Ancient 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 stones
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 interior insulation or for constructing a complete wall on the outside. The hemp-lime elements can be coated directly with lime plaster on the outside. The final coat is a high-quality silicate paint from Beeck to ensure that the facade is durable and well protected.
On the inside, you can then plaster the walls with either lime or clay. This creates very robust and durable walls.
A third way of working with hemp lime is to spray it on loosely, similar to plaster, using a plastering machine. As hemp lime is a much coarser material than ordinary plaster, the machine technology must be robust and explicitly designed for this area of 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.
Eco-balance of hemp-lime
Thanks to the combination of two ideal raw materials, hemp-lime has many advantages in terms of construction technology and also has a very good ecological balance:
Hemp 'saves' masses of carbon dioxide, as the plant absorbs an enormous amount of CO2 during its rapid growth. Hemp cultivation is completely free of harmful substances (i.e. pesticides).
As a building material, lime provides a lot of stability and has a positive effect on the room climate: thanks to its open-to-diffusion character, it is able to absorb moisture from the room air and release it again. 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, which in addition to the high alkalinity also helps protect against 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.