By Patrick Wagner
Aaron Schmidt, a journeyman plasterer, stares silently at a photo, trying to identify the type of plaster that was used to build the Asheville hemp house in North Carolina. His guesses sound like questions before he calls out to his partner for help. After several more wrong answers and moments of frustration, Schmidt and his partner decide the mixture must be a dismissible one-off brand.
The compound itself looks innocent enough. Faded green dust, with short dusty stems and smaller fibers that look almost like grass clippings that have been dried in the sun. The drying hempcrete blocks look almost like any other wet cement with just a slight greenish hue to them. At a glance, it’s indistinguishable from any other building materials.
Steve Allin, author of “Building With Hemp,” is a hemp guru of sorts. He believes industrial hemp is an untapped natural resource. Allin travels across the world teaching classes on hemp building and the benefits of using the plant as a tool for society.
“If you want to make a difference rather than just talking about the ecological problem we face as a species then we need tools to carry out this work,” Allin said. “Hemp is an amazing tool for these problems and being able to build houses free of toxins with little or no heating or cooling needs, then that’s what you should do.”
Although Schmidt has worked as a plasterer for nearly two decades, his inability to identify the hempcrete mixture wasn’t necessarily due to lack of experience or customer interest. More, it’s because the world of industrial hemp has been mired in legal contradictions for decades. Hempcrete is still suffering from the same national restrictions that have kept it a secret from plasterers like Schmidt; but with the way laws have been changing in the last few years, industrial hemp might become the nation’s all-in-one solution for the first time since marijuana prohibition.
Hempcrete is an alternative material for insulation and construction. The mixture is a combination of cement, lime, water and hemp. Despite the fact that hempcrete has a lower carbon footprint than concrete, the product has been a casualty of the prohibition of marijuana.
The simplest way to get your hands on hempcrete is by ordering it from a vendor or by attending one of the many hemp-focused seminars that have been growing in popularity. The recipe is simple enough to recreate on your own for construction experiments, and Allin pointed out there is no real need to purchase the finished product if you can create the mixture yourself.
“We need to be creating local versions to reduce transport costs,” Allin said. “I am positive that most existing recipes for the Hempcrete binder all perform in similar ways but manufacturers will always claim that their products are superior in some cases the only one that works.”
Because of its black market roots, the cost of hempcrete varies from vendor to vendor, but is still generally cheaper to produce as an independent contractor. However the advantage of using hempcrete is what you don’t have to pay for.
Contractors are normally required to heat concrete mixtures to roughly 3,000 degrees Fahrenheit to get the concrete to set. With hempcrete, contractors are able to set the mixture without having pay for such an enormous amount of energy and as an added bonus, they wouldn’t need to wait nearly as long either.
“We have discovered that the combination of hemp hurds (particles of the woody core of the stem created during the removal of the fibers of the outer skin) and a binder made from limes or clays, that unlike cement allow water vapor to move through it (hygroscopic) produces a masonry-like material that both insulates and stores heat,” Allin said.
Allin said he and his associates have discovered that the combination of hemp hurds (particles of the woody core of the stem created during the removal of the fibers of the outer skin) and a binder made from limes or clays produces a masonry-like material that both insulates and stores heat. Unlike cement, it allows water vapor to move through it, Allin said.
“These might not seem very valuable qualities in combination but it means we can produce a home that has the energy consumption of a ‘passive house’ without the need for layers of plastic or pumps to provide air supply,” he added.
These benefits are compounded further by the natural insulation properties of the lime-based mixture, which reduces the need for auxiliary heating and cooling by up to 60 percent. The malleable nature of the mixture allows it to be used in almost every part of a building’s walls and roof and due to this flexibility, contractors are not required to install expansion joints.
The self-healing properties found in hempcrete stem from the lime used in the mixture, which should be roughly 95 percent calcium. The calcium in the lime has a continuous hardening effect that slowly petrifies over time. This element allows constructs to heal with the passage of time, whereas concrete remains cracked and slowly degrades.
Another benefit of using hempcrete over concrete is that slumping and vibrating castings no longer factor into the construction time table. Slumping is a commonly known problem with concrete, where the mixture will shift or collapse under its own weight.
Unfortunately the benefits of using hempcrete do not extend to a building’s foundation below ground. Since the mixture is lime-based, prolonged exposure to moisture results in slow deterioration. Exposure to natural elements like snow and rain do not affect hempcrete walls and roofs, even if you live in a rainy climate like the Pacific Northwest.
The availability of hempcrete varies throughout the country. Although the mixture is legal to use in all 50 states, only a few states have allowed growing industrial hemp, and it is still illegal to import the seeds used to grow the plants in the United States. Contradictions like this have hampered the production of hemp since the early 20th century.
Buildings made from hempcrete can be found easily throughout the nation and the rest of the world. Unfortunately, the majority of these buildings have been built as a novelty or as a proof of concept and not as the serious long-term investment they could easily become.
Although several states have decriminalized hemp production, it — like its psychoactive cousins cannabis indica and sativa — remains illegal at the federal level with action from Congress.