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Roman cements were natural, highly hydraulic binders, produced from marls – limestones containing clay. This natural combination of calcareous and argillaceous matter required only calcination – below the sintering temperature (800-1200°C) - and the grinding of the burnt stones to produce a binder of remarkable strength and durability. The success of the cement synthesis at low temperatures resulted from the natural intimate mixture of lime and clay (source of silica, alumina and iron oxide) in the marl, which could not be attained in any man-made mixture.

Roman cements can be placed between hydraulic limes and Portland cements. They differ from hydraulic limes in that they do not contain free lime and therefore do not require slaking but rather grinding. They differ from the Portland cements by the different chemistry resulting from considerably lower temperature of calcinations.

They have fast setting times, after the addition of water, with minimal shrinkage. The development of strength in Roman cement mortars is particular: after rapid setting, the increase in strength is relatively slow but, after several months, compressive strength values similar to, or even above, those of Portland cements are recorded.

These features, as well as their warm yellow-to-brown colour, made Roman cements favoured materials for economic and easy manufacture of the stuccoes for the exterior of buildings, highly recommended in contemporary technical literature and textbooks for stuccoists.

The Austrian standard from 1880, modified in 1890, provides a contemporary definition of Roman cements: Roman cements are products obtained from argillaceous marlstones by burning below the sintering temperature. They do not slake in contact with water and must therefore be ground to a floury fineness. It specifies the range of setting times which facilitated the choice of a suitable material for a given decorative task: Roman cements bind fast, medium and slow. By fast binding cements one should understand those which with no addition of sand start to harden within 7 minutes from the moment water is added. Roman cement is considered a slow binding variety if hardening starts later than after 15 minutes’. Other features specified by the standards are: volume consistency under water and in air, fineness of grinding, as well as tensile and compression strengths for various cements and ages, quoted in full below.

Tensile strength [N/mm²]
Compressive Strength [N/mm²]
Roman cement
Portland Cement
Roman cement
Portland cement

< 15 min

> 15 min

< 15 min

> 15 min
> 0.4
> 0.5
> 1
not specified
28 d
> 0.8
> 1
> 1.5
> 6
> 8

Strength specifications for Roman and Portland cement mortars as given by the Austrian standards of 1878 and 1890

The ROCARE Manual with Glossary and Standard: Take a look by activating the field on the left side! (Presently avaialble in English and Hungarian)!
European natural cements - their key technical properties under standardised conditions - (5th Historic Mortars Conference HMC 2019, 19-21 June 2019, Pamplona, Spain)

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IATCS - Institute of Art and Technology / Conservation Sciecences, University of Applied Arts Vienna