With some of the left over hemp, dad built a hemp clay oven! He used hemp inside the brick base layer between glass bottles. Then, the family got together to make the first layer of the oven with fire clay and sand (no hemp). After it was dry, we made the insulation layer by: mixing a thin clay slip; folding it into the dry hemp; making ‘cobs’ of clay-hemp mix; and building the insulation layer like round ‘bricks’ around the first clay layer. The insulation layer took one full, fun-filled day, complete with making mud pies and mess! (Don’t be fooled, though, getting the right mix of ingredients and building technique is not child’s play.) After it was dry, we made the final layer of clay and decorated it with a beautiful swirl!
We’ve had a few months break from building as we’ve been busy working at Sustainable Futures Australia and SIT World Learning. But now we’re back on the job, so look forward to a series of posts in the next few weeks!
The first thing we want to share with you is how we’ve encountered a few issues along the way, and made a few mistakes, but what is so awesome about this material is that you can just make up a small batch of the hemp-lime-sand mix and patch things up!
- Mistake #1 – Small holes were left in the hemp walls, reaching from one side of the wall to the other, where the bolts attaching the formwork had been. Fix #1a – If you intend to render, there is not problem as these small holes can just be covered by whatever render you use. Fix #1b – If you want to leave the hemp ‘raw’, then dampen the hole with a spray water bottle, poke a few pieces of the hemp from your hemp-lime mix directly into each hole with your finger, then tamp with a heavy block of wood so it matches the hemp wall around it.
- Mistake #2 – Some sections of the hemp wall were too loosely packed during the workshops, so are a bit crumbly. This is not much of an issue if you are rendering over the top. This was a real issue under some of the steel beams where it was difficult to reach and so there were actually holes in the walls! Fix#2 – Allow the wall to set for a week or so, remove the really crumbly bits around the large hole, dampen the area with a spray water bottle, pack the hole with hemp-lime mix, and cover with a small pice of formwork screwed into the hemp wall.
- Mistake #3 – During the tamping, one of the electrical conduits that was positioned inside the formwork was knocked out of place. The electricians were pretty pissed off! Fix #3 – They went searching for the conduit in the rock-like hemp wall with a hammer and chisel, and when they found it, bent it back into the correct position using a welding torch (!!). Such are the fire-proof properties of the hemp-lime mix, there was a flame thrower firing into the hole in the wall for quite a while without any adverse affects! When the conduit was back in place, we simply filled the surround hole as usual!
- Mistake #4 – Due to the speed with which we created the walls during the workshops, it wasn’t possible to create fancy formwork to create some of the shapes we wanted (eg., curved archways, bevelled corners). Fix #4 – Once it is set, the hemp walls can be shaped using a electric jigsaw!
- Mistake #5 (this one is a doozy!) – We waited 3 months for the hemp walls to cure properly before rendering. During this time, we went away for 3 weeks, and one cheeky pair of kookaburras dug a cave inside the 30cm thick wall. Fix #5 – It took more than a bucket of hemp-lime mix to fill! The external hole was quite small compared to the cavern within, so it was relatively easy to fill and render over the top. The kookaburras kept coming back though, leaving claw and beakmarks in the setting render!!
After the workshop participants left, a crew of carpenters from Xylosinuous joined us to finish hemping all the walls … right up to the top where the going got slow as we needed to tamp the hemp horizontally into the space between the top of the formwork and the bottom of the weatherboards. So, in total, it took us 5 days of teamwork to get the hemp walls up! After the last day of hemping, Sophie (of Upcycled by Sophie fame), created wonderful window frames around our old Federation windows; Xylosinuous carpenters created their signature curvy frames for the internal walls; and I patched holes in the hemp (left by formwork attachments and some dodgy workshop tamping under steel beams).
Our second workshop was filled, mostly with potential owner builders, with 22 of us onsite for another amazing weekend of building with hemp. The training was more intensive this time, as most participants were building novices.
And check out our youtube video clip, to get the feeling of how we were working together, and the constant soundtrack of Joel’s mixer!
Klara Marosszeky, ‘hemp building guru’ of the Australian Hemp Masonry Company, ran a full weekend workshop using our build for ‘on-the-job-training’. Participants learned about the nitty-gritty of hemp lime construction, including how to make ‘the perfect mix’ of hemp, lime binder and sand; how hard to ‘tamp’ the mixture down into the formwork; curing times for different purposes; OH & S issues; and council requirements. We built one third of our hemp walls! Everyone had lots of fun and ate great food! The next workshop will run in 10 days time, so click here to register.
Xylosinuous’ carpenter and builder made a solid timber stud framework to sit inside the hemp masonry walls. We sourced the recycled hardwood timber from The Big Shed in Maclean, which is a treasure chest of recycled building materials! Another score from the Big Shed were a stack of old steel chairs from a country hall (in the background of one of the pics). In terms of large scale recycling, though, the whole house above this extension is recycled! It was originally built in 1911 in Grafton (50kms away) and moved to this site 18 years ago when a block of flats took its place.