Roman cement

For the architectural material actually used by the ancient Romans, see Roman concrete.

"Roman cement" is a substance developed by James Parker in the 1780s, and finally patented in 1796. It was, in fact, nothing like any material used by the Romans, but was a "Natural cement" made by burning septaria - nodules that are found in certain clay deposits, and that contain both clay minerals and calcium carbonate. The burnt nodules were ground to a fine powder. This product, made into a mortar with sand, set in 5–15 minutes. The success of "Roman Cement" led other manufacturers to develop rival products by burning artificial mixtures of clay and chalk.

There has been recent resurgence of interest in Natural Cements/ Roman Cements due mainly to the need for repair of facades done in this material in the 19th Century. The major confusion involved for many people in this subject is the terminology used. Roman Cement - was originally the name given, by Parker, to the cement he patented which is a Natural Cement (i.e. it is a marl(or limestone containing integral clay) dug out of the ground, burnt and ground to a fine powder).

Later, in the 1900s various sources of the correct type of marl - known also as Cement Stone, were discovered across Europe and so there were a range of natural cements (with varying properties) in use across Europe It was in 1824 that Joseph Aspdin 'invented' Portland Cement. This was done by adding various materials together to make an artificial version of natural cement. There then followed a number of independently discovered or copied version of this 'Portland Cement' [Also referred to as Proto Portland cement]. Proto Portland Cement does have a different chemical make up from other Natural Cements being produced at the same time: It was burnt at a higher temperature than other N.C.'s and thus crosses the barrier between traditional Vertical Kiln fired N.C. and the later Horizontal Kiln fired Artificial Cements. This Cement is NOT, however, the same as the modern Ordinary Portland Cement, which can be defined as Artificial Cement.

Artificial Cement: It is with the development in the 1860s of rotating Horizontal Kiln technology that the properties of cement changed quite dramatically and could be argued to result in modern Cement. Certainly it is now difficult to actually define wether an old render was a Natural Cement (Single Source Marl) or an artificial one, but there is no doubt if the cement was Vertically kiln fired or Horizontally. The names Natural Cement or Roman Cement then defines a cement coming from a single source rock. Early or Proto Portland Cement could be used for early cement that comes from a number of sourced and mixed materials. There is no widely used terminology for these 19th Century Cements There had been, due to the need to rediscover this technology, two projects carried out by the European Union ROCEM and subsequently ROCARE (an ongoing project). Both these only deal with Natural Cement - referred to as Roman Cement without reference to the early artificial cements.