What will save the Notre Dame? (2)

-read part 1 of this article here-

A very short time frame (2)

So President Macron has announced that the cathedral should be rebuilt in five years. He has appointed a French general to run the whole operation and there has also been announced that there will be a competition for a new spire. I guess it will become something made of steel and glass, with a modern slightly pyramid-like shape… oh wait, where have I seen something like that before?

All very remarkable. A number of well-informed decisions to be taken are pushed through quickly without discussion or consultation, and deploying the military renders the freedom to bypass a lot of rules. For yes, there will be needed a huge flow of materials (for the roof alone, more than 1300 thick straight oak trees are needed, and wherever would you get these from on such short notice? Fortunately British estates have already pledged to gift a few hundred of those.)

Logistical challenge

The advantage of management by a general is of course that he will be trained in military planning. He will have a thorough knowledge, or have at least access to people who can do it, of huge logistical flows on a scale that is uncommon in everyday life. I don't expect this general to be familiar with all the ins and outs of the restoration of a Gothic cathedral; for that there will be other people . He will be the person to take care of the basic conditions.

There are also huge amounts of new stone to be quarried, which will have to be processed in many different places and all brought to the cathedral at the right time. Luckily it's the right on the banks of the Seine, so just as in previous centuries, the material can be supplied over the water, so the city won't become clogged with trucks. Of course they'll need a jetty for unloading with a crane system and a large storing facility, but the Dutch among the readers know only too well that you can make that space yourself.

France has many quarries that supplied stone for the construction of churches in the past. There is a huge variety of natural stone, from granite, basaltic lava and hundreds of types of limestone to sandstone and gneiss. But not every stone, and not even all stone layers in the best quarries, are suited for church construction. Add to that the fact that currently many quarries have a relatively low production or even lie dormant, it becomes clear that a lot of them will have to be scaled up. Suppose a quarry has excellent material, but there is still quite a thick layer around it of lesser material. It will take some time before this quarry can supply the right material.

And that's not even mentioning the wooden roof, the roofing material, all the windows, all of the sculptures in bronze and stone, all of the ornaments, and where to get all the professionals from. And how they all get there.

The roof of a gothic church

cross-sectional view of the buttresses and flying buttresses

What has been lost now? Most striking is the disappearance of the wooden roof and the central spire. Now the roof of a Gothic church consists of two parts. First there is the stone vault which you can see from the inside, and this is covered by a wooden roof construction that carries the slate or, as in the case of the Notre Dame, the green copper roofing.

Imagine you open a book and put it upside down, like a roof, upon the table, with its pages to the inside. The book will want to sag outward and lie down flat, unless you stop that with your fingers to the sides. It works similar with such a roof: unless you provide back pressure to the sides or add a tensioning bar through the middle, it will want to lie flat. Since no tension rafters were used in the Gothic, but pointed arches instead, the outward pressure had to be taken care of from the outside. In the past, this was solved by building meters thick walls, which made large buildings very dark inside. The genius of the Gothic builders is that they designed open structures that supported the walls from the outside: the buttresses and flying buttresses. The walls therefore don't need to be massive anymore, and allow for huge windows.

At Notre Dame all 1300 wooden rafter beams of the roof have disappeared, and the underlying stone vault below has partly collapsed. A vault is a set of pointed arches that remain in place under their own weight, thanks to that pressure from the outside. The (triangular) spaces between said pointed arches is filled with masonry, so you end up with a stone roof: the vault. If you want to bring back the lost parts of the vaults of Notre Dame again, you'll need to put it back stone by stone. It is a self-supporting construction,, so during the build a heavy wooden support will have to carry the load: the so-called forms.

Once the vaults have been restored, the rafters can be built up again. This can be done with green wood if necessary; that has happened in the past, only one must take the shrinkage into account. I do not know if they do it like that nowadays as well or prefer to use dried oak. I have no knowledge of this work, but it is certainly a huge job to tailor all the wood joints and put them all together on site. Not even mentioning the wooden, lead-lined spire designed by Viollet-le-Duc.

