Meulière houses in Versailles: rocaillage, a craft worth preserving

Antoine de Gironde

Oct 25

5 min read

Meulière (millstone grit) is the stone of the villas and small houses built in the Île-de-France region between 1880 and 1930. At once hard and porous, it is not worked like cut stone. Its most characteristic finish, the rocaillage, has become one of the rarest crafts in the region’s heritage.

What is meulière?

Meulière is a rock formed by the silicification of lacustrine limestone in the Paris Basin. According to the geologist Patrick de Wever, quoted by the Fédération Patrimoine-Environnement, it is extremely strong, unaffected by rainwater, impermeable and porous. That porosity defines the material: a pitted, irregular stone that also offers some thermal and acoustic inertia.

Its name comes from the millstones it was once used to make. From 1880 it became the material of bourgeois villas, then of the small houses built after the housing laws of the 1920s. Quarrying stopped around 1970.

A stone long hidden before it was shown

Before becoming the emblem of the late nineteenth century, meulière was already widely used in building in the Paris region, but hidden. Its resistance to water made it valuable for building foundations, cellars and plinths in damp ground, and it was also used as filling material inside walls.

It was not left visible: the regular façades of the classical period concealed this masonry under plaster or lime renders. It was not until the 1880s, with the picturesque movement and architects attentive to materials, that meulière came out of the shadows, was displayed as facing and found in the rocaillage its characteristic decoration.

Rocaillage: a facing that is laid by hand

Rocaillage fills the joints of a meulière wall with a mortar in which small fragments of stone, flint, clinker, ceramic or shell are set. The binder is lime: it lets the façade breathe and can be tinted with mineral pigments to bring out the stone.

It is a work of the hand. The craftsman selects the fragments and places them as the joint is dressed, to achieve an even result. The technique has now almost disappeared.

Italian quarrymen and masons

The history of meulière in the Paris region is also a history of immigration. The quarrymen, mostly Italians from Piedmont, extracted the stone with picks, shovels and crowbars, in a dangerous trade. The most important quarries for building stone were at Grigny and Viry-Châtillon.

In the communes along the Marne, according to the Île-de-France Region’s heritage inventory, Italian masons came from the mountains of Emilia, Piedmont and the Veneto, especially the Val Nure. They arrived in large numbers from 1870. These versatile masons built meulière houses and also made stucco and mosaics.

The art of rocaille, which is older, also spread in the early twentieth century thanks to Italian mason-cement workers, notably in Normandy. In the Île-de-France, these craftsmen took part in building and decorating meulière houses, but the invention of meulière rocaillage cannot be formally attributed to a single trade community.

Léon Bachelin, architect of meulière in Versailles and Le Chesnay

Léon Bachelin (1867-1929) designed many villas in Versailles, Le Chesnay and Viroflay. His buildings combine rocaillage meulière with brick, ceramic set into the façade and wrought iron, a vocabulary typical of the bourgeois house of the Paris region at the time.

A rocaillage project: rue Mansart

On rue Mansart in Versailles, the Atelier d’Architecture Antoine de Gironde had the damaged rocaillage removed from the plinth of a bourgeois villa. Meulière rubble stones, new or reclaimed and compatible, were brought to the site and wedged into the gaps, then the rocaillage was relaid with a custom-formulated lime mortar. About 40 m² of plinth were repaired. Three things matter: the colour of the mortar, its grain size and the hand that sets the stone. For the rocaillage to be harmonious, the gesture must stay consistent from one bay to the next, from the start to the end of the project. The work is finished: it received the Ville de Versailles façade-renovation grant, awarded to façades of heritage interest. Eligibility rests on the quality of the file submitted and on the follow-up of the works: that is the architect’s job, before and during the works.

The plinth tells the story of the house’s material. Above it, the façade is in stucco, a render that imitates cut stone. Behind it, the masonry is mainly meulière. The rocaillage lets you see that construction at the base.

Common problems

On old rocaillage meulière, the fragments eventually fall out when the lime mortar breaks down under weather, pollution and frost. Rising damp speeds up the process at the foot of the wall. Cement repairs make the problem worse: rigid and impermeable, cement traps water in the wall, encourages the stone to burst in frost and is immediately noticeable, because modern mortar is too uniform and too grey.

The two most common mistakes

The first is not to have the work supervised, or to leave the instructions to someone with no experience of rocaillage: without an experienced project architect to give the right instructions, the result is left to chance.

The second is to entrust the work to a contractor who does not master this craft. Rocaillage is recognised by its gesture: an inexperienced hand produces an uneven facing that shows from the street.

The architect’s role

When rocaillage is damaged, the architect acting as project manager steps in at every key stage.

The initial diagnosis. The architect decides what is kept, what is consolidated and what must be cut out and redone.

The specification in the CCTP. The architect defines the appropriate mortar (natural lime, grain size of the sands) and the nature of the fragments to be used.

Control by sample. The architect has samples made and approves them from close up and from a distance: colour of the dry mortar, texture, size and choice of fragments, the quality of the craftsman’s gesture, before the façade is started.

The grant application. The architect prepares the application to the Ville de Versailles and follows it through to the end of the works: the quality of the file determines the grant.

Preserving rocaillage means preserving a material, a technique and a craft memory.

Frequently asked questions

Can rocaillage be redone with cement?

No. The joint must be made with lime, which lets the façade breathe. A cement mortar traps moisture and damages the meulière.

Is rocaillage decorative or structural?

Its main role is aesthetic, but it also helps to fill and consolidate the joints of an irregular stone.