Hempcrete is 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, lime binder, and water. A basic hempcrete recipe is 4-1-1. Four parts industrial hemp hurd, to one part lime based binder, to one part water. Changing the ratio of lime binder to hemp varies the strength and thermal properties of the hempcrete.
Hempcrete is very similar to concrete in the way that it dries, so you do have to work relatively quickly and efficiently once you’ve mixed up a batch, and if you’re working outdoors, then you’ll definitely want to check out the radar, and avoid rain or cooler weather for the best results.
To start, you’ll need to add the lime and water to a large bucket, and then combine them thoroughly using a mixing stick.
Now slowly add in the hemp hurd bit by bit, mixing the ingredients together the whole way through to avoid clumps. If the surface starts to look dry, stop and stir until the mixture is soft, wet, and consistent before continuing.
Once all of the ingredients are mixed together, it should result in a thick sludge-like consistency that is similar to regular cement. At this point, it is ready to be poured into a mold for bricks, a dugout hole to stabilize a fence pole, or in a cut-out pathway that needs filling. It’s best to wait until you’re ready to pour before mixing up a batch to keep it fresher, for longer.
Hempcrete will look like it’s starting to set almost right away, but that is just the moisture leaving the surface that is exposed to oxygen. Underneath, however, it will stay soft and goopy for quite a while, and it can take up to 48 hours to set completely under ideal circumstances. If it rains, or you add a bit too much water to the mixture, then it can take longer than that, so be careful and follow the instructions closely for the absolute best results.
There are many advantages 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.