Briac Thomas
Civil engineer, Lefèvre (France)
On April 15, 2019, a serious fire struck the Notre-Dame Cathedral. Since then, the most important phases of restoration have been completed, and every day work is being done to restore the monument to its former splendor.

A decisive first phase completed

On 15th April 2019, as the world looked on in shock, a serious fire broke out in Notre-Dame Cathedral in Paris, a jewel in the crown of Gothic architecture. It took almost 15 hours for firemen and teams of specialists to bring the fire under control. Since then, the most important phases of the restoration work have been completed and every day skilled craftsmen and workers are labouring alongside one another to bring the monument back to its former splendour. The restoration work on Notre-Dame Cathedral, which is scheduled for completion in December 2024, is being carried out with the utmost respect for the structure and with the competence of various experts in the restoration of historic monuments

All the roofs destroyed or weakened by the fire have been rebuilt and consolidated. Only the vaulted ceilings in the transept remain to be rebuilt which will happen in the next few months after removing the scaffolding used for rebuilding the dome whose cross has already been installed back on its place.

Mapei is particularly proud to be part of this extraordinary project, collaborating with companies of the calibre of Lefèvre and CCR (BALAS Group) which were awarded the tender commissioned by the Rebâtir Notre-Dame de Paris Public Authority for the restoration of the vaulted ceilings of the transept,the two wings of the transept and the central nave (Lefèvre) and of the choir (CCR).

The product employed for this fundamental phase of the restoration of Notre-Dame was a pre-blended, natural hydraulic lime (NHL) and Eco-Pozzolan mortar, which was reinforced with a glass fibre mesh, a solution specifically developed for consolidating historic structures and approved by the team of three architects specialised in historic monuments who are leading the project: Philippe Villeneuve, Rémi Fromont and Pascal Prunet, with advice on structural strengthening provided by the Italian architect Carlo Blasi.

The solution proposed by Mapei underwent a whole year of testing, with numerous experiments conducted in the lab and on site, before being finally approved by the three architects.

Reconstruction work on the vaulted ceilings started in the spring of 2022 after the teams of builders and stonemasons had been trained by Mapei on how to use the solution correctly.
We interviewed Briac Thomas, the engineer in charge of the works for Lefèvre.

(C) MAPEI France

What is the scope of your work and what are the technical specifications of the products you use?

Lefèvre worked on all the upper sections of the nave and the two wings of the transept, treated with a hydraulic lime and Eco-Pozzolan mortar. This structural work, which acts as a kind of shell,  gives back the masonry vaulted ceilings their original resistance and shape, alleviating the effects of any future movements and preventing fractures in the joints with the adjacent structures. 

An hydraulic lime and sand based mortar was injected in the most severely damaged joints between the stones to ensure perfect sealing, with a with particular attention paid to the most exposed areas.

All these activities are mainly carried out at height where safety measures have to be particularly stringent. The workers wear safety harnesses whenever necessary and, when this is not possible, temporary structures need to be erected to provide protection.
Wooden arches at the cross-point of the transept that enabled the reconstruction of the diagonal arches and the oculus of the oculus of the vaulted ceiling. (c) Romaric Toussaint_Rebatir Notre Dame de Paris

What are the challenges for companies working on a project of this scale, part of our millennia-old historical and cultural heritage?

It is an incredible honour and a privilege to work on the rebirth of Notre-Dame Cathedral, a part of our cultural heritage renowned all around the world that draws in pilgrims and tourists from every corner of the globe. It is an extraordinary project, one where we are able to put all our most advanced knowledge and expertise into practice, and there is no doubt that it can be regarded as just the start of a new horizon in terms of growth.

Reconstructing a building identical to the original is a real challenge, as well as an enormous responsibility! This project is truly out of the ordinary, in which every detail has been meticulously studied in order to guarantee that everything proceeds at the right pace and that the right decisions are made at the right time. Having to reconstruct a building exactly as it was, rather than restore it, is pretty intimidating, it is an incredible commitment, as well as being a real mission!

With such an emblematic project there is so much at stake, so it is fundamental that pre-set deadlines and schedules are respected. And while we are on the subject, being able to rely on the most cutting-edge technology is of enormous help because working on something that is part of our heritage does not necessarily mean it is not of our time! For example, we have one of the largest cranes in Europe available reaching a height of 89 m, and equipment to spray-apply mortars that not only helps save time, but also makes the work of site operatives considerably easier.
Working at height with a safety harness. (C) MAPEI France

A site of this scale is a human endeavour that encompasses a wide range of skills and expertise. What is the relationship like between all the various teams on site?

The mood on site is really good: there is a lot of mutual respect between all the teams and a true sense of collaboration. And everyone is also on first-name terms! There is daily and detailed exchange of information with the architects: we all collaborate to achieve the same objective. The method adopted, whereby the solutions we intend using undergo preliminary testing, makes things a lot simpler and we are able to proceed more quickly!
The team from Lefèvre at work on the extrados of the vaulted ceilings in the upper sections of the central nave and transepts. (c) Lefèvre

Lefèvre Company

Lefèvre was founded in 1944 following the need to reconstruct and restore France’s architectural patrimony. The first projects undertaken by the company were in the Caen region which had been badly hit by the Normandy landings. The company then extended its area of activity towards l'Ile-de-France and the large western area of the country, regions with a particularly rich patrimony. The company concentrates on stone-cutting and masonry work on the one hand, but also on restoration and renovation work. With its long experience, Lefèvre has a team of 450 people available distributed throughout 12 branches located all over France, one of which is the corporate head-office in Gennevilliers, responsible for the Notre-Dame Cathedral site.
Application of a natural hydraulic lime (NHL) and Eco-Pozzolan mortar enabled the vaulted ceilings to be consolidated during both the reconstruction and restoration phases. (c) Mapei France

Project Information

Notre-Dame de Paris, Paris (France)
Period of construction: 1163- mid 14th century
Original design: Jean de Chelles, Pierre de Montreuil, Pierre de Chelles, Jean Ravy and Raymond du Temple and Eugène Viollet-le-Duc
Owner: Rebâtir Notre-Dame de Paris Public Authority
Design of the restoration intervention: Philippe Villeneuve, Rémi Fromont and Pascal Prunet
Consultant for structural strengthening: Carlo Blasi, Studio Comes
Contractors involved in the work: Lefèvre and CCR (Balas Group)
Mapei coordinators: Xavier Blaise-Martin, Mapei SpA (Stefano Ambrosi, Giulio Morandini and Paolo Baldon)
Photos: Xavier Blaise-Martin and Bérangère Lomon.
Briac Thomas
Civil engineer, Lefèvre (France)
Photo/Video Gallery
Product Lines
Products for structural strengthening
You might also be interested in
Torre Velasca
Torre Velasca
Camerino Cathedral rises up from the rubble thanks to FRP structural strengthening systems by Mapei
Camerino Cathedral rises up from the rubble thanks to FRP structural strengthening systems by Mapei
Strengthening and seismic upgrading work for Villa Alba
The expert's opinion
Strengthening and seismic upgrading work for Villa Alba

In the article we mentioned: