Traditional building materials: hemp and lime
Hemp-lime is a building material made up of two raw materials that serve people for centuries, not only in construction and in the manufacture of textiles. This mixture of lime and hemp shives, which are completely encased by the lime and firmly glued together, enables different construction methods.
The binding agent in the hemp-lime building materials is usually NHL 5. If the drying conditions are good, NHL 3.5 can also be used as an alternative..
Hemp-lime has a long tradition in France. The application guidelines and rules of technology are often tried and tested there and set out clear requirements for the hemp and the binder. The binder Batichanvre and the Isocanna from Saint-Astier fulfil these high requirements.
Isohemp hemp blocks
The second construction method is the laying of prefabricated hemp blocks. These building elements, similar to bricks, are laid on site using a thin-bed mortar. Choosing the right mortar is important, as the wall joint should be thin and stable when using these bricks. It should be thin so that it does not form a thermal bridge and it should be stable as it influences the load-bearing capacity of the entire wall. As an alternative to Isohemp thin-bed mortar, Conluto clay adhesive and reinforcing mortar can also be used.
Isohemp hemp blocks are the ideal building material for internal insulation or for constructing a complete external wall. On the outside, the hemp-lime elements can be finished directly with a lime plaster. Finally, a coat of high-quality silicate paint from Beeck is applied so that the façade is durably and well protected.
Indoors, you can then plaster the walls with either lime or clay. This gives you very robust and durable walls.
A third way of applying hemp-lime is loose spraying with a plastering machine, similar to plaster. As hemp-lime is a considerably coarser material than ordinary plaster, the machinery must be robust and expressly designed for this application. The binder Batichanvre is best suited for this.
Process hemp-lime
In the oldest and most common construction method, the hemp-lime mixture is filled into a formwork, similar to concrete construction, and the mass is compacted. Once the formwork has dried or is immediately removed, a completely homogeneous wall is created. Of course, this process can be used to produce not only smooth walls, but also all kinds of building forms. Such walls made of hemp-lime have a high insulating value and also good stability.
However, they cannot be used in a load-bearing manner, since load-bearing walls made of hemp-lime are not physically permissible. Since it is common to build the formwork around a wooden framework, the load is transferred via the wooden framework. The wall made of hemp-lime serves as an insulation level and at the same time as a plaster base level. Before constructing the formwork, it is possible to prefabricate the installation of pipes and lines so that they later disappear inside the hemp-lime. All the necessary installation lines are then already built into the insulation level. As a rule, hemp-lime walls are around 25 cm thick, but the wall thickness depends on the insulation value to be achieved.
The perfect finish: Kalamua – special plaster for hemp-lime
For the excellent building-physics properties of your hemp-lime wall (such as its high moisture regulation and vapour permeability) to take full effect, choosing the right plaster is crucial. With Saint-Astier Kalamua, we offer a modern single-coat plaster that is specifically tailored to the capillarity of bio-based wall build-ups.
What makes it special: thanks to the purity of the shell limestone used, Kalamua impresses with an elegant, warm natural white. This saves you time and material, as an additional coat of paint is often not needed at all – the wall remains as breathable as possible and retains its mineral aesthetic.
Life cycle assessment of hemp-lime
Thanks to the combination of two ideal raw materials, hemp-lime has many advantages:
Hemp is a fast-growing plant that absorbs CO2 as it grows. Hemp cultivation generally does not require pesticides.
As a building material, lime provides a lot of stability and can buffer fluctuations in indoor humidity: thanks to its open-to-diffusion character, it absorbs water vapour from the room air when humidity rises and releases it again when it falls. Another advantage of hemp-lime is the high alkalinity of the building material lime. Microorganisms, moss, mold or other fungal cultures do not like to settle on alkaline surfaces.The slight addition of hemp produces a high insulation value; together with the high alkalinity of the lime and the moisture-regulating properties, this reduces the risk of mold.
Hemp lime today
Hemp-lime is a building material that is currently experiencing a renaissance. It proves its ease of processing and its high degree of efficiency not only in the construction of highly insulating walls, but it has also proven itself in artistic and architectural areas: if the building material is in a doughy state, buildings or sculptures can be encased and poured completely freely. In the tiny house sector, walls and roofs made of hemp-lime are becoming increasingly popular not only because of the high insulation value combined with the low weight of the building material, but also because the insulation level, plaster base and wall can be made from a homogeneous material and in a single work step.