Originally known as Cannabis sativa, hemp is considered one of the oldest plants to populate the earth. Archaeologists have discovered traces of hemp fabrics from ancient Mesopotamia (now Iran and Iraq) that originated in 8,000 BC. And Chinese records show the consumption of hemp seeds and oils originating between 6 and 4 thousand BC. After its introduction in Europe, its primary application was geared toward the production of ship ropes and fabrics: even the sails and ropes of Christopher Columbus’ ships were culled from this material. Even the books released after Gutenberg’s invention of the printing press, and classic paintings by Rembrandt and Van Gogh consist of hemp.
Hemp is also a classic building material in the area of civil construction. Mortar consisting of hemp was found on the pillars of bridges constructed by the Merovingians in the 6th century, in the area now known as France. And the Romans utilised hemp fiber to reinforce structural mortar. Now, however, many nations impose legal barriers to prohibit the use of hemp as a building material. Yet hemp has been proven to exhibit thermoacoustic and sustainable qualities. The material can be formed into fibrous panels, coverings, sheets, and bricks.
Now, just a note: while hemp and marijuana do belong to the same species (Cannabis sativa), they stand as separate classifications with differing assets. Marijuana has higher percentages, up to 20%, of THC (tetrahydrocannabinol), which is the primary psychoactive substance in marijuana and is located primarily in the plant’s flower. Industrial hemp is produced for its seeds, fibers, and stem, and is comprised of approximately 0.3% THC, which is not sufficient to influence any individual.
Hemp needs little water to flourish and needs no artificial irrigation, and grows about 50 times faster than a tree. After being grown and cut, the plants are dried for several days before being grouped together and poured into aqua containers, that swell the stems. When dried, the fibers can be used for the manufacture of paper, fabrics, ropes, biodegradable packaging, biofuel, and building materials. And when it comes to building, the material can double as a thermoacoustic insulator, like glass wool or rock, or as hemp concrete, known as hempcrete. To make hempcrete, concrete mixers, hemp, powdered limestone, and water are blended into a thickened paste. Due to chemical reactions that take place amongst the components, the mixture stiffens into a light but resilient block. For the crafting of walls, the mixture can be lined up as building blocks, pulverized, or poured into the form of linear shapes, utilising the same practices as mud wall construction.
The genius of hemp concrete as a building material exists in its purpose as a multi-performance material. Hemp supplants mineral aggregates in traditional concretes, and it was blended into concretes and mortars to avoid plaster or clay brick retractions. When cured, hemp maintains a sizable quantity of air, with a density equal to 15% of classic concrete, rendering the material an ideal thermal and acoustic insulator. The material is a sound thermal insulator and boasts high thermal inertia. Hemp is light and porous, but hempcrete can maintain energy and release it at a gradual pace, rendering it suitable for climates with escalated temperature variation between day and night. The material offers sound fire resistance, is non-toxic, and resists mould and insects. Hempcrete is a carbon-negative material, and keeps added carbon in the material itself.
To accomplish these thermoacoustic properties, the material must “breathe” – interacting with the interior and exterior environment, permitting the hemp to absorb and disperse water vapor (humidity) and soften temperature fluctuations. Hempcrete walls can be receptive to coatings providing that they allow these exchanges.
The mechanical performance of hemp concrete is not as strong as conventional concrete or steel. It boasts a compressive strength of 2 MPa when it fails to go past a density of 1000 kg / m2, as compared to adobe bricks. Hemp is better applied on a fence than on self-supporting walls. Other disadvantages lie in the curing time, which can be eased with the use of bricks. And at the present time, hemp is a costly product with little info and person power available to work in conjunction with this technology.
Although this is slowly changing, progress is being stunted by the political war on cannabis and bans on source plants. Yet some countries have reversed bans on the growing of cannabis plants for medicinal and recreational applications. China grows more than 70% of the world’s cannabis total. Yet now, more and more countries are open to research, testing, and experimentation regarding hemp, with the aim of making this material more accessible for building.