A Name on the Eiffel Tower Belongs in Every Hempcrete Wall
- Shawn Ledig
- Aug 12
- 9 min read
How a French engineer who gave away his greatest discovery ended up at the center of our industry
By Shawn Ledig | U.S. Hemp Building Association
Seventy-two names are engraved around the first level of the Eiffel Tower. One of them built the foundation of modern hemp construction.
In my last piece, I traced hemp building back more than 1,500 years, from the cannabis-laced plaster of India's Ellora Caves to the old stone bridges of Normandy. This is the next chapter, and it runs through a single French name that structural engineers say almost every week without knowing whose it is.
Go to Paris, stand under the Eiffel Tower, and look up at the frieze that runs around the first level. Gustave Eiffel had seventy-two names engraved there in gold letters, honoring the French scientists, engineers, and mathematicians whose work made the modern world possible. Fourier is up there. Coulomb. Foucault.
So is Louis Vicat. And if you build with hempcrete, you owe him more than you probably realize.
The Man Who Solved Lime and Refused to Profit from It
Vicat was a civil engineer, trained at the Ecole Polytechnique and the Ecole des Ponts et Chaussees. In 1812 he was assigned to build a bridge over the Dordogne at Souillac, and that job pushed him into a question nobody had properly answered: why do some limes harden under water while others fall apart?
By 1817 he'd cracked it. He published the first scientific method for producing artificial hydraulic lime by calcining controlled blends of limestone and clay. He'd worked out the chemistry of modern cement several years before Joseph Aspdin patented Portland cement in England in 1824.
Then he did something almost nobody does. He published it and refused to patent it, considering the discovery a gift to the public. It made him a national hero in France. It also made him considerably less rich than Aspdin.
His name survives in every materials lab on earth through the Vicat needle, still the standard apparatus for measuring cement setting time. Every structural engineer in the world has run that test. Most of us never learned whose name we were saying. I hadn't, until I researched this piece.
Why This Matters to a Hemp Wall
Hempcrete is two things: hemp hurd and a lime binder. The hurd gets all the attention because it's the part that grew in a field. But the binder is what makes the wall a wall, and the binder is Vicat's territory.
Hydraulic lime is what makes a hemp wall behave like one. It sets and gains strength while staying vapor open, so moisture moves through the assembly instead of getting trapped inside it. It carbonates slowly over decades, pulling carbon dioxide back out of the atmosphere as it cures. Ordinary Portland cement does none of that well, which is exactly why it's the wrong binder for hemp.
The company Vicat's son Joseph founded in 1853 is still operating today, and still produces Prompt natural cement, burned at low temperature from a single limestone quarried in the Chartreuse massif near Grenoble. It sets in minutes, which is where the name comes from, and it built much of nineteenth-century Grenoble and Lyon. It's also one of the proven binder systems in European hemp construction, and it's the benchmark American formulators are still measuring against.
Hurd and lime. The crop is ours. The binder chemistry is two hundred years old.
Then a Mason Put Hemp into It
Vicat gave the world the binder in 1817. It took another hundred and sixty-nine years for someone to put hemp in it.
In 1986, a local artisan named Charles Rasetti was hired to restore the Maison de la Turque in Nogent-sur-Seine, a small town in the Aube region of northeastern France. The house was a 16th-century timber and earth structure, notable mostly for a passing mention in the writing of Gustave Flaubert. By the 1980s it was falling apart.
Rasetti wasn't an engineer. He was a tradesman with a problem every restoration mason knows: what do you put back into an ancient oak frame that'll insulate the building, let it breathe, and not destroy the timber you're trying to save?
The Champagne region had been filling timber frames for centuries with mixtures of rubble, straw, and lime. Rasetti substituted hemp hurd into that old vernacular recipe. Hemp was a regional crop in the Aube, and the hurd was a byproduct with no particularly valuable use. He reached for what was around him.
That building is where hemp hurd was first used as infill in a timber structure, and the work was completed in 1986. Everything our industry does today traces back to that wall.
The Forty-Year Proof
Here's the part that matters most in a code hearing.
In November 2024, Steve Allin of the International Hemp Building Association traveled to Nogent-sur-Seine to inspect the Maison de la Turque. Thirty-eight years after the original application, he found the hempcrete in sound condition behind its lime plaster facade.
Not an accelerated aging test. An actual wall, in an actual occupied building, opened up after nearly four decades and still performing.
Every new material faces the same question from builders, lenders, insurers, and code officials: how do you know it lasts? For hempcrete, there's a house in France that answers it.
From Repair Job to Industry
What happened next happened fast. By 1989, the first purpose-built new construction using hempcrete over a wooden frame went up in France. By 1990, Yves Kuhn had developed a movable form system that made it possible to build entire houses out of the material instead of patching individual panels.
In four years, hempcrete went from a restoration technique to a construction method. France then spent three decades building what an industry actually requires: professional rules, industrial hurd supply, binder formulations, trained installers, and real academic research.
Two Hundred and Seven Years
Put the whole arc in one line.
In 1817 a French engineer gives away the chemistry of hydraulic lime. In 1986 a French mason puts hemp into that binder and proves it in a wall. France industrializes the method through the 1990s and 2000s. And in 2022 the International Code Council approves hemp-lime for the U.S. model code, published in the 2024 International Residential Code as Appendix BL, the first time hempcrete appears in an American residential code.
