Plans were drawn and ready for Council, but first I had to make sure that Hemp Lime Masonry construction was manageable, affordable and aesthetically pleasing. My opportunity to do this came with a workshop conducted by Klara Marosszeky, from the Australian Hemp Masonry Company, held at Mountain Top 45 mins north of Lismore in early October 2011.
The workshop took place at Auntie Liz Johnson’s property where workshop participants had the opportunity to build the floor and walls of the post and beam Aboriginal Cultural Field Study Centre. The setting was beautiful we were surrounded by tall trees, birds, goannas, and wallabies as well as ticks and leeches. The workshop participants came from Sydney to Brisbane and points in between, from farmers to professionals, all with a common interest in the use of hemp as a building material. Some were keen to grow hemp and others to build and the weekend was a great opportunity to forge links between producers and consumers of hemp fibre.
When we first saw a sample of the hemp masonry many were surprised at how hard the material had set. The hemp fibres were completely in the lime based binder but air gaps were evident that would contribute to the materials insulating properties. Klara showed the group the hemp stalks and various processed fibres. The hemp fibre used for building was more the texture of playground mulch, than what you think of when you hear the word fibre.
The floor of the Aboriginal Cultural Centre was also to be made of hemp masonry. Prior to the workshop drainage had been installed under the floor and a layer of crushed rock placed between the concrete strip footings. The pole framing of the building and roof rafters were also in place.
Once we placed the geotextile layer, and after putting on our safety masks and gloves, lime is not good for the lungs or skin, the group launched into mixing batches of hemp masonry, pouring and tamping it in place, under Klara’s instruction. We mixed the material in a loud diesel pan mixer, it mixed large loads at a time but it was disappointing to learn that such mixers are not readily available in Australia – Klara’s being the only one for hire and specifically modified for hemp building. The hemp and binder had been conveniently bagged into batch sizes, so the mix was made up of one bag of hemp fibre, water, one bag of lime based binder, and sand.
Klara reinforced the need to get the mix “just right”, which was the texture of damp muesli. When the binder was first added the mix looked too dry, but when mixed it combined surprisingly well. Throughout the weekend there were lots of comparisons of hemp building to cooking and food preparation and by the end of the weekend workshop participants could tell if a mix was too wet or dry - having made lots of mixes over the weekend. We also learnt to watch out for “balling”, when the binder clings to the sand rather than the hemp fibre and forms hard balls.
After mixing the other job was to tamp the hemp down, using specially made tampers - a handle on a block of wood. Unlike rammed earth just a light tamping was needed and the mix was slightly springy preventing it from being jarring on your arms.
At the end of a day of floor placing the sky opened up and the rain poured down as tarps were tied down to keep our hard work dry. After dinner, cooked on the fire, the group chatted about the days experienced and Klara spoke to the group about growing hemp, answering all the diverse questions the group put to her. We then retired to our tents for a night on the Mountain Top.
A warm sunny morning full of birdsong, a hearty breakfast and it was off to work again - this time starting on the walls. The building was a natural pole frame house and the walls were to be 300mm thick to take account of the varying thickness of the poles. Klara also tried a new method of formwork using threaded rod to join the formwork together. This took a little bit of tinkering to get right, but once the first section of formwork was in place the team got mixing.
The hemp was bucketed into the formwork and spread out to form 5 cm layers. Each layer was then tamped, using both large and small tampers. The small tampers were used first to tamp the edges and around any protrusions like the posts or a stud, then the larger tampers, that had been specifically designed to fit just inside the width of the wall, were used to tamp across the whole width of the wall.
I had a good, but tiring, weekend and definitely learnt a lot, including the hard to describe “just right” texture of a good mix. The weekend also helped me confirm that I would make my house out of hemp. The only disappointment was that the formwork would have to stay on until the following day and we could not see the product of our hard work. This was overcome with some promptly e-mailed photos. Tara Jones is making a film about hemp farming at Ashford and has further photos of the workshop on her blog www.hemptheashfordtrial.blogger.com
Many thanks for Klara for the weekend, to Auntie Liz for hosting us on her property and to the cooks for feeding the hungry builders and keeping the fire going.