With the woody parts of the hemp stalk, after mechanical defibering, in a low-polluting process and little energy consumer is reached specific granules to be used as a construction material. Hemp granules have a very low density and with excellent thermal and acoustic properties. Due to their porous structure are used for the confection of mortars and insulating hemp concrete (IHC).

These granules must have specific properties, in relation to size, shape and characteristics, to be used in concrete. Those who do not meet the following criteria should not be used in hemp construction.

IHC is a dry mixture based on air and/or hydraulic binders, hemp granules and some additives that give it specific characteristics. Its insulating and acoustic properties allow it to be applied as insulation material on walls, roofs and floors.

In environmental terms hemp and lime allow a negative CO₂ balance allowing construction with “Zero Carbon”. Compared to conventional concrete, the amount of energy incorporated is 30 times lower and the balance in relation to carbon emissions is negative, about -190 kg.CO²eq/m³, 280 kg.CO²eq/m³ for conventional concrete.

In addition to the environmental advantage and multiple applications, IHC has a high vapor permeability (Hygroscopic), passive self-regulation of temperature and humidity, can be used in load applications with an integrated structure of wood, steel or reinforced concrete, presenting low density, fire resistance, comfort and amortization of indoor and outdoor noise.

The IHC with a dry density of about 300 kg/m³ has a compressive strength of more than 200 KPa and a thermal conductivity about 0.07 W/m.k As an example, a wall of 30 cm thickness has a thermal conductivity coefficient of about 0.22 W/m2K.

Thus, it meets the U reference values for climatic zones of Continental Portugal, with a more demanding value of 0.35 W/m2K for I3.

When poured from the mixer, it should not be a damp mass and should not have cohesion unless it cannot be squeezed or compacted. Water values equal to 1.6 weight of shavings + 0.6 weight of binder is a good start for mixers suitable for hemp concrete. For traditional mixers, the amount of water can be higher. By using a horizontal drum mixer, the mixing process is faster and more effective in achieving homogeneous mixtures.

The amount of binder depends on the type of use (roof, floor, walls) and the degree of pressing. Values of 140 to 200 kg/m3 of binder are common for roofs and walls, respectively. In the case of load-bearing floors, the amount of binder will be higher than 200 kg/m3.

For the durability of constructions with IHC, this product requires a knowledge of the raw materials and their properties, the ideal amount of water, conditions and curing times, type of support substructure, protections, etc.

Traditionally hemp concrete building elements are performed with support for reusable side formwork with the spacing of the wall thickness. Wall preparation and laying of hemp concrete should follow the applicable technical documents.

Insulating hemp concrete blocks (IHCB) are manufactured with raw material based on air and/or hydraulic binders, hemp granules and some additives that give it specific characteristics. It has thermal and acoustic insulating properties and therefore it can be applied as insulation material for walls, roofing and floors.

In addition to the environmental advantage and multiple applications, the IHCB have a high vapor permeability (Hygroscopic), passive self-regulation of temperature and humidity. These can be used in load applications with an integrated structure of wood, steel or reinforced concrete, which presents low density, fire resistance, comfort and amortization of indoor and outdoor noise.

The different block thicknesses make it possible to meet the various needs and challenges of regulation and thermal comfort, typically with thicknesses greater than 200 mm (see Products).

This is a simple masonry wall system with fine bed joints without the need for extra thermal and acoustic insulation.

The assembly of the IHCB building system is at all similar to the traditional construction of block masonry. Not adding extra difficulty in implementation, however, good practical rules should be taken into mind.

A wall executed in lightweight concrete blocks can receive any type of interior coatings, traditional or with projection, based on plaster or lime or both. In the case of exterior coatings, the requirements are higher and the mortar must meet more demanding mechanical requirements and good water behaviour.

Know that in Portugal ARE ALREADY PRODUCED IHCB that Natura Matéria collaborated for its development as part of our list of marketable products.

