing of the American Museum of Natural History in New York City.
NATURAL CEMENT was both technically and historically the material of transition between older lime technologies and modern cements. Like Natural Hydraulic Lime, it is produced from limestone with clay impurities, burned at relatively low temperatures. Unlike hydraulic limes, however, the amount of clay is sufficient to produce a true hydraulic cement, requiring no slaking and no exposure to carbon dioxide in the air during cure, making it capable of setting underwater.
CHARACTERISTICS
Natural Cements are relatively fast-setting, compared with modern Portland cements, but their strength develops more slowly. Typical set times range from just 2-3 minutes for European Natural (Roman) Cements, to 10-30 minutes for Quick-Setting Natural Cements, to 30-60 minutes for regular Natural Cement (the latter is usually achieved by incorporating set regulating additions).

Nominal full cure is achieved at 90 days, rather than 28 (based on standard lab cure at 23 C / 73 F).

Unlike modern cements, which densify and embrittle with age, Natural Cements remain relatively flexible and permeable indefinitely.
Their relative flexibility also allows them to be used at high concentrations and without the addition of lime, if so desired.
AMERICAN & EUROPEAN NATURAL CEMENTS
Because the
geologies of the American and European continents are different from each other, the natural cements produced are somewhat different as well.

European Natural Cements, also often called "Roman Cements" are typically faster setting, and they  develop their strength much more quickly than typical American cements. This property has made them invaluable for use in precasting applications.

American Natural Cements were not widely used for precasting, though there are some noteworthy exceptions, but were ideally suited to masonry construction mortars and plasters.
HISTORY OF USE
Natural Cements were the predominant hydraulic binders in both Europe and North America during the 19th Century. Thousands of Bridges, Aqueducts, Canal Structures, Buildings, Houses, Water Systems, Sewer Systems, Piers, Fortifications, Retaining Walls, Towers, Monuments and other structures built using these materials remain in service today.

First patented in England in 1796 and sold under the name "Parker's Roman Cement", natural cement is unrelated to the cement actually used by the Romans, which was a mixture of lime and volcanic ash. 
Nonetheless, the term Roman Cement is commonly used in conjunction with European Natural Cements.

American Natural Cement was first produced in 1819, and by the 1890's it was in production in at least 70 locations in 17 states. At least 2 sites in Canada were active as well.
Natural cement sales were overtaken in 1900 by Portland Cement, both in Europe and North America.
AVAILABLE PRODUCTS
Rosendale 10C Natural Cement is American Natural Cement produced from rock mined at locations that actively produced natural cement in the 19th Century. It conforms to the requirements of ASTM C10. Regular and Quick-Setting types are available.

MARFIL is a rapid hardening and curing European Natural Cement, produced at the same location in Spain since the 1890's, and containing no additives.

TRANSLANTIC C10 is a quick-setting cement produced from American and globally sourced Natural Cements; It also meets the requirements of ASTM C10.


Ready-To-Use Natural Cement Mortars are also available:
Rosendale 12M Natural Cement Mortars are produced on a custom basis, and incorporate Rosendale 10C Natural Cement.