The Hemp Clay Experience

We’re working in a home where we used a hemp and clay mixture between timbers to add insulation and thermal mass. Why did we choose this, and how is it different from the hemp-lime or hempcrete building processes?

Typical Hempcrete

Hempcrete, or hemp-lime, as you may know, is a popular form of wall infill that’s a mixture of hemp hurd, hydraulic lime, and water. As it cures, the lime in hempcrete chemically changes back into the same composition as limestone, making it rock solid. Frank has taught at a few hempcrete workshops around Colorado with John Patterson of Tiny Hemp Houses.

hemp building workshop
At a hempcrete workshop Frank co-taught at in Colorado.

The Good:

Hemp! It’s great. It grows fast, and needs less chemicals while growing: all reasons it may be more ecological than other building materials. Hemp is also better for soils than most other plants, with its deep roots that aerate soil. Additionally, the hemp stalk is composed of about 50% carbon by dry weight. This means that the carbon sequestered from the atmosphere during photosynthesis can be locked into our building like a carbon sink, not being released until the building is demolished much further down the line. This enables us the possibility to build a “carbon negative” wall system. If you’d like to learn more about carbon sequestering and building for climate change, we will be posting a blog soon.

The Not-So-Good:

Lime, while a natural and healthy building material, requires a lot of energy input to be created. Also, we import a lot of the natural hydraulic limes from overseas, increasing the embodied energy of the material. Alternately, a mix with cement is used, which also has very high embodied energy and accounts for an absurd amount of greenhouse gas emissions. There are other additives that can be mixed with lime to make it hydraulic, such as different types of pozzolans and geopolymers. These have their own benefits and drawbacks, but it comes down to manufacturing processes, local availability, and toxicity.

What about Hemp-Clay?

Colorado is blessed with beautiful and strong clay, an alternative binder to lime or cement. The best part of this is that the energy required to dig up and screen local clay is minuscule compared to burning lime.

We made a test brick with hemp hurd and clay slip, and the result was strong and lightweight – a perfect combination of insulation and thermal mass (especially once clay plaster is added).

The Installation

The hemp clay installation process went very similarly to hemp-lime. Forms were packed with wet material and then moved up. It goes pretty quickly if you can make your mix dry enough, but still sticky and workable. That way, forms are moved up and the packed in hemp-clay sticks in place without slumping.

hemp building process
Forms and the tamped hemp-clay mixture.

Drying

Since clay does not set chemically, like lime or cement, it has to dry naturally, with time. With several fans and dehumidifiers placed around the home, it still took a while to fully dry. We used a moisture meter to check deep within the walls, and later patched those spots where we had to put the probe in.

hemp wall drying
Hemp wall drying in the basement. Some forms had to stay up a little longer for extra reinforcement of thinner areas.

This step is very important because if you seal the hemp up with plasters before it’s dry, although it can still breathe through the plasters, there is a greater chance that some moisture will get stuck deep in the wall. Over time, this could lead to mold.

Another thing to note is the clay tends to shrink as it dries. This led to some cracking and pulling away from timbers. We took an extra half day to come back and fill those cracks in to prevent thermal bridges and loss of insulation in those places.

hemp clay dried
The dried hemp-clay infill shrunk and pulled away slightly from the timbers. Nothing plaster can’t cover.

Plaster Prep and Plastering

This step is again just about the same as with hemp-lime or hempcrete. We had a few places where the mix was too dry or didn’t have enough clay, as well as fragile corners around windows where we used an expanded metal lath to shore up the hemp clay. Landscape staples were used to attach the lath to the hemp, where needed.

We used clay plaster and our sprayer to get a base coat up first. The texture is perfect for plaster to stick to. Although clay plaster is the safest bet for a strong bond, a lime plaster or lime stabilized clay mix would also key in well to the rough surface.

hemp clay wall
Before
hemp plastered wall timber frame
After

We’re pretty happy with the results and process. It’s not too dissimilar to a woodchip-clay infill wall. The fact that it’s a low embodied energy and carbon sequestering solution is exciting, but the amount of time it takes to dry is a challenge. However, working in the summer could speed that up easily. We would also consider adding a small amount of cement or lime to the mix in order to create that chemical set and allow us to fill higher and faster.

