Hempcrete is one of the oldest building materials on earth. When cannabis was deemed illegal, hemp was the baby thrown out with the bathwater. Its relationship with the psychoactive cannabis plant is known as marijuana led to the demise of a once-booming industry. Oddly enough, hemp is not psychoactive and contains 0.3% or less of the compound responsible for this effect – Tetrahydrocannabinol (THC).
Hempcrete is a biocomposite material created from hemp that can be used as an alternative to traditional building materials like concrete. It is made with hemp hurds (shives), limestone (or binder) and sand. It can be used for arenas, houses and much more. With the recent resurrection of the hemp industry, there are now more ways than ever to build with hemp.
Monolithic Cast Walls
Monolithic means “cast at the same time”. This is when slabs are poured in such a way that the whole unit functions as a single entity. It is one of the most common ways of building with hempcrete and bears resemblance to building concrete walls
First, structural framing is constructed with the conduits and pipes necessary for plumbing, electrical fittings etc. Then, wooden or plastic forms are used to identify the inner and outer wall surfaces. After that, the wall can be made from bottom to top, whereas the other side can be made in sections by pouring Hempcrete into the spaces within the formwork.
After the forms are placed, The Hempcrete is constituted on-site and poured into the spaces. The Hempcrete is poured to surround framings and fittings within the wall. It is crucial that all the voids are filled in the wall but anything that is missed could be patched after removal of forms.
Builders should tamp down Hempcrete situated at the surface to create high surface integrity. For better insulation, the interior Hempcrete should remain as loose as possible. Monolithic cast walls made from Hempcrete need about 24hrs to set prior to removal of forms.
Hempcrete itself needs quite some time to reach the peak of its strength; About a month to cure, up to even 3 months depending on environmental situations to dry out.
If you have a trained team of Hempcrete builders, the monolithic walls can go up quite quickly.
Hempcrete Bricks & Blocks
Hempcrete blocks are often made at the building site by mixing the materials needed and pouring into a mould. They can also be constructed by complex equipment that requires the use of skilled labourers. With the increasing demands placed on the rate of technological advancements, there are now entire factories producing Hempcrete bricks and blocks.
The production process goes as so:
The raw materials needed are mixed together in specified concentrations.
Hempcrete is then poured into a special press in blocks with widths of between 6 and 30 cm
The blocks of Hempcrete which are yet to solidify are then placed within an automatic conveyor belt. This moves them to an area where they could be stored while undergoing open-air drying. It takes about 6 – 10 weeks for the blocks to achieve their peak strength and hardness.
After the building frames have been constructed, the blocks are stacked or mortared together within it. The framing could also be abutted to create the wall assembly.
Complete Structural Wall Panels
Structurally insulated panels created in factories is another way in which hempcrete is used. These are basically custom wall sections which are formed by a combination of Hempcrete and structure.
It consists of individual panels which are assembled at the building site to create a building envelope on top of an already built foundation. There are many commercial structures built using this method.
This bears resemblance to pouring Hempcrete at the site. The distinction here is due to the use of industrial spray equipment. Instead of mixing the Hempcrete and pouring it into the formwork from the bottom up, it is mixed in large amounts using a cement mixer.
An industrial sprayer is used to fashion a wall with Hempcrete by using interior formwork. This method is great for roof ceilings and floor insulation too. However, this equipment is very expensive and requires a high technical skill set, plus it can be quite messy.
Hempcrete has been a key building material for the greater part of human history. There is so much potential for a healthier and sustainable building culture with Hempcrete. You can find some of our work with hempcrete at www.hemphomesaustralia.com!
We believe that Hempcrete is the building material of the future. Would you consider building with Hempcrete if it was a cost-effective alternative?