The windows of Notre Dame. Photo by Lionel Allorge – CC BY-SA 3.0, Wikimedia Commons

The windows of a Gothic church

Tracery on the Chimera Gallery of Notre Dame. Photo by Parsifall – Own work, CC BY-SA 4.0, Wikimedia Commons

In the Middle Ages there was no technique yet to create large glass surfaces. Small panes of glass were made by turning round discs, and then cut to size. To put together all these loose pieces they were encased in lead profiles: hence glass-in-lead: stained glass windows. But don't be mistaken: glass art was at a very high level, both technically and artistically. The large glass surfaces were used to depict colourful scenes of biblical stories and saints. These windows have a wrought iron frame and an often wrought iron cross bar: a tension rod which should give support across the middle of the window , so that the window doesn't flex under wind pressure, and becomes one rigid unit.

The window's frame is made up of profiled natural stone. In fact, the whole window is a combination of stone, iron and glass: long slender stone ribs (bar tracery) divide the window into high vertical sections. At the top of the window, these join together into an ornate stone frame, the tracery, which has many creative shapes. Between the vertical bracing and the stone tracery at the top, the lead frames of the glasspanes are set into the stone notches..

It will be clear that a Gothic window is also very vulnerable. It is for many a wonder that the crown jewel of Notre Dame, its large rose window on the entrance side, has been preserved. Usually, the windows will be completely disassembled during thorough church restorations: all the glass panes are taken out by the glazier, cleaned up, repaired, and set in new lead frames. Often the stone vertical dividers will also be replaced and sometimes even the tracery at the top is copied into new stone, when the stone has deteriorated too much. Also, the iron bridge rods are removed, because they tend to corrode and crack the surrounding masonry. They are usually replaced by new bronze bars. Then often the remaining iron work is then mostly carried out in bronze or stainless steel.

Finally, everything is brought back. I've seen in many churches that the glazier also inserts panes of thick flat glass to the outside, to protect the stained glass and insulate it. However, a stained-glass window is never airtight, so it is extremely important that this front glass can breathe, to prevent accumulation of moisture behind it.

Now Notre Dame has quite a backlog in restoration. So if they want to do this properly, they'll really need to take on all of its windows. By the dozens. Where do you get all these glaziers from? And expert restoration contractors to remove the stone and iron work?

The drainage of a gothic church

gargoyle of the St. John's Cathedral in Den Bosch, copy new sandstone

Traditionally cathedrals have no modern downspouts. The water would have flushed off the roof into a wide stone gutter at the bottom of the roof, often behind a railing so that one could safely walk through the gutter. Later, many of those gutters have been lined with lead to prevent leakage.. Out of these gutters, water had to be carried far away from the walls. For that, there were two solutions: either it ran directly from the chute to the outside, or it was fed further out via a gutter on top of the flying buttresses. The end of the water outlet stood out from the walls for some distance and was often decorated with a monster head: behold the gargoyles. They spat the water out from the walls when it rained hard. Later on, often downspouts were still added, and the gargoyles just remained as a decorative element.

Often a church was topped with roof slate tiles: these lasted for a long time, and water was easily shed (from a slate roof, as is said). But Notre Dame had a beautiful copper roof, that was patinated green. But even a copper roof has a finite life expectancy, and I assume that roof was in need of a thorough inspection as well. Now no longer needed; a completely new roof, roof joists, and partly even vault will be needed.

Natural stone

Baldakijn voor de Sint-Janskathedraal in 's-Hertogenbosch in Udelfanger zandsteen

Canopy for the St. John's Cathedral in 's-Hertogenbosch in Udelfanger sandstone

A Gothic church is mainly built from stone. In the Netherlands, often the core of the walls are made out of brick, with a skin of natural stone blocks. But in France, where so much stone is available, many churches are constructed entirely of natural stone. In gothic architecture, practical construction and decoration go hand-in-hand inseparably with each other. Walls have moldings, where often leaf motifs are carved into, buttresses crowned with high pinnacles which are richly decorated with small crockets, flying buttresses have large leaf shaped ornaments, and everywhere you can see gargoyles, statues of saints, angels, reliefs and ornate portals. As described above, even the window frames are masterpieces of ingenious design in stone.

