Field notebook extract published in the BRGM journal, Géosciences No. 29: "Talking about Earth".
15 April 2019
The fire started on the afternoon of 15 April 2019, inside the cathedral's wooden roof structure. In just a few hours, the flames destroyed the spire and the entire roof with its supporting beams. The rapid intervention of hundreds of fire-fighters saved the main structure of the building, including the towers and the western façade, as well as numerous works of art and relics. The fire lasted almost 15 hours.
16 April 2019
From the following day, 16 April 2019, a national fund-raising campaign, supervised directly by the President of France, was launched for the conservation and restoration of Notre-Dame de Paris. The funds raised would be used exclusively to finance conservation and restoration work on the cathedral and its furnishings, as well as the initial and ongoing training of professionals with the specific skills required for the work. They were assigned the task of preserving the historical, artistic and architectural worth of the monument.
1 December 2019
A public administrative entity, called Rebâtir Notre-Dame de Paris, was founded on 1 December 2019. Its mission was to conduct and coordinate studies and operations to conserve and restore the cathedral. The fire caused extensive damage to the original stones - Lutetian limestone - generating an extraordinary need for replacement stones: around 1,000 m3 of "dressed" blocks, a volume which far exceeded that needed for ordinary monument maintenance and restoration projects (a few cubic metres to a few dozen cubic metres).
The difficulties encountered on the Notre-Dame site were due in particular to the supply of "new" stone: a sufficient quantity of suitable replacement stone had to be found and made available within a short time-frame, dictated by the site's tight schedule. These had to have physical, mechanical and aesthetic characteristics that were as close as possible to those of the original stones, so as to guarantee technical and visual compatibility (to avoid a "patchwork" effect) between the old and new blocks in damaged areas.
June 2020
The public entity Rebâtir Notre-Dame de Paris asked BRGM for help. Its mission was to supply the restoration site with suitable replacement stone on time. In practical terms, this involved assessing the capacity of the Lutetian limestone quarries that were still active to supply stone that was compatible with the cathedral’s original stone and to meet all or part of the need for "new" stones.
July 2020 - June 2021
Each of the 9 Lutetian limestone quarries was investigated by BRGM geologists to determine its "geological cross-section". This led the scientists to inventory and sample 32 types ("qualities") of stone of potential interest for the restoration of Notre-Dame.
Each quarry sample was subjected to various laboratory analyses to obtain a complete physico-mechanical characterisation: porosity, compressive strength, etc.
Observations with the naked eye and a microscope provide a precise description of each quarry sample: its colour, texture, grain size, "shell" character (whether or not it contained fossils), etc. Each sample was then compared with samples of stone from the cathedral from an aesthetic point of view.
June 2021
Based on the results of this study, BRGM drew up a methodological guidebook for selecting stones for the restoration of Notre-Dame de Paris. It also included a collection of reference samples, intended primarily for the architects in charge of the restoration work. They used it extensively, moving around the cathedral and using the samples to visually select the stone closest in appearance to the old stones for each damaged part.
Stone supply during the reconstruction of Notre-Dame de Paris
The Croix-Huyart quarry.
© BRGM - J. Bodin
BRGM testing and checking raw blocks in the Croix-Huyart quarry.
© BRGM - D. Dessandier
BRGM testing and checking raw blocks in the Croix-Huyart quarry.
© BRGM - D. Dessandier
BRGM checks the quality and traceability of pieces cut in stone-cutting workshops.
© BRGM - D. Dessandier
BRGM checks the quality and traceability of pieces cut in stone-cutting workshops.
© BRGM - D. Dessandier
After being checked by BRGM, the squared blocks, sawn on 4 faces, are made available to stone-cutting companies.
© BRGM - D. Dessandier
July 2021 - March 2024
The public entity Rebâtir Notre-Dame de Paris once again asked BRGM to optimise and secure supplies of hard stone from the Croix-Huyart site. This required an estimated 750 m3 of dressed blocks (ready to lay), which meant around 2,000 m3 had to be extracted from the quarry.
February 2022
BRGM acted as an intermediary between Rebâtir Notre-Dame de Paris and the Croix-Huyart quarry, which signed a private contract to supply the hard stone needed to restore the cathedral. Contrary to current practice, the stones would not be purchased from the quarry by the stone-cutting companies, but directly by the supervising contractor, who would then make them available to them.
February 2022
Based on the timetable for making the material available to the stone-cutting companies chosen by Rebâtir Notre-Dame de Paris and the architects, and in line with the overall schedule for the restoration work, BRGM defined a rigorous and innovative procedure for securing the supply of hard stone.
March 2022 - March 2024
During this period, BRGM carried out almost 90 inspections, after the raw blocks had been hewn and then sawn into large blocks, and during selection of blocks by the companies, and finally after the architectural elements had been cut.
7 December 2024
The official ceremony, attended by the President of the French Republic, began with the opening of the cathedral doors by the Archbishop of Paris. The fire-fighters, craftsmen and companies that helped save and restore the building were then given a long round of applause.
Our objectives have been achieved: in the cathedral, you can't tell new stone from old stone with the naked eye. And the restoration was completed on schedule.
Cover of Issue 29 of the Géosciences journal
© BRGM
Géosciences No. 29: Talking about Earth
“Talking about Earth” may seem to be a surprising expression for a scientific journal. However, it is by telling this story that the geological history of our planet is most clearly understood. And when faced with the amazing phenomena that led to the formation of the rocks beneath our feet, it is often wonder that dominates.
This 29th issue of BRGM's Géosciences journal takes a slightly different angle from its predecessors, exploring the beauty of the landscapes that surround us, inspiring the arts through science, passing on the Earth sciences to young people and the general public, and protecting our geological heritage.
