Innovation: Walls and foundations made from sprayed hemp-lime concrete
— La Maison du 21e Siècle
HECO (Hemp Engineering Carbon Zero) was founded last May by two engineering graduates from École de technologie supérieure, Philippe Fortin and Maxime Saint-Pierre. They plan to bring sprayed hemp-lime concrete to market this fall and will launch their flagship product this spring: prefabricated wall panels or blocks made from lime-bonded concrete and hemp insulation. “Since hempcrete takes up to two months to dry (about one inch per week), prefabrication will limit drying time on-site,” explained Philippe Fortin in a phone interview.
Hemp and lime are eco-materials particularly suited for foundation insulation because they allow water vapor to pass through, letting damp walls dry, he added.
A durable concrete
The qualities of hemp
Hemp is a bio-based material with a high saturation point, meaning it can absorb a large amount of water relative to its weight before dripping, Philippe adds. “It’s like a sponge, unlike mineral wool, which must be kept from condensing moisture. Breathable materials like hemp and lime prevent condensation by continually absorbing and releasing humidity. Thanks to its water retention, hemp reduces the humidex factor in a building, which also adds to comfort. Its hygrothermal qualities [the interaction of temperature and humidity in indoor air] have a big impact on how heat feels in summer: it’s not stuffy, and you don’t need air conditioning, which contributes to global warming due to refrigerant gas leaks.”
HECO Innovation uses the Belgian-formulated lime product Tradical, which includes hydrated lime and a bit of clay to help release humidity while offering strong compressive strength. “In two years, we hope to release our own version made with local materials.” Sprayed hemp-lime concrete costs between $2 and $3 per square foot per inch of thickness, depending on the complexity of the application—for example, in a hard-to-access crawlspace. “It’s complicated—you have to control the spray with 240-volt machines. We also hope to eventually build our own equipment.”
The Laval construction site
Émilie Lemay Bélisle and her husband, Christian Casilimas, own a home built in 1928 with a basement floor about 28 by 28 feet and only 4 feet 10 inches of headroom under the beams—5 feet 2 inches between them.
“We chose to use the space for storage, the laundry room that was already there, but especially as a play area for the kids,” explains Émilie. Water was seeping through the walls, which are partly made of fieldstone. The work was done last summer, but due to lack of time, a waterproofing membrane will be applied from the outside this year.
“We decided to spray two inches of hempcrete onto a small inner wall built against the three dampest foundation walls. The upper parts of the walls were insulated with hemp wool, which is cheaper. We built the wooden framing ourselves, which was then filled with sprayed hempcrete and hemp wool.”
“At NovEnviro, we recommend putting a breathable Salola membrane on the foundation before adding batt insulation or hempcrete,” notes Nicolas Séguin, VP and cofounder of the eco-materials distributor.
The hemp wool, the hemp-lime concrete, and its application cost around $8,500. After spraying, the rough finish needs to be smoothed out with a hand-troweled finishing coat of hemp-lime plaster. That cost a little over $2,000, including labor.
“We know we went with lesser-known materials and a technique that’s still developing, but we’re happy with our choice—it’s healthy and eco-friendly and aligns with the vision we had,” concludes Émilie.
Jean-Sébastien Matte and Gaelle Fedida own a 3,000 sq. ft. Montreal home built around the same time, in 1930. The former duplex was converted into a single-family house with two basement studios totaling 1,000 sq. ft. When their tenants left, Jean-Sébastien opened up the walls and discovered a damaged rubble foundation on a cement base. He cleaned everything, waterproofed it, and even installed a French drain.
He also chose hempcrete for its eco-friendly and aesthetic qualities. “Drywall didn’t really appeal to me. It’s ugly—it lacks character and life. I only used it for the ceiling.”
He had three walls insulated; the fourth had already been done during a previous renovation. It took four days to spray 4 inches of hempcrete on two walls and 2 inches on a shared wall. The total cost was about $14,000, not including finishing, and it took two months to dry. Jean-Sébastien estimates polyurethane insulation finished with drywall would have cost less than $8,000.
He’s finishing the walls during his spare time. Gabriel Gauthier, owner of Artcan – Hemp houses, a Quebec pioneer of this eco-material since 2010, supplied him with 32 buckets of premixed hemp-lime plaster. “You have to smooth, smooth, smooth and go over it again and again!” he says. “But the result is very satisfying. It creates a warm ambiance and great sound insulation. You feel wrapped in it—everything is well sealed around doors and windows.”
Craftsman Gabriel Gauthier explains: “We recommend using membranes and even an air gap between the concrete wall and hemp wool insulation. That can also be done with hempcrete. That said, applying hempcrete directly to the interior of stone or concrete foundation walls gives impeccable results that speak for themselves. It’s because the material is highly mineral and limestone-based. Only direct water infiltration can affect its appearance. So personally, I’m not worried about capillary action with well-mixed hemp-lime plaster applied to interior foundation walls.”
The space features a radiant floor heated by a pellet boiler from Austrian giant ÖkoFEN, the Pellematic 20 model from Maine Energy Systems. Certified by the U.S. Environmental Protection Agency (EPA) for fine particle emissions, the system cost $20,000 but consumes less than $3,000 in pellets per year—compared to $6,000 in heating oil per winter before. The slab is insulated with polystyrene: “Hemp isn’t recommended for floors,” notes Jean-Sébastien Matte.
A winemaker and cider maker, he’s very proud of his basement. “This work is done for the next hundred years. Maintenance and repairs are easy, and it regulates humidity, temperature, and sound. It’s a win on all fronts.”
And even when it comes to suppliers. “DEUXMAX [NovEnviro] are good people—but there’s no competition to drive prices down. Hemp costs twice as much as mineral wool. The only good law Donald Trump ever passed was the one legalizing industrial hemp cultivation. I’m hopeful it’ll open up the market!”