Ancient building materials: hemp and lime

Hemp-lime is a building material made up of two raw materials that have served 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 an NHL 5, which can also be mixed with Roman lime if necessary. Experienced do-it-yourself mixers who are keen to experiment also achieve good results with an NHL 3.5, to which they add a small amount of Roman lime.

To the lime binder

Process hemp-lime

In the oldest and most common construction method, the hemp-lime mixture is poured into a formwork, similar to concrete construction, and the mass is compacted. If you switch it off again after it has dried, a completely homogeneous wall has been created: with this process, of course, not only smooth walls, but all kinds of structural shapes can be poured. Such walls made of hemp-lime have a high insulation 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.

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Hempcrete blocks

The second construction method is bricking up prefabricated hemp-lime blocs, also known as hempcrete blocks. These building elements, similar to to bricks, are bricked up on the construction site with a light lime mortar. Choosing the right mortar is important as there is a risk of creating thermal bridges when using these blocks in conjunction with a heavy mortar. This risk does not exist when using light mortars.

To the masonry mortar

Hempcrete blocs are the ideal building material for interior insulation or to build a complete wall outside. The hemp-lime elements can be coated directly with a lime plaster on the outside and are then completely weatherproof.

To the hemp-lime

In the interior, you can then either plaster the walls with lime or clay. This is how you build very robust and durable walls.

A third way of processing hemp-lime is loosely spraying it on, similar to plaster, with a plastering machine. Since hemp-lime is a much coarser material than ordinary plaster, the machine technology must be robust and explicitly intended for this area of application.

Eco-balance of hemp-lime

Due to the combination of two ideal raw materials, hemp-lime has many structural advantages and also comes up with a very good ecological balance: hemp "saves" massive amounts of carbon dioxide, as the plant absorbs an enormous amount of CO2 in the course of its rapid growth. The hemp cultivation is completely free of pollutants (so-called 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.