Building material of the month – Hempcrete

For years there’s been a growing movement around this fabulous, versatile and eminently sustainable material. As the first feature material highlighted on Natural Building Australia, we decided the buzz around this exciting building material deserved a special focus.

So, what is it and why should you think about building your home with a plant that used to be highly criminalised and often thought of as just a weed?

Hemp is grown for industrial purposes. In the last few years, hempcrete has become an increasingly popular building product. Created through combining water, hemp aggregate and a lime-based binder (mostly in a large horizontal mixer known as a hopper), hempcrete was first developed in France in the 1980s as a method of adding thermal performance to medieval timber frame buildings, whilst allowing the historic building fabric to continue working in the way it was intended tocreated. It continues to evolve and has become a highly prized and adaptable building product. The material is usually wet-mixed and cast on site in shuttering, around a structural frame (hempcrete is non-load bearing) but it can also be pre-cast into blocks or panels.

The insulation forms the entire wall with the load bearing timber frame fully encased. Hempcrete is not just an insulator – it buffers temperature and humidity, prevents damp and mould growth, making the building a comfortable healthy environment. The material is mixed in mortar mixers for 1-2 minutes and stuffed by hand or paddle into the wall cavities. The wall is slip-formed with temporary wooden or plastic “shuttering” forming the inner/outer surface forms. The material is lightweight and can be moved easily about the site in tubs and passed up bucket-brigade fashion to workers filling the cavities. Because it’s a natural material, site clean-up is easy because you can just till it into the soil. The material is finished on the outside with a hard render coating about 20mm thick to protect it with a final coloured or neutral topcoat finish. The result looks like any stucco finished building. The inside can be left natural or finished with lime plaster for a traditional natural building look.

Hempcrete has been around in Australia for around 20 years, with one of the first promoters Klara Marosszeky working tirelessly since 1999 to get the obscure product off the ground and distributed to owner builders across the country slowly discovering its amazing benefits. Klara has long promoted the ecological sustainability and durability of hemp, since there is no kiln baking in the production of the final product, hemp is the ultimate low embodied energy building material.

If you’re keen to get chatting to hemp practitioners head to our directory page and find someone near you who is working with this exciting new material.

Stay tuned for further blog posts devoted to all things hemp.