Hempcrete in a nutshell
Hemp concrete or hemp lime is a biocomposite material, a mixture of hemp shives and lime, sand or pozzolans. It is used as a building and insulation material. Hempcrete is easier to work with than traditional lime mixes and acts as an insulator and moisture regulator. It lacks the brittleness of concrete and therefore does not require expansion joints. The result is a lightweight insulation material that is ideal for most climates as it combines the functions of both insulation and thermal mass. It is a lightweight but solid and durable product.
France has been using hempcrete since the early 1990s. France continues to be an avid user of hempcrete, which is growing in popularity there every year. Canada has followed France’s lead in the green building technology sector, and hempcrete has become a significant innovation in Ontario and Quebec. It is used there to build unloaded insulating walls. Hempcrete does not have the required strength to build foundations. Hemp concrete is also used to renovate old stone or lime buildings.
There are two basic building techniques used with hempcrete:
– The first technique is to use molds to cast or spray concrete directly on site
– The second consists in laying prefabricated blocks. Such blocks are delivered to the project site, as in the case of standard masonry structures.
In both cases between the wood frame there occurs a drywall or plaster to enhance aesthetics and durability. Typical compressive strength is about 1 MPa, which is about 5% of the strength of residential grade concrete. It is a low-density material and resists movement cracking, making it suitable for use in earthquake-prone areas. Hempcrete walls must go together with a frame of another material that can withstand the vertical load in construction, as the density of hempcrete is 15% of that of traditional concrete.
Cautions when using hempcrete
The mixture contains a compound of plant origin, which shows increased caution in any contact with water and moisture. Hempcrete walls should have a gap between the wall and the ground to avoid capillary rise and water runoff at the base of the wall. Installation of the hemp concrete block can occur only above ground level.
Advantages of hempcrete
Hemp concrete walls are fireproof, moisture permeable, mold resistant and have excellent acoustic properties. Hempcrete provides high permeability due to the compound’s ability to easily absorb or release water vapor from the air. Increasing the density of the mixture allows the production of hemp materials for roof or floor insulation, while reducing the density allows the production of internal and external plasters. Like any crop, hemp absorbs CO2 from the atmosphere as it grows, so the hemp concrete block will store carbon dioxide after production and throughout the life of the block, providing positive environmental benefits. The specific amount of carbonates in the blocks increases with the age of the block. Thus, the main cause of the environmental footprint of hempcrete is the production of the binder and transportation.