Hempcrete — the eco-friendly material breathing new life into Australian homes
Hempcrete is made by mixing hemp fibre, lime, and water which is then cured. Over the past three years, more than 100 eco-friendly homes have been built using it. Tasmania produces nearly two-thirds of the nation's commercial hemp
"The process of structurally making a building with hempcrete is not very far from a conventional building," Mr McMahon said.
"You need to give it a minimum of six weeks to cure — that's the primary cure.
"The overall curing process takes about 50 years to complete; the process is called carbonation as the material takes up atmospheric carbon, that's the lime, effectively returning to its mineral state, that's limestone."
In the past three years more than 100 eco-friendly homes in Australia have been built using hempcrete, with the use of the material particularly prevalent in Western Australia, New South Wales, and Victoria.
Hempcrete, made from mixing woody hemp fibre (from inside the hemp stalk), with lime and water, is then pushed into timber frames by hand to build an insulating wall.
Hempcrete's unique credentials attracted Sean Manners to the material for his new home at Westbury, in northern Tasmania.
He spent six years researching alternative building methods.
"It's a lightweight building product, so it's one building product to complete the whole wall," he said.
"Progressively over time, this house will take in more and more carbon.
"It will negate any carbon emissions we've had to make — for the concrete for instance; it'll be a carbon-negative house."
Mr Manners said the cost of the build per square metre was roughly equivalent to the cost of a double-brick house, "if you look at the cost over 10 years".
"[With] the savings in heating and health [and] the fact that you don't get any condensation [and] no mould, the cost would equal out," he said.
Building with hempcrete is fairly repetitive, labour-intensive work, so Mr Manners enlisted volunteers to help with tamping the mixture in place.
"Some have come for one day and I've never seen them again," he laughs.
"Then others, like Simon over there, come every day, so it's a wonderful thing."
New market for hemp industry
In building an eco-friendly home, you want to leave the smallest carbon footprint possible.
Shipping hempcrete across the country, or even from Europe, does not make much financial sense either.
A standard house uses a 6-metre shipping container's worth of hempcrete with the additional cost of shipping it from Sydney to Tasmania at approximately $6,000.
Tasmania produces nearly two thirds of the national commercial hemp crop, with the bulk of it grown for the food market.
President of the Hemp Association of Tasmania Tim Schmidt believes there is scope to sell it for building materials too.
"It's not terribly economic to be importing [hempcrete] from Europe, which has been happening," he said.
"There is an enormous opportunity here for the raw material that's being ploughed into the paddocks to be processed and sold locally for a much cheaper price."
Next year the association will look at the feasibility of setting up a local processing plant, with a Western Australian firm also eyeing off a new hemp decorticator.
In the meantime, Mr McMahon anticipates hempcrete homes on the Apple Isle will take off.
"I've got a number of people that are contacting me with fairly regular frequency," he said.
"I know of six projects that are set to proceed in the next 18 months, so it seems to be rapidly growing the demand."