This constructive technique refers to the method of compacting, by successive layers, moistened soil in a formwork, and can be demoulding when the last layer is finished. In southern Portugal this technique was widely used in Alentejo.

Currently, compaction is carried out through a pneumatic hammer which provides faster execution than traditional rammed earth.

Rammed earth walls can be resistant or non-resistant if we choose to use a structure in another material, such as concrete or wood. In addition, these walls can be reinforced with bamboo or even steel, somewhat similar to reinforced concrete.

The earth has been the chosen material in bio-architecture or bio-construction, either by architects or by self-builders for its advantages in terms of healthiness and respect for the environment.

With the rammed earth it is also possible to take advantage of the colours and natural textures of earth, which provides very interesting aesthetic effects. This perhaps explains why architecture awards have been attributed to projects in rammed earth and it has been a technique used by renowned architects. The following projects are examples of this:

• Finalist projects of the 2016 Terra Awards.¹
• The Evora TARE Monitoring Centre, distinguished with one of the 40 buildings representing earthen architecture in Europe, under the “Outstanding Earthen Architecture in Europe 2011” award, by architect João Alberto Correia.²
• The Emergency Child Surgery Centre in Uganda by architect Renzo Piano. A reference architect in sustainable construction who has received several important awards, such as the Pritzker Prize (1998).³

Benefits ⁴

Earthen construction has the benefit of simultaneously providing control of temperature and humidity inside buildings, which maintains the presence of a salutary indoor air.

At the level of thermal behaviour, with its high thermal inertia it is possible to include solutions of passive solar architecture, accumulating heat inside during winter.

Regarding acoustic behaviour, in addition to sound insulation by mass, also the rough texture of the earth material allows the sound to disperse and is not directly reflected as on smooth surfaces causing echo in the compartment.

Absence of volatile organic compounds, known as COV, chemicals that evaporate and circulate in the air (such as the smell of paint or varnish).

Protection against artificial electromagnetic fields and permeance to natural ones.

Less radioactivity compared to some building materials.

¹ http://terra-award.org/finalists/

² https://www.apda.pt/pt/noticia/1154/etar-de-evora-ganha-premio-europeu-de-arquitectura/

³ https://www.archdaily.com/914606/renzo-piano-designs-emergency-hospital-in-uganda-with-rammed-earth-walls

⁴ Eires R. “Earth Construction: Improved performance with incorporation of biopolymers” (original in Portuguese), Doctoral Program in Civil Engineering, 2012. http://repositorium.sdum.uminho.pt/handle/1822/21010

CEB or Compressed Earth Block allows to build in a similar way to common brick masonry, but CEB is interlocked or interlocking and allows to settle the blocks with less use of mortar, being able to dispense their use in vertical joints. This type of construction allows a quick execution, ease of assembly and a reduction of construction waste.

In terms of building structure, this can be a conventional structure, in concrete or wood, or it can be incorporated into the perforated block itself. CEB, when manufactured with vertical holes, in addition to allowing the structure reinforcement, also allows the passage of pipes for hydraulic, gas, telecommunications and electricity networks, without opening of grooves, thus minimizing the production of waste during construction.

This constructive solution presents the benefits of earthen construction, such as:

• Control of temperature and humidity inside buildings, which keeps the presence of an indoor air salutary.
• At the level of thermal behaviour with its high thermal inertia it is possible to include solutions of passive solar architecture, accumulating heat inside during the winter.
• Regarding acoustic behaviour, in addition to sound insulation by mass, also the rough texture of the earth material allows the sound to disperse and not be directly reflected as on smooth surfaces causing echo in the compartment.
• No release of volatile organic compounds, known as COV, chemicals that evaporate and circulate in the air (such as the smell of paint or varnish).
• Protection against artificial electromagnetic fields and permeance to natural ones.

Adobe is a millenary construction technique and, like rammed earth, is one of the vernacular techniques of our country, predominantly in the