A remarkable example of a natural cement building, the Saint-Merri Church in Paris, France 

Way back when…

Once upon a time, there was a chapel called Saint-Pierre-des-Bois. The abbot of Saint-Martin d’Autun, Merri, accompanied by his disciple Frodulphe, set up shop next to the hermitage. They had come in pilgrimage to the tombs of Saint Denis, Saint Germain and Sainte Geneviève. On August 29, 884, the relics of Saint Merri “translate” the body of the saint, which is outside the walls for its protection. A new church was constructed by Eudes le Fauconnier (whose name still appears on the paving stones in the choir stalls of the current church) and dedicated to Saint Pierre and Saint Merri…

Much later … during the reigns of Louis-Philippe and Napoleon III. A campaign was waged between 1835 and 1856. The construction that interests us here – the façade – is accounted for by the movement in favour of historic monuments and the Concordat signed under Napoleon, as well as the Paris Prefect Rambuteau, during which the city was modernised in preparation for the Haussmann plan. The façade dates from the reconstruction of the primitive church, which became necessary as the population of Paris increased under François I.

The three-door entry on Rue Saint-Martin is rich in decoration, made up of a multiplicity of canopies, pinnacles arched mouldings and sculpted frieze. Only the arcature panels of the large central door date from the 19^th century. The relationship between humans, plants and animals is so remarkable that it seems historic. The restorers were able to mend, restore or invent from their own imaginations. 

Vassy cement, an Avallonais mine supplies Paris

1830: The former notary, Mr Gariel, an amateur geologist, analysed stones where other researchers had expected to find shale. He fired a few samples; once the fire had died out, they fused into powder. An idea came to him. He mixed the product as he would lime. The mortar set very quickly, and the result seemed to him better. Harder, natural cement sets in the air as well as underwater. Kilns and grinders were soon to be constructed. 

The new material was rapidly tested in rendering a brick arch. The natural cement mortar was so strong that the thickness of the masonry could be substantially reduced. The importance of this discovery and its applications are down to the presence of a young civil engineer in Avallon, who led the first application works in the region and subsequently, in Paris, initiated the natural cement revolution across all the major construction projects of the Second Empire.

Natural cement, serving image and time

Back to Saint-Merri church… The restoration programme launched in 1835 included the statues, which had to be repaired, as well as some decorative elements. The interior circular moulding of the central door dates from the 16^th century, and its representation of oak leaves and acorns, vine stocks, twisting vines, bunches of grapes and chimera animals, the circular mouldings of the two side doors, with a musician to the right with his bagpipes, the rampants of the central gable with curly kale and snails, and partly, the cornice of the first floor, with a frieze of fruits and thistle leaves, a man in a hat carrying a bunch of firewood, chimera and finally, the strips that double the frieze between the gables and the pinnacles, with a fallen angel, a few more bunches of grapes and a number of chimeras. 

The advantages of natural cement in Saint-Merri are two-fold: moulding and resurfacing. On November 12^th, 1840 the archaeologist Ferdinand de Guillermy wrote to the public instruction ministry: “Under the pendance of the arch moulding on the door to Saint Merri … we have placed statuettes in moulded imitation stone, in the manner of those which decorate the southern door of Notre-Dame.” The architect was Mr Godde, who in a book signed by Amblain in 1939 introduced an “imp” at the top of the arch moulding of the central part called a “baphomet”. This image, which was that of the idol of the Templars, was the subject of much discussion. In 1856, when the diocese architect was Baltard, Mr Vaugeois, a Paris entrepreneur based at 32, rue Saint-Paul au Marais, was commissioned “to refurbish all the moulding joints on the door … as Gothic ornamentations using Vassy cement”. 

It should be noted that the apostolic cortège in 1842 ordered that the statue assembly under the canopy on both sides of the central port of the door and above the two side doors be made with Saint-Maximin limestone by the sculptors Brun and Desprez. The moulded statuettes of the arch moulding had been placed there at the end of the previous decade. At the time, the southern Saint-Etienne de Notre Dame” door had not yet been restored and reworked by the sculptor Geoffroy-Dechaume and his workmen. Indeed the comparison led to the discovery of six subjects and treatments directly modelled on prints of a monk and a priest holding a closed book, a righteous man holding an open book, a bishop, and the two saints, Laurent and Georges. The twelve other statuettes of this series of 18 are pure invention. They are a beautiful example of recreation. They are either placed on the canopy in original stone or affixed to the wall.

Vassy mortar, “a slightly pinky-yellow ochre with a fine texture” (as reported by Bruno Perdu in 2001) that maintains its hardness, even though rainwater slightly alters its surface, is a “hydraulic binder mortar mixed with limestone sand compatible with Vassy cement” (cf. report). This allowed the jointing to be pointed, and the chips, spalls and edges to be meticulously repaired and therefore re-establish a clear interpretation of relief and a fine ornamental succession, with an trabiation frieze, rampant and intrados of the gable, canopies, brackets and piers supporting statues at the foot of the central door, arch rampant brackets and canopies of statuettes, the brackets and gables of the niches in the side doors, canopies and the brackets of the abutment. 

The original Saint-Leu stone was prepared using a chisel to fix the resurfacing mortar, and strengthened with iron to ensure the bond of key elements. Both the resurfacing mortar and that used for the moulding seemed very similar, and therefore from the same source. “The angel’s head to the top left is today broken, showing that, once moulded, the statuettes were chipped with the tool so as to allow them to be stuck to the ceiling panel” (cf. report). The mortar, and the confidence of the restoration craftsmen, who launched a major movement, are such that any accidents during the installation of certain statues of the apostolic cortège were repaired using natural cement.

Cements …  questions and answers

Under the direction of Jean-François Legrand, chief architect of historic monuments and a member of the Geste d’Or jury, the restoration site can now use this improved understanding of natural cement and the revelation of a product and a technology from the past and the present to observe the quality of material and its use. Analysis has also revealed reworkings postdating the 1925/1928 period, where documents talk about a metallic cement that analyses have not yet completely understood in terms of either physical or chemical composition, or indeed their provenance. Certainly a lot of work remains to be done as part of this exciting exploration. 

Pascal Payen-Appenzeller 
Stratigraphy heritage expert
With the thanks of Jean-François Legrand