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Hempcrete is a building material that is somewhat similar to concrete, though it differs in composition and use. The two main components of the mixture are lime and the innermost portion of cannabis stems. Other materials may be added, such as cement, sand, or other types of pozzolans, to increase the bonding strength of the mixture. Hempcrete is often poured or formed into blocks in a similar manner to concrete, though it tends to have a substantially lower compressive strength. One way that builders get around the lack of compressive strength is to use another material, such as wood, to provide adequate structural integrity.
Hemp is a term that is often used to describe cannabis plants that are grown for the industrial applications of their fibers and seeds. The useful fibers of these plants are found in the stems surrounding the woody core and covered by bark. This bast fiber is commonly used for rope, paper, and clothing. The woody core, often referred to as hemp hurds or shives, is the part that can be used for hempcrete. Hurds and shives are typically not suitable for the same variety of applications as the bast, though they have been a component of paper production and are most commonly used as an animal bedding material.
Concrete is often used as a structural element in building, especially when reinforced. Hempcrete is less likely to be used in such applications, due to the fact that its compressive strength is about 20 times less than that of concrete. Wood or other materials will typically be used to provide the structural elements of a building, while hempcrete is poured as a flooring or stacked in blocks as an insulating wall element. In addition to exhibiting insulating properties, hempcrete may also provide moisture regulation when used as a wall component.
One of the main benefits of hempcrete is that it is carbon negative, which can help to improve the sustainability or environmental soundness of a building project. Hemp sequesters a large amount of carbon dioxide (CO2) as it grows, through the same process of photosynthesis that is used by other plants. The amount of CO2 that is broken down in this way is typically larger than the carbon emissions involved in processing the final hemp and lime mixture. Some governments offer incentives for carbon neutral building design, so the use of hempcrete could be useful to those ends.