Saint-Gobain wants to industrialize earth construction

"It's a world first that starts in France", announced Patrice Richard, director of distribution of the group: a mass program aimed at reusing from 2023 the earth excavated from construction sites, both to build houses single-storey buildings.

Originally, the group had been seeking since 2019 to respond to the request of one of the largest public developers in Europe, Euroméditerranée, which is piloting the renovation of the deprived neighborhoods in the north of Marseille.

"They told us: + The French government and standards require us to use wood and biosourced materials to reduce CO2 emissions from construction, but we don't have wood: what can we do with earth? Because we have land+", recalls Mr. Richard.

By combining its research strengths, its factories and its Point P materials distribution network, Saint-Gobain has imagined the possibility of filling wood-framed walls with sprayed or poured "earth concrete", or of building with concrete blocks composed of earth, a binder based on steel industry waste, crushed recycled concrete and plants such as hemp.

Ideas in Morocco

Apart from the fact that they are economical, cob or adobe houses, which are found from Morocco to Latin America via the Sahara or Yemen, have three qualities: they offer better comfort in summer and in winter, better hygrometry, and better sound insulation.

So many factors from traditional cultures that are highly sought after to adapt modern construction to global warming, while reducing the carbon emissions of the construction sector, weighed down by those of cement manufacturing. Cement alone emits three times more carbon than air travel.

Earth concrete, if it does not yet make it possible to build load-bearing walls, could also make it possible to reduce the consumption of sand, which is increasingly rare, underline its promoters.

"We went to Morocco to take ideas," says Mr. Richard. "What we couldn't replicate were walls as thick as there, and above all we had to find a less labor-intensive solution."

With the technique of projecting earth concrete into a wooden supporting structure, we end up with a "carbon negative" building, he says.

This technique should also make it possible to consume less energy to heat or cool the building since the earth has the capacity to store heat in summer (at least 15 hours), to slow down the cold in winter, to suck up humidity when there is too much, or reject it if the air is too dry.

"test" houses

"Provided you don't use it on the facade," nevertheless warns Manu Foucher, a facade designer who fears cracks and cracks due to drought, despite the hemp incorporated in the recipe to limit the shrinkage of the earth when it's dry.

In use, with a pump truck that fills the wooden frame with earth concrete, Mr. Foucher finds "that we save time on the site". Saint-Gobain is committed to launching training programs for artisans.

For the moment, a handful of "test" houses are planned in France and the group has signed two building projects whose construction should start in 2023.

On the cost side, the project "was nicknamed Dacia at the beginning", from the name of the low-cost car from Renault which proved to be a commercial success, explains Mr. Richard. "A wall supplied and installed should not cost more than a basic wall" in concrete, otherwise it could never take off, he emphasizes.

"Concrete manufacturers are not competitors, they are partners, because we help them to decarbonize buildings, and we cannot do without the portability of buildings (reinforced concrete foundations), but thanks to the earth we will be able to comply with the new French construction standards RE2020", hopes Michel Daniel, director of development and sustainable cities at Saint-Gobain.