Notre Dame may take decades to fix. The first concerns are water and soot - what do restaurants use to wash dishes

There are two holes in the place where the vaulted stone ceiling of Notre collapses.
The 19 th century wooden spires of the cathedral and most of the roofs were gone.
Parts of the interior walls were blackened by the heat of Paris's most important fire in centuries.
With the world absorbing the great destruction of the Virgin hell, architects and engineers are expected to come decades later --
The long recovery process is full of unprecedented challenges.
Designers need to navigate through complex structural issues and subtle preservation debates to meet the needs of a range of stakeholders.
They all ask the same question: how do you recover 850-year-old icon?
"The whole world is watching and everyone has something to say," said Mark Walton, director of the Center for Arts Science Research at Northwestern University.
"It must be built in the next 1,000 years.
So it's going to be a different structure, but it's not necessarily a bad thing.
"The first thing is to get the cathedral dry," said John Federer, who served as director of heritage protection in Britain, a government agency that maintains the country's monuments.
"There are millions of gallons of water pouring into the building that will penetrate into the basement of the basement," said Feidler . ".
Before the whole building is completely dry, pumping may take months or even years.
"It's easy to make the surface dry because the surface has a lot of pores, but deep in the stone, the pores get narrower and it's hard to suck the water out," he said.
"When the walls remain wet, you produce mildew, mold, fungus, and salt crystals, which can break the pores in the stone and cause their surface to deteriorate.
"Soot is also a particularly worrying issue because it's too greasy, says Rosa Loinger, an architectural and sculpture administrator in Los Angeles.
"People's first instinct is to wash, but that's the last thing you should do," she said . ".
The limestone in this building is porous, so soap and water will bring the soot into its pores.
On the contrary, soot must be removed when drying.
"The earliest decision here --
Agreement taken
How successful such a project will be defined.
"When administrators address these issues, other teams will begin to address the biggest engineering challenge of the whole project: an assessment of the state of the structure of the cathedral.
Most of the analysis methods are tailored to modern buildings, not stone structures, so it may be difficult for engineers to determine the stability of the damaged cathedral, says Matthew Derong, professor of Civil and Environmental Engineering at the University of California, Berkeley, has worked in historical architecture research in Europe.
But the chapel must have been destroyed, says Frank Escher, an architect and protector at Escher gunwadner construction in Los Angeles.
"Fire of this nature will weaken the stone structure.
It's too early to say whether it's safe or not, "said Escher, who is currently recovering from the century.
The old church of the main festival, the oldest bishop Church in Los AngelesA.
As officials begin to stabilize the cathedral and remove damaged materials, attention will be paid to the upcoming reconstruction.
In order to evaluate the vaulted ceiling or vault of the cathedral, workers need to check the structure block by block.
They can then install the necessary temporary brackets.
If the upper part of the wall is unstable, the building may need large scaffolding to help withstand the weight. Since two-
The wooden roof of the cathedral has disappeared and the arched ceiling is exposed to elements.
That means the maintenance team needs a weather protection plan, Derong said.
The Reconstruction Design For Notre will be a highly collaborative process, including the representative of the Roman Catholic Church, the French government and the vast number of investors.
The process will require them to participate in a debate that has plagued the historical architecture community.
"Should you forge history or create something of our time?
Meredith Cohen, an art historian at the University of California, Los Angeles, said he is an expert in Gothic architecture in Paris.
These discussions can
She said it should be done.
Slow progress.
Cohen himself was in favor of a way to acknowledge the relevance of the building in the 21 st century, and did not favor a return to the 1100 plan.
In fact, it means not copying the iconic spires of Eugene Emanuel Violet's design --le-Duc in the mid-
1800, though it may be replaced by something new.
"Carbon Copy is a false history because you can't re-
Create the past, "she said.
"Its completion date is still 2019.
But Escher says sometimes it is appropriate to copy an original piece, just as it was rebuilt in Warsaw after World War II.
"The memory of the monument is very important for people who know about the building," he said . ".
"It is important, however, that people do not pretend that this is a real historical event.
A person has an obligation to be honest.
"At the moment, the focus is on" stabilizing the building and saving anything that can be rescued, "Lowinger said. ". Years later-
The long design process has been completed and the workers will begin to repair the vault masonry with stones, remove the damaged pieces and carve out new pieces that fit perfectly. Modern stone-
The cutting machine can shape the building blocks, but the bricklayer must be assembled manually.
Engineers often use modern materials and methods to repair historic buildings "for familiarity and convenience," Derong said.
But he warned that there might be fewer shortcuts.
The long term quality of the building, as seen in a cathedral reinforced with concrete, was later destroyed by an earthquake.
"It will certainly not provide long term
"He said.
"The solution is there;
This is just a long way to go.
The most important thing is that it's done right.
"How to replace the wooden roof of Notre can be tricky.
The vast amount of wood used on the original roof came from the 12th-century trees, which have been hundreds of years old.
"Where do you have 50-
300 acres of forest-year-
Is it OK for the old tree and the man who cut it down? ” Escher asked.
One option, he says, is to use engineering beams made of a fusion of multi-storey wood, a modern invention that has a greater strength and a longer board than a board made of natural logs.
No matter what material is used, the roof must be heavy and the structural engineer needs to calculate carefully to determine how much weight the walls of the cathedral can withstand.
"Things like this can take years," Escher said . ".
"Things like this can't be rushed.
Ms. Loinger said she was optimistic about putting enough resources into the project.
French tycoons, companies and ordinary citizens have already paid about $0. 7 billion for repairs.
There is a silver lining.
Despite the large amount of falling debris and hot heat, the three medieval rose windows set in soft lead seem to have survived.
This large organ, consisting of about 8,000 pipes, has water damage but is expected to recover completely.
The reconstruction of Notre could prompt engineers, environmental activists and other types of experts to invent new technologies that will be used in other projects, losingh said.
"With a website of such a cultural scale, there is a willingness to have talent," she said . ".
"The best solutions will come together and we will all learn from them.
King Wilcher, a special correspondent in Paris, contributed to the report.