If in such a large church a hot fire is raging, the stone will become strongly heated. After a long heating with temperatures above 900 degrees Celsius, limestone disintegrates into calcium oxide (quicklime) and CO2. Although the fire at Notre Dame has not everywhere been so hot, it should be clear that the surrounding stonework sufferd severe damage and will partly have to be replaced. The stone in any case is not compact or reliable anymore. In addition, the church also suffered water damage and therefore will be at risk from fungus, and salt efflorescence corrosion in the anchorings, by which the anchors will expand and will destroy the stone later on. Finally, a lot of the stonework has been suffering so much from centuries of weather influences that many parts will have to be replaced.

Professionals needed

Stonemasonry blocks are essentially of an accumulation of geometric shapes. In exceptional cases I sometimes carve some parts of that as well.

For the restoration of such an extensive damage, hundreds of tons of processed stone will heave to be provided. Profiled blocks, blocks which only need a finishing chiseling stroke, sculptural parts, ornamental work, canopies, finials, and so on. The point is, it would take a few months for a stonemason to carve an intricate canopy. What do you do when you need to make hundreds of such blocks? France has far from enough masons who are doing this work at this moment. In addition there are even less highly specialized stonemasons, who can also make the most intricate work.

I expect that much of the work has to be contracted abroad. In France, the workload fell sharply for the stonecarvers by shrinking budgets for restoration. Less work means less stonemasons, it's as simple as that. Likewise, in the Netherlands a veritable bloodletting has taken place among stonemasons since about 2010, when several major restoration projects ended and companies had to let people go because of the crisis and the reduced number of projects. Older stonemasons have also stopped and never been replaced more. And in other countries that has taken place to a greater or lesser extent as well. I myself have been unemployed from 2010 to 2013 and had little work after that, until things finally got better in 2015. If there is such a gap between projects, many professionals will not return to their stonemasonry job.

tiny but very also large ornaments

Now I'm not a stonemason but a restoration sculptor. A restoration stonemason makes all the work that can be scribed with templates and can be drawn with construction lines. A sculptor makes the work that begins where the stonemason stops: ornaments and statues. Of these people, there are even less skilled craftsmen to be found. As far as I know, my three colleagues and I are the only ones still making sculptural work full time for churches and castles in Netherlands. In other countries, there are not many more of those. The French will need each skilled craftsman they can find, to complete this work so quickly.

Digitization of the process

picture of Thomas Aquinas to St. John's Cathedral in 's-hertogenbosch, currently in progress

Now time has not stood still since the Middle Ages. The computer age made its entry, even in traditional restoration. Already, all major stone processing plants own large CNC machines that can perform completely computer controlled cutting and milling. There are big five-or seven-axis milling robots which, with sawblades and routers that they can pick themselves completely unsupervised, can mill an entire sculpture from a block of stone. It seems like the solution. But it is obviously not all so simple. These robots first need prompts. Suppose, I want to copy an existing sculpture. Then I will have to scan the sculpture and enter that information into the computer and edit it into a usable virtual 3D image. Next, the scan should be checked for imperfections and those will have to be removed. Finally, a set of tasks will have to be assigned to the machine, the steps along which the robot can start milling out the sculpture from coarse to fine. In sculptures, or in blocks that are unique, this sequence needs to be repeated for every single block or sculpture. And then the stone block must still be loaded onto the machine and calibrated.

After milling, there are still a lot of details that the milling robot could not finish. It sure saves a lot of work for a sculptor, but here too, the hand of the artisan will still be indispensable. Indeed, unskilled finishing of such a sculpture can still totally ruin it. Stonemasonry blocks can be addressed that way as well, but there always comes a point where it is much faster and cheaper to have the final steps done manually by a skilled craftsman, than letting the robot slog on for days with a needle point endmill. And sometimes the machine can simply just not reach every nook and cranny, where a stone chisel can. In short, the skilled craftsman will still be necessary. And the main argument is that everything looks as dead as a doornail when it's all drawn with the computer and milled with the robot. "It is the hand of the craftsman that has to bring it to life', said a stonemason last all.

-Read more in Part Three: what are the possibilities, where lie the opportunities, what is the future and what will be the rescue of the Notre Dame?-

Follow me on Instagram↑

Beeldhouwerijblog.nl is the blog of Koen van Velzen, sculptor in stone and bronze. Look up my website as well: beeldhouwerijvanvelzen.nl

and Twitter↑

and on YouTube↑

Leave a comment

The email address will not be published.