So what is Hempcrete? Quite simply, it’s a mixture of hemp hurds and lime. Hemp hurds are contained within the stems and stalks of the cannabis or hemp plant – they’re basically the central “core” of the stalk. When we process hemp stalks to remove the long, strong bast fibers, the hurds are what we are left with.
These hurds may not be suitable for weaving into fine textiles like the main “bast” fibers, but they are very useful nonetheless. They can be used to make animal bedding, paper, composite plastics, and much, much more. But it’s their usefulness in making construction materials that we are going to discuss in this article – particularly, the material known as Hempcrete.
To make Hempcrete, all that’s needed is some hemp hurds, a “binder” (usually a form of lime, such as natural hydraulic lime), and water. The ratio of hemp to lime and water may vary – some sources, such as the UK’s Endeavour Centre and the company Hemp Lime Construction, state that you need:
- 1 kilogram of chopped hemp hurd (also known as shiv)
- 1.5 kilogram of powdered binder (natural hydraulic lime or hydrated lime and metakaolin)
- Approximately 1.5 kilograms of water
This works out to be a ratio of 2-3-3 of hemp hurds, binder and water respectively. But over at Oregon Hemp Works, they use a different base ratio:
A basic hempcrete recipe is 4-1-1. Four parts industrial hemp hurd, to one part lime based binder, to one part water.
So why this difference in ratio? Well, the company UK Hempcrete has this to say:
Changing the ratio of lime binder to hemp varies the strength and thermal properties of the hempcrete
So it’s a good idea to work with a professional specialized in building with Hempcrete, if you want to keep this kind of decision out of your hands. However, if you do decide to mix your Hempcrete yourself, you may to experiment with various different ratios before making your final decision.
One company, Tradical, is renowned within the industry for producing some of the most effective lime binders for use with hemp hurds. They have a factsheet available specifying different ratios of hemp to binder and water, which have been developed for various different applications including wall construction, floor screeding, renders, plasters and insulation.
So How Is Hempcrete Used in Building?
The most common method of using Hempcrete in building is by “casting” it onto a wooden or metal frame. With this method, it is necessary to first construct the frame; next, handheld tools are used to plaster the Hempcrete onto the frame. Once the Hempcrete has been cast on to a section of the frame, it is then necessary to use structural supports to hold the Hempcrete in place until it fully dries (usually around 4-6 weeks). Then, a final layer of plastering, paneling or stucco can be laid as desired.
A second method for building with Hempcrete involves the use of a specialized machine that sprays the mixture onto a timber or metal frame. Again, this method requires the use of a constructed frame, but as it requires much less time and manpower than the traditional casting method, it may work out considerably cheaper. On the other hand, the equipment (and knowhow required to operate it!) is not available everywhere, and is expensive to hire where it is available. Currently, if you’re in the USA you may be out of luck finding such a service – but if you’re in Europe, it’s highly recommended to reach out to Laurent Goudet, president of AKTA, a French company that rents out the equipment and workers by the day.
As well as these two methods, it is possible to utilize one or two other possibilities. One possibility is sourcing ready-made Hempcrete bricks from a company such as the Canadian firm Just Bio Fiber. This company makes a range of prefabricated blocks that look almost exactly like Lego bricks and stack up in an identical manner – and according to the company, they can be stacked up to 800 ft (243 m) tall with no problem. The huge advantage of this system is that once the bricks are fitted together, the wall is pretty much built! No need to wait weeks for the Hempcrete to dry, as with the casting and spraying methods. For Europe, it’s advised to check out UK Hempcrete’s range of prefabricated hemp products.
Yet another possibility is purchasing prefabricated wall panels made from Hempcrete, which can be simply and neatly fixed together to construct your new home in a fraction of the time it takes to cast or spray tons of Hempcrete onto a frame. These prefabricated panels are now available from several different manufacturers – in Europe, UK Hempcrete should be able to meet your requirements for prefab wall panels; in the USA, American Lime Technology produces a range of pre-cast wall systems; in Asia, Singapore-based firm Studio Green offers prefab panels of various types.
What Are the Benefits of Building with Hempcrete?
There are many concrete advantages (pun slightly intended!) of building with Hempcrete. It is tough, strong, durable, and lightweight, and compares well to conventional building materials by most measures. It is exceptionally good at regulating temperature and humidity, to the point that supplementary forms of insulation may be entirely unnecessary. It is also remarkably fire-resistant, and on top of that, it’s practically impervious to the effects of damp and insects, unlike many forms of wood used in construction!
The downsides to building with Hempcrete are few and far between. It’s not always widely available, first of all. You’ll still have to use regular concrete or another conventional means to lay your foundations, as Hempcrete does not meet the requirements. Furthermore, building with Hempcrete will generally end up costing the average future occupant as much as building with conventional materials. Right now, it doesn’t represent the ultra-cheap option that many fans of sustainable living wish to implement – but this is largely to do with limited availability of materials, and costs will almost certainly drop as the technology becomes more widespread.