Did you know that hempcrete is one of the oldest building materials known to man?
It has been employed in the building of homes in a variety of different cultures around the world. Created by mixing hemp with lime-based binder and water, we can produce a very sustainable building material with relatively low environmental costs. And with the legalisation of hemp, the practice of building with hemp is experiencing a renaissance. However, it is still a largely untapped market.
Being a member of the Cannabis Sativa species, this plant woody-weed been misunderstood by many. While marijuana is majorly used for recreational and medicinal applications, hemp is grown for nutrition, textile, plastics, so many uses including building construction.
In the latest piece in our ‘How It’s Made’ series, we’re going to be looking at the construction of hemp homes.
Let’s start off with a remarkable benefit of growing hemp: it absorbs carbon dioxide from the atmosphere as it grows. It then converts it to biomass. Hemp is fast growing, – since at the end of the day, it is a weed. Hemp can be grown in various soil types, and handles different climates with surprising resilience. Furthermore, it grows densely; thereby conserving land.
Another natural resource that it conserves is water. It is eco-friendly because of its tolerance to pests, minimising the need for use of pesticides. It can also be organically grown due to its thick, bushy growth, which renders the use of fertilisers unnecessary.
A tractor-drawn harvester-spreader may be used to cut the stems and lay them in Windrows awaiting retting. There are three major retting methods: field or dew, chemical and water retting.
Field retting is the most popular method and is accomplished by placing harvested hemp on the ground for many weeks and leaving the process in the weather’s hands. The duration of this process varies but all rests on pectin degradation.
This system was applied during WWII but today there are more specialised harvesting equipment and techniques which have been applied in Europe.
Separate Hurd from Bast Fibers
Hemp stalks are made up of two main fibres, the bast fibres and the hurd fibres. The bast fibres are also known as long fibres and are found within the bark of stems. Meanwhile the hurd (or shiv) is known as ‘short fibre’ and is located within the wooden core of the stem.
The hurd usually makes up 70 to 80% of the stem and usually contains about 20 to 30% lignin. While the bast fibre is mostly used in textile production, the hurd comes in when creating hempcrete.
After retting, hemp fibres are dried and baled and taken to a central location for processing. In a process known as breaking, stalks are moved through fluted rollers to crush the hurds and put it aside from the bast fibres. A decorticator is a machine that can be used for this separation process.
Mix Hemp Wood Chips (Hemp Hurd) into Water and Lime
When the hurds have been collected, they are relieved of impurities, graded and de-dusted. Then lime is used in the mixture as a binder. Hemp hurds possess high silica content that permits cohesive binding with lime. Lime has many properties that make it ideal for the mixture such as:
- High porosity
- Low thermal conductivity
- Long-lasting binding of hemp hurds
- Easy to recycle and sturdy against cracks
Hempcrete mixing is largely dependent on the size of the building to be constructed. The mixting is performed using a large forced action pan mixer. A drum cement mixture can be used in the case of small quantities. A ratio of 4:1:1 can be used. That is 4 parts hemp hurds, 1 part lime and 1 part water. But you might want to confirm from your supplier.
- Put water in the mixer
- Add your lime
- Allow water and lime to mix into a slurry
- Introduce hemp hurds to the mixture and let them properly mix
- Once this occurs, stop the mixture.
To test your mixture, shape it into a ball then squeeze it. If the ball breaks into two then it is well-mixed.
Lay Wet Mixture and Allow to Dry
After getting your perfect mix, the next step is to allow it to set. This is usually done in the form of hempcrete walls. They are created through pressing, aging and packing of the wet mixture. Though light, they are solid, durable and have great insulatory properties. They are usually dried with open-air curing.
Isn’t it miraculous to see such a simple, formula that can build houses which could last up to hundreds of years? And better yet, they’re biodegradable. Hempcrete homes are not made from harsh chemicals that one day in the future, must return to the land that they were drawn from. Therefore, they will not leave pollutants. And even more-so, they’re healthier for humans. If you’d like to learn more about the benefits of hempcrete homes, check out our blog on 7 reasons to build your home with hempcrete!