Home

New introduction to the 1997 edition of

Observations on Limes

C W Pasley

The book which was published for Sir Charles Pasley in 1838 was in two parts. In the first part he recorded a long series of his own practical experiments towards the development of an artificial cement for military uses, and in the second part he gave his own summaries of many earlier works on the subject of lime.

His own cements were good by the standard of his day, but were soon to be bettered by the development of what we now understand as Portland cement. They were only prepared by the army for its own use and did not have any significant impact on commercial producers. In this context Pasley's development of 'an artificial water cement' was something of a historical backwater. His descriptions of this are very wordy and of only limited use to those involved with the care of historic buildings today. This work, like so many other lime books of that period, must be seen in the context of the military mind. The issues of strength generally and more specifically the sound construction of hydraulic engineering works were clearly of military significance. The author was able to devote considerable resources to pound away (quite literally with mortars and cannon in one example) at the questions which occurred to him and he spared no ink in describing the results.

On the other hand Pasley's reporting of the work of other authors in the second section of his book is of great interest today. Many of the works he discusses are now very rare and Pasley's text gives us a good insight, from his strongly biased viewpoint, into the interesting developments of the eighteenth and early nineteenth centuries. It is those chapters which have been reproduced here. They show the contrast between those, like Dr Higgins, who set out to achieve exceptional performance from the simplest of limes,and those, like John Smeaton, who understood how strength for the toughest conditions could be achieved from impure limes.

Our earliest text on the use of lime for building is in Vitruvius' Ten Books on Architecture which embodied the conventional wisdom of the eighteen hundred years from its writing in about 25 BC (and very probably from well before that time) until the publication in 1791 of John Smeaton's experiments.These had been carried out in preparation for his building of the Eddystone Lighthouse in 1756. The conventional wisdom had been that hard durable mortars came from lime prepared from the hardest limestones and preferably from moist, shady quarries. In contrast it was believed that soft stones, such as chalk, should only produce soft mortars. Over all of those years craftsmen must have been biting their tongues because the facts simply do not support the theory. Although the moisture in the limestone and the hardness of the stone do have some beneficial effects these are far less significant than another property which had not been explained. In his kitchen sink tests Smeaton showed that the limes which developed a firm set for 'water building' were those made from limestones or chalks which contained a suitable proportion of clay. In 1796, just five years after the publication of Smeaton's work, The Reverend James Parker took out a patent for 'A certain Cement or Terras to be used in Aquatic and other Buildings, and Stucco Work'. This was prepared by calcining Septaria which are concretions of limestone and clay which occur in the clay beds of certain rivers. The proportions of limestone and clay in the septaria are highly propitious so that when they are fired at an appropriate temperature and then ground to a fine powder they produce a very quick setting cement quite unlike anything which had been seen before. The monopoly granted by the patent was well exploited in England for the fourteen years for which it ran and the cement was sold as 'Roman Cement', even though it had no connection with the famously durable mortars of some surviving structures from ancient Roman times.

In France there were parallel activities and 'cement stones' were identified at Boulogne sur Mer in about 1796 (or perhaps 1798) by a military engineer. From 1810 onwards, when Parker's Patent had expired, there were several successful producers of natural cement in England whilst French engineers developed a natural cement industry in St Petersburg. As late as 1823 King Wilhelm I of Wurttemberg sent Friedrich Schmidt to spy on the natural cement industry in England and set up a works in Germany. For engineering works and for prestige building projects natural cement was very widely used right up to about 1850.

But other engineers and manufacturers began experimenting with artificial cements made by blending limestone, or chalk, or even lime, with clay and firing the product. In France in 1818 L. J. Vicat published his series of experiments, begun in 1812, and Maurice St Leger set up an artificial cement works at Meudon near Paris. St Leger also took out an English patent in 1818, though it is unlikely that he exploited it. In England James Frost had taken out Patents for cement in 1822 and 1823, had bought a site in Kent in 1825 and was making two types of cement by 1828 when Pasley first contacted him.

Frost was operating commercially in very much the same field where Pasley was experimenting in the army. From 1826 Pasley was responsible for teaching 'Practical Architecture' to the junior officers of the Royal Engineers at Chatham in Kent. He carried out some unsuccessful experiments to make an artificial cement at that time before the more successful experiments with a colleague, Major Reid, from 1828 onwards. The materials he made could just better the performance of the natural cements and were significantly better than Frost's cement.

It is curious that Pasley had never heard of Joseph Aspdin until they met at the 1851 Exhibition. Aspdin's patent of 1824 'for making artificial stone' is widely, but misleadingly, supposed to have been the beginning of the Portland Cement industry as we now know it. In the patent he used the term Portland Cement to give an impression of excellence and the suggestion of an attractive colour by association with Portland stone. Aspdin's cement at that time was comparable to that of Frost and St Leger. As Christopher Stanley has noticed, this patent was taken out within three months of the expiry of one taken out in 1810 by Edgar Dobbs for 'Compositions for making waterproof cement' which may have inspired it. It was not until about twenty five years after Aspdin's first patent that the real breakthrough came with the sintering of the mix at higher kiln temperatures. It was only this that gave a clear edge in strength of artificial cements over natural cements.

The texts which Pasley summarised or condensed included the most important ones from England and France together with a few notes from military sources in India. From the eighteenth century we are given Belidor (1739 and 1753), de la Faye (1777), Perronet (1788), Colonel Fanshawe (1792), Semple (1776), Smeaton (1791) and Parker (1796). From the early nineteenth century we have Gayton (1800), Fleuret (1807), St Leger (1818), Vicat (1818 and 1828), Dr John (1818), Robert Stevenson (1824), Telford (1828), General Treussart (1829), White (1832), and Godwin (1836). Of these Smeaton, Vicat, Treussart and Godwin are reported in detail. There are also comments on asphaltic or bituminous cements and analyses of various cements and hydraulic limes. He describes the use of Magnesia cements in India in the 1830s and his own researches on such materials in 1828. Because of the white colour of this cement it could easily be overlooked in modern conservation work.

His final paragraphs utterly condemn the use of common chalk lime mortar.

Michael Wingate
Hindolveston. September 1997.

Return to
Observations on Limes