We used a mortar mixer for mixing, which only allows a certain amount of minimum moisture. If you wanted the mix dryer, a horizontal drum mixer would be a better option.

Unsurprisingly, we’re not the first to try this. Check out Chris Magwood and the Endeavour Centre Blog below for their experience.  Scroll to the bottom if you just want to read the hemp-clay part. I think that the hemp-clay block shows the most promise. Because they are small, that minimizes the risks of cracking and pulling away that can happen during the drying of a large wall.

Hempcrete developments

Thanks for reading, and let us know your latest hemp building experience, or if you are interested in trying it out for yourself, or in your home, backyard studio, or shed!

Green and Low Carbon Building Interview

lime plaster skylight

Frank participated in a brief interview on green building in Colorado with Boulder, CO radio station KGNU. Both Living Craft and Rodwin Architecture were represented after our joint presentation at The Eco-Social Solutions 2018 conference at CU Boulder. Click below to give it a listen, and be sure to read the whole article at KGNU’s site, linked below.

Green Building and Carbon Reduction

lime plaster skylight

RMNBC 2017 Recap

Living Craft owners were recently proud to be speakers, sponsors, planners, and attendees of the 2017 Rocky Mountain Natural Building Conference, co-hosted by the Colorado Straw Bale Association and Common Earth. It’s been a fun and exhausting process through which we learned a lot, both about hosting a conference, as well as all the learning opportunities from speakers and other attendees of the event.

This year’s event was a blast, where we finally had a chance to meet other straw bale and natural building enthusiasts and reconnect with our mentors and friends from past natural building endeavors. The scope of the conference was broader than similar events put on by COSBA in the past, as we were striving to connect straw bale with other building techniques and ideas which can offer their own unique benefits. Speakers and attendees included earthen and adobe builders, hemp builders, building scientists and passive house experts, timber framers, architects, permaculturists, and landscape and greywater systems designers.

Frank was the emcee for the event, and Ben and Frank gave a presentation titled: Natural Building in the Urban Environment – Low Hanging Fruit. Cheryl was on a panel with several of her mentors and peers, discussing Intergenerationality in Natural Building.

Other highlights were Deva Racusin of New Frameworks Natural Design Build discussing building science and the important role of natural building materials and techniques in the green building movement. There is a huge opportunity for natural builders to promote building homes that not only have low energy use during their operation, but are also made of materials that sequester carbon within the structure of the building itself. By using plant based materials like straw, wood, cellulose, and hemp, instead of carbon emitters like steel, concrete, and mineral wool, the immediate carbon footprint of the building is significantly lower. This is absolutely essential to fight climate change in the moment, rather than waiting for benefits to offset inputs after 20-30 years or more. His business partner wrote a great article that goes into more detail about sequestering carbon in buildings.

The Friday night panel discussion with Deva, Mike Wird, Brian Fuentes, Emily Niehaus, and Derek Roff was also a really fun and informative discussion. The crowd was able to get involved by asking question via a website, which other audience members could vote on to lead the topic of conversation to areas of highest interest. Mike’s discussion of leverage points was inspiring and artful, as was Emily’s reminder that we all have more to give, as her upcoming role as mayor of the town of Moab illustrates.

An impromptu 5×5 panel on Saturday night allowed some of our friends for CASBA (California Straw Building Association) to share the results of wildfires on several straw bale homes which were impacted in recent wildfires across the state. We are truly impressed again and again by the durability of straw buildings with lime plaster, as several homes were left intact even after other non-straw structures nearby were damaged or destroyed.

Finally, COSBA and other anonymous donors, along with event attendees, were able to raise a significant donation to Liz Johndrow’s Pueblo Project, a non-profit that teaches local Central American people how to build with adobe and clay, and improve their homes’ durability, beauty, and comfort with these simple and affordable techniques. She’s hosting a natural building conference of her own in Guatemala this year.

There was too much fun to fully recount here, but Living Craft would like to fully extend our gratitude and love to our community for joining us on this amazing weekend. We hope to continue to work with all the folks we met and those we didn’t get a chance to talk with.

‘Til the next one, friends! #RMNBC2017