Hempcrete

Used for centuries, hemp* is one of the most sustainable organic building materials and one of nature’s strongest fibres.

[*The hemp used in construction is not the same kind of cannabis which gets all the publicity, but it is in the same plant family.]

Hempcrete is made from mulched hemp hurds (the woody inner parts of hemp stalks), water and a lime-based binder. It’s mixed together to form a slurry which is then put into formwork. It dries quickly and, over time, the chemical reactions between the water, lime and hemp will petrify and turn the lime back into stone. When dry, the outside surface is often rendered using a lime plaster. Hempcrete can also be retrofitted to replace the insulation with a hempcrete wall inside the external cladding.

Unlike concrete or masonry, hempcrete does not crack severely under movement. And because the hempcrete weighs about one seventh the weight of concrete it’s used as an insulator rather than a structural element and can be formed into bricks, panels or worked into walls. As an insulator it is highly efficient, it’s breathable and moisture resistant, and the air pockets in hempcrete absorb moisture when there’s high humidity and release it again when humidity decreases.

In regards to its green credentials, hemp takes approximately 14 weeks to grow so is highly sustainable. There is also no need for pesticides (it’s unpalatable to insects) or herbicides as it grows too quickly for weeds to effectively compete; this makes it an easy crop to grow organically. Hempcrete is also carbon negative which means that more carbon is taken out of the atmosphere by the growth of the hemp plant than is emitted from its production.

Hempcrete is gaining popularity in New Zealand as a natural, sustainable and organic product used for creating better environments to live and work in.