Hempcrete is a composite building material, using a bio-fiber (the balsa wood-like core or ‘Shiv’ of a cannabis Sativa plant) and a mineral binder (Lime). Hemp, which possesses high silica content, when blended with lime, causes a chemical reaction causing the materials to produce a “bonded cellulose insulation”. 

Alternative Materials Hempcrete - Sheet1
Illustration showing process of making Hempcrete_httpsgreenbuildingcanada.ca2017advantages-building-hempcrete

The moistened binder creates adhesion between the hemp particles, and the final product contains a large number of voids, making it weigh only around 1/7th to 1/8th that of a concrete block.  The range of desirable thermal, structural and moisture-handling properties that Hempcrete possesses make it an excellent material for insulation, be it for roofs, walls, and slabs depending on the mixture of components.

A Thoroughbred Green Material

The ecological adaptiveness of Hempcrete by having a negative carbon footprint is cause for consideration to be a sustainable building material. This is a result of the carbonation during the curing process as lime turns into the limestone on top of the absorption of carbon dioxide by plants and plant products from the atmosphere. Its ability to regulate a building’s temperature and humidity by breathing, allows moisture to evaporate while reducing condensation and energy consumptions. 

This, in turn, has a greater effect in improving the thermal comfort for occupants. The composition of materials in hempcrete makes it impervious to molds and termites, is highly fire-resistant and toxin-free.

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Hempcrete construction blocks_Hempitecture

Hemp culture

Hemp is stereotyped for its potency of being psychoactive and is blinded by it, without seeing the other potentials of the plant as a building construction material. It has been grown and used as a building material in Europe for centuries now. The current developmental progress in using this building material has been its growth culture by certified commercial growers as industrial hemp. 

Its growth in popularity is hindered by the policies set by countries for the growth of Hemp considering its recreational uses and hence is not widely available in the market as a building material. Its properties of insulation and its comparable costs with other options in the market would surely make it more affordable as production volume increases.

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Hemp culture by licenced cultivators _FOODINSIGHT

Hemp is a crop mostly grown in rotation with other crops such as Barley or rye, without any need for pesticides, fungicides, or any fertilizers. It grows as a thick plant and does not allow weeds to grow along with it. Apart from its usage in building construction in the form of Hempcrete, hemp seeds are a nutritious food supplement rich in proteins, fiber, amino acids, and omega 3 oil. The outer fibers are blended with 45% cotton and used for clothing. 

The variant used for building construction and grown legally in Europe, Uk, and Canada is a close cousin of psychoactive marijuana with less than 5% THC content. This is periodically checked in farms to prevent other recreational uses of this plant and its products.

Construction coping Properties

Compared to concrete, Hempcrete has 95% lesser compressive strength coming in at 1MPa, limiting its usage to non-load-bearing uses such as in-fill walls complementing a framed structure rather than in foundations. The lighter weight of each block makes it easier to be carried around on a job site. In earthquake prone areas, Hempcrete’s property to be resistant to cracking due to its low density is put to use.

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Hempcrete as an insulating layer over brick_ISOHemp

Hempcrete blocks are used in the same dimensions as concrete blocks and are further used as infill walls along with a framed structure. It is used as an insulating layer between wall cavities by mixing in a mortar mixer for a couple of minutes and stuffed into wall cavities manually. The shuttering before applying hempcrete could be a temporary slip formwork with wood, steel, or plastic. 

The material is finished on the outside with a hard mix coating of 20mm thickness to protect it with a final-colored topcoat finish added. A resemblance to stucco finish can be noticed with Hempcrete and the insides can be finished with lime plaster or left natural.

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Hempcrete finished like stucco plaster_httpwww.americanlimetechnology.comwhat-is-hempcrete

The Variables

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Hempcrete as wall insulation with wooden formwork_Alex Sparrow

The materials and composition of these materials used for producing Hempcrete depend a lot on their quality, quantity, and characteristics. The woody-core of the hemp plant known as hemp hurd would consist of fibers that would vary in size, grading, volume, and length. A higher percentage of fibers would increase density by compensating for a loss in thermal performance. 

The different grades of lime that are used as a binder for hempcrete also could have varying characteristics to the final product. The additives used in lime and its composition may affect the setting time, strength, and durability of the hempcrete mixture. Even if hurd and lime variables are controlled, the absorption of water in the mixture by hemp hurd can cause the quality of Hempcrete to reduce. 

One of the most critical variables is the placement of hempcrete into the building. To make sure that the mix is well bonded and has integrity, in-wall and floor applications, manual tamping is required. Even more, the amount of tamping can affect the densities and can have a large impact on thermal performance.

References

editor and editor (n.d.). 6 Advantages of Building With Hempcrete. [online] Available at: https://greenbuildingcanada.ca/2017/advantages-building-hempcrete/.

Rise. (2019). Building with Hempcrete. [online] Available at: https://www.buildwithrise.com/stories/building-with-hempcrete.

Americanlimetechnology.com. (2012). What is Hempcrete? | American Lime Technology Website. [online] Available at: http://www.americanlimetechnology.com/what-is-hempcrete/.

Author

Darsan Babu, an architect, dreamer and a storyteller who loves to take on challenges and reform perspectives on some days, but sit by the mountain and quote words of Howard Roark on others. Would love to explore all things architecture, educate and shape the Urbanscape soon enough.

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