Hemp in Construction – The environmental way forward

Hemp-based Building Materials

The following article contains information on Hemp and its use as a Construction material……..

Hemp Concrete & Insulation

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Processing Hemp Stalks

Hemp bast or long fibre and hurds or inner short fibre can be processed and used with existing technology in construction. The hemp stalk can be incorporated into building materials straight from the field. Hemp fibre added to concrete increases tensile and compressive strengths, reduces shrinkage and cracking.

The demand for renewable raw materials is increasing. Currently many companies produce non-woven products like mats for insulation and car/vehicle composites based mainly on flax but increasingly now on hemp fibres. Hemp fibres have excellent potential – they can reinforce plastics, substitute mineral fibres, be recycled, can be grown ecologically, and have no waste disposal problems. A range of products can be derived from non-woven mats for a range of uses: insulation, filters, geotextile, growth media, reinforced plastics and composites.

Natural fibre composites (NFCs)are formulated from a blend of natural fibres such as kenaf, hemp, flax, jute and sisal, and thermoplastic polymers. NFCs are approximately 25 percent stronger than wood fibre reinforced thermoplastics and have none of the negative handling or environmental issues associated with glass fibre.

Hemp Concrete & Insulation

Hemp hurds are not only very absorbent, but are also uncommonly rich in silica. When mixed with lime, hemp hurds change from a vegetable product to a mineral. In this mineral state it is often referred to as hemp stone, and it weighs between 1/5 and 1/7 that of cement based concrete. Several hundred houses have been built in Europe using this material. Research is ongoing in the UK and Germany, where hemp hurds have been used for the construction of floors since the mid 1900s. Sometimes the hemp hurds are mixed with lime, water and either gypsum or river sand. When it is poured it hardens, and becomes mould and insect resistant. It can be used in drywall construction between formwork, as an interior and exterior insulation or be poured as a floor. The formwork can be removed within a couple of hours.

One advantage of hemp concrete is that it makes it unnecessary to have several layers of conventional building materials – it is outer and inner wall, and insulation all in one – it can replace bricks or cement-concrete, a vapour barrier, insulation, and plaster board or panelling. All that is needed as a finish is an exterior coat of whitewash to which pigments can be added if desired. The interior surface is an attractive cork-like texture that can be waxed or varnished (using a hemp based varnish).

One of the most popular hemp concrete products is Isochanvre, a French product. The manufacturers claim:

• excellent acoustic insulation
• breathes, prevents condensation
• self-draining and waterproof
• non-flammable (no toxic combustion products)
• resistant to rodents, termites, insects, fungi and bacteria (because of the silica content)
• easy to use, flexible and crack-resistant
• ideal for cyclone and earthquake prone areas due to its strength/weight ratio
• lightness
• able to use fewer finishing such as no plaster, painting or wallpaper.

With all this in mind, hemp can be viewed as an exceptional building material, whether we use ecological, architectural, practical or end-user criteria. Ecologically, using hemp hurds as concrete and insulation, makes sense. From a ‘life-cycle analysis’ perspective hemp construction materials win hands down. From its origins as an annual crop, hemp supports agriculture, it provides an alternative to timber/tree use and therefore tree clearing, does away with the need for mining, and requires no chemical processing in the defibration or stabilisation stages. Because of the simple, natural materials used, there is no air or water pollution, no waste is produced since all parts of the plant are used, and only minimal energy is required for processing. From the human perspective, it is easy and safe to work with since it is lime based, and it doesn’t require maintenance. The petrification process continues resulting in a stronger, better material with age. Like all hemp products, it is biodegradable.