Hempcrete is a mixture of hemp, lime and water that creates a thermally efficient and fireproof building material.
The hemp plant can be grown without the use of any fertilizers, pesticides, or fungicides. These fast growing
plants also put fiber back into the ground. The industrial hemp needed for this application only contains 9.2%
thc compared to cannibas that usually contains 15% thc. The plants are dried and seperated into two parts; the
fiberous part and shiv or woody core also known as rhetting. While the shiv is used to make hempcrete, the
fiberous material can be used to manufacture insulation, clothing, paper, and other everyday items. After the
shiv is isolated, it is mixed with lime and water to accurately achieve the appropriate consistency per application.
This mixture is the most common and can be utilized with various techniques. Three of which include; formed on site, modular prefabricated panels, and spray applied. For example, Hemp Technologies claims that their hempcrete product is stronger than concrete. The first US home permitted and built of hempcrete was built Ashville, NC. This particular example uses recycled plastic formwork that is lightweight and reusable. After the wood or metal studs are installed and the formwork is placed, the hempcrete is poured or shoveled into the formwork. It takes much less time to cure than concrete because it doesn’t slump due to the binding strength of lime. To finish the interior, the inside of the hempcrete walls are plastered with a clay, soil, and sand mixture. This assembly is rated R-40 per sixteen inches. Both of these materials are permeable and allow the building to breathe improving indoor air quality. When the humidity levels change outside, the wall takes humidity from the air and holds it until the humidity level lowers which they claim helps to regulate the relative humidity inside. Even though this system absorbs humidity from the air and is permeable, the hemp cellulose doesn’t rot because of the lime protecting it from moisture and its ability to dry out using fresh air naturally so that mold cannot form. When combined with lime, the hemp doesn’t decay, and therefore, never releases its carbon dioxide into the atmosphere. Additionally, the lime binder pulls carbon dioxide out of the air and gets harder over time as it becomes petrified. Using this method, a hemp home can sequester 20,000 tons of carbon. While the techniques of hemp based building materials are evolving and improving, the price of using hemp should begin to drop.