Industrial hemp
INDUSTRIAL HEMP AS A BUILDING MATERIAL
Industrial hemp is a fast-growing crop that can reach a height of 4 meters in 4 months. A clear distinction should be made here between industrially grown hemp and hemp varieties grown for medicinal and recreational purposes. Hemp has been used as a building material for more than 1,000 years, and in the 1920s Henry Ford developed a car model made entirely with hemp and driving with hemp oil as fuel. Hemp can be grown in all countries in Europe and recently the laws have also been amended to make this possible.
Hemp is easy to grow and process. Hemp has a number of applications in the construction industry:
Hemp-crete
Hempcrete is a simple mixture of industrial hemp hurds (shivs), a lime-based binder and water.
Hemp hurd/shiv is the inner core of the plant’s stem. The hurd is chopped to lengths of around 6 – 25mm for use in hempcrete. It has a high silica content, enabling good binding properties with lime.
The mix ratio varies application to application, but generally in weight the ratio is 1.5/1.5/1.5 of hurd, binder and water respectively. The ratio will be determined by the final density required.
The dry components are thoroughly mixed together so lime is covering all of the hemp, and then the water is added.
Once prepared, the hempcrete mix is added to the formwork and tamped (packed down). The degree of tamping is also dictated by the density desired. While the formwork can be removed in a few hours, it can take up to a month for the hempcrete to fully dry; depending on wall thickness.
When it dries, it becomes a lightweight but strong building product that can be used in the construction of homes.
Hempcrete offers a number of benefits:
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It’s a great insulator
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Hempcrete breathes, helping to regulate moisture
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It becomes stronger over time
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During the curing process, it absorbs carbon dioxide
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It’s pest (including termite) and mold resistant
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Very low flammability, making it a safe material for homes
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An environmentally friendly product
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Safe to work with
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Fully recyclable
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Sound deadening qualities
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Less embodied energy in production
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Low allergenic
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As it’s hygroscopic, maintains a low humidity indoor environment
As mentioned, an advantage of hempcrete is its carbon sequestration attributes. Carbon is locked away in the hemp fiber itself, but hempcrete also continues to sequester carbon long after the building is constructed. This is due to a process whereby the lime-based binder absorbs carbon from the air over a period of time, petrifying the hemp shiv in the process.
One of the disadvantages of hempcrete is that it isn’t load-bearing so it must be used within a framework. The framework needs to be wood as the lime would react with metal. However, the hempcrete helps to protect the wood.
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Plastering/Rendering
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Hemp based plaster or render is essential the same as hempcrete, just applied more thinly. It adds a degree of added insulation and sound-deadening to existing walls. One of the advantages over conventional lime plasters is that it can be applied more thickly.
This is a product that can really stand the test of time. Hemp plaster has preserved caves in India that have been wide open to the elements for 1,500 years.
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​Hemp Foundations Are Strong And Elastic
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Hemp foundation homes and buildings are self-insulated, including thermal and sound insulation, resistant to rotting, rodents, insects, and they are fire proof, waterproof, weather resistant, and the walls breath so the rooms do not get stuffy. Hemp homes stay warm in the winter, and cool in the summer.
If hemp were legal in the UK or the United States, it would be the cheapest source of raw material for concrete-like foundations. Plus hemp hurds can be processed in existing wood mills without major changes to the equipment. Hemp-foundation homes are ecologically appropriate because they are inexpensive, and can be prepared on site using only a cement mixer, and the material would be cheap and abundant.
Foundation floors can be made in much the same way as the foundation. Hemp resists seepage, and so hemp cement is applicable for pouring onto a soil base to make a foundation floor. The floor insulation hardens into a solid mass which will not shift under pressure.
A German company produces a product called Mehabit, a hemp hurd substance covered with coal-based bitumen, which is sticky, and when leveled out on a hemp cement floor, will dry to form a thermally and phonetically insulated floor
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Hemp insulation
Insulation made from industrial hemp fibres comes in a variety of forms, including batts, rolls and solid panels.
The batts incorporate a small percentage of polypropylene or polyethylene to bind the hemp instead of chemical agents. Hemp batts have a similar R-value of other insulation products of the same thickness.
Hemp Insulation:
As in other building applications, hemp insulation doesn’t rot, helps to control moisture and is pest resistant – and is recyclable. Another advantage is in handling – the level of personal protective equipment used when laying down conventional batts is not required; although a mask is recommended to avoid inhaling dust.
When used as an insulation material, hemp offers high thermal resistance and has excellent sound absorption properties. It can also absorb a significant amount of moisture without any deterioration in its thermal performance.
© 2021 BY Gijsbert Hooft Graafland