Two hundred and seven years from the binder to the building code.
That last step is the one our members did. The appendix didn't appear on its own. It came from years of testing, documentation, hearings, and people showing up to argue for a material that most code officials had never heard of.
The American Chapter Is Being Written Right Now
That is where the French story ends and ours begins.
The second half of this history is being built as you read this, in Louisiana and Pennsylvania, Texas and Colorado and a dozen other states, by people whose names are not engraved on anything. And here is the problem with that: when an appraiser asks whether this has been done before in the United States, or a lender asks what these buildings are worth, or a code official in a county that has never seen a hemp wall asks who else has permitted one, our industry answers with anecdotes. France can point to a house in Nogent-sur-Seine. We should be able to point to a hundred addresses in our own country.
So this blog is going to build that record, and I want to tell you exactly where it is going.
Two more pieces will finish the history: how France turned one mason’s repair job into a regulated industry with graded shiv and professional rules, and how the material crossed into the English-speaking world and finally into an American code book. Then we come home. We will start with the U.S. projects already registered with this association, one at a time, with the full record behind each build: the jurisdiction, the permit path, the wall assembly, where the hurd came from, what it cost, whether it appraised, whether it insured, and who the building official was. Then we will introduce the people doing the work, because the American names in this story deserve to be attached to specific walls in specific counties.
And then we get to the hard part. Once you have looked at a few dozen American buildings honestly, the pattern in what is missing becomes impossible to ignore, and that is where the last stretch of this series is going: what our industry actually lacks, and what it will genuinely take to put hempcrete on the same footing as hemp wool and the other hemp building products that are already moving through ordinary supply chains. That is not a comfortable set of articles to write. It is the one that matters.
If you have built with hempcrete in the United States, I want your project in that record. Write to me.
The Gap We Have Not Closed
I am not going to spend the rest of this piece on that argument, because it deserves its own. But it is worth naming here, so you know what is coming.
France didn't get here on enthusiasm. It got here on infrastructure. Graded hemp shiv produced to a published specification. Binders with evaluated compatibility for plant aggregates under the Construire en Chanvre professional rules. Block manufacturing at industrial scale. Trained installers. Designers who can specify the material with confidence because somebody else already did the testing.
We have passionate people, excellent demonstration projects, and now a code appendix. What we don't have is factory production.
That’s the honest assessment, and it’s not a criticism of anyone in this association. It’s a description of where we sit in a sequence France worked through over three decades. Until a builder in Ohio or Louisiana can order graded hurd and a certified binder the way they order lumber and mortar, hempcrete stays a specialty product. No binder, no hempcrete. No manufacturing, no industry.
We are standing in the middle of that sequence. We will take it apart properly later in this series.
What I Take from It
I've spent the last several years on the American end of that arc: designing and building with hempcrete, bringing the process into Louisiana, and working through this association to move the material into our codes.
What strikes me is that none of the people at the front of this story set out to build an environmental product. Vicat was trying to build a bridge. Rasetti was trying to fix a wall. The carbon math, the moisture performance, the healthier interiors, the domestic fiber supply chain: all of that is real, and all of that came later.
They were solving problems in front of them with the materials around them. That's still the job.
So, the next time someone tells you hemp building is a fad, tell them the binder chemistry is two hundred years old, the oldest wall is still standing in France, and the man who made it possible has his name in gold letters on the Eiffel Tower.
Bring Your Questions
That's the conversation I want to have with you.
The Board and I are scheduling a members call soon, and manufacturing capacity is going on the agenda as a real discussion item rather than a comment at the end when everyone is tired. We'll answer what we can live on the call. What we can't answer there, we'll take up here on the blog and in the newsletter.
Send your questions ahead of time so we can come prepared with real answers: shawn@ushempbuilding.org
It's been too quiet. That's on us, and we're fixing it.
Shawn Ledig
Shawn Ledig is a structural engineer, President of the U.S. Hemp Building Association, Board Chairman of the Louisiana Industrial Hemp Promotion and Research Advisory Board, and founder of Delta AgroFiber Solutions LLC in Mandeville, Louisiana.
A Note on the Historical Record
Some accounts describe Charles Rasetti as the sole inventor of hempcrete. Others note that several artisans in the region were experimenting with similar infill approaches during that period. Rasetti and the Maison de la Turque represent the documented first application, which is the more defensible framing in a technical or regulatory setting.
Sources
• International Hemp Building Association, “The First Hemp Building.”
• BRANZ, “Hemp Construction.”
• Contemporary reporting on the November 2024 IHBA site inspection at Nogent-sur-Seine.
• List of the 72 names on the Eiffel Tower (VICAT, southeast face), via the official Eiffel Tower site and Wikipedia.
• Vicat, technical documentation on Prompt natural cement and its compatibility with hemp shiv under the Construire en Chanvre professional rules.
• International Code Council, 2024 International Residential Code, Appendix BL Hemp-Lime (Hempcrete) Construction (approved 2022, published in the 2024 edition).
Shawn, I am so enjoying your articles on the history of hempcrete! Thanks!