What is Hempcrete and How is it Used?

Over the last century, the science of concrete and asphalt paving has seen numerous improvements. Many of these improvements help the environment, for example, asphalt is the most recycled material in the US. Other changes in concrete and paving are simply due to efficiency. Breathable concrete lets water filter through it and out, which prevents cracking and damage down the road. 

One of the more interesting developments in concrete in the last few decades has been a rise in hempcrete. Hemp is the cousin of the famously psychoactive marijuana plant. As drug legalization occurs throughout the US, the government’s stranglehold on the plant is lifting. This has led to a surge in hemp usage as well.

What is hemp?

Hemp is a fibrous leafy plant. Unlike marijuana, it has extremely low levels of THC. THC is the active ingredient in marijuana, and the primary drug synthesized from the plant. Like marijuana, hemp also grows as a weed, meaning that it doesn’t need pesticides or a costly watering regiment. The plant also grows thickly enough to block out other plants – and weeds – from growing nearby. 

Hemp has been used throughout the world for millennia for a variety of purposes. 

  • Hemp rope is strong, cheap, and easy to make.
  • Hemp makes canvas/clothing.
  • It can be made into paper.
  • Hemp can be grown as a natural buffer zone around crops to prevent invasive plants and insect attacks.
  • Hemp is used in the production of CBD, an oil that helps with pain and sleep. 

Hemp’s true value lies in its weed-like properties and it’s fibers. It grows quickly and with minimal management, thus, hemp crops can pop up faster than many other famed crops. It’s hurd, or stalk, is naturally strong and fibrous. The stalk is used in various ways that uses it’s fibers for strong, flexible material.

How is concrete made from hemp?

Hempcrete is a biocomposite. This means that it is made from both biological and non-biological materials. 

Essentially it is a mixture of three things: 1) hemp stalk 2) lime,sand, or pozzolana (a silica-aluminum mineral found in volcanic ash)  and 3) water. Combining the three into a type of slurry makes a versatile concrete-like substance. Hempcrete can also go by several other names. The lime,sand, or pozzolana makes the aggregate which is found in all concrete. The hemp itself is a binder, using it’s porous fibers and hardening water to keep the materials all together.

What are its benefits and drawbacks?

Benefits

Carbon-negative

Hemp is a fast growing plant that sucks up carbon dioxide. Using locally-grown hemp in hempcrete will keep the carbon footprint of your construction low. Of course, shipping it from other locations will hurt that footprint.

Light and easy to transport

Hempcrete is less dense than concrete, so it is much easier and cheaper to transport large quantities of the stuff. Additionally, the mix is not difficult to make, so a paving contractor could save money by bringing the hemp hurds (stalks) to a construction site and mixing it with the aggregate on-site.

Makes for good insulation

It is an air-tight and vapor permeable. This means that it can be used to keep buildings well-insulated and dry. It also is healthy, in that it’s natural properties mean no extra chemicals need to be added for its effect. Nothing is required as a coating for its insulating effects. Compared to asbestos or other insulation, it is a sturdy replacement.

It is great for filling in panels, and adding insulation to solid walls. Hempcrete is useful in renovating older homes and buildings to upgrade their thermal retention. 

Durable

Low-density means that hempcrete is resistant to cracking under movement. This is especially good for earthquake-prone locations.

Efficient

It takes very little hemp hurd mixed with binder to create a great deal of hempcrete. A whole field of hemp could possibly make enough total material to insulate an entire house. Traditional asphalt uses petroleum-based binder. Hemp stalk is also inexpensive.

Drawbacks

Hempcrete may be versatile and relatively low-cost. However, it does have some qualities that prevent it from being a replacement for traditional cement. 

It’s not very dense

The lack of density in hempcrete makes it a good insulation. However, it means that it can not be used as a structural material. Its density is only about 5% of regular concrete. Because hemp can not be used structurally, here is a list of things you can NOT do with it.

  • Hempcrete can not be used as a foundation. The foundation of your structure will need to be traditional concrete, as hempcrete will be unlikely to withstand the load.
  • It can only be used non-structurally. It must be set around timber, steel, or concrete. You can not build a house from hempcrete alone. 

Biodegradable

Hempcrete can biodegrade. This is great for avoiding pollution and waste, but not so good for parts of a building that need to interact with the environment. Hempcrete is bad as a foundation because it is not dense enough, and may begin to biodegrade after a time. If you have hempcrete on the exterior of your building, a weatherproof finish can be applied. Not so with foundations. You probably don’t want your building falling down because it’s foundation degraded.

Changing legality

As politicians play with laws, it effects our lives. Hemp may be a legal crop in 48 states now, but the right lobbyist from a big industry could change that. Over all, hemp seems to be on a general trend toward legality, but it is far from certain.

Considering hempcrete?

If you are thinking about getting some paving work done for your business, head to Reliable Paving. We will be happy to guide you. Our 35 years of experience and constant study of new developments in paving means we know all kinds of ways to minimize environmental footprint while paving on time, and on budget. If you want your paving done as well as possible, contact us today for a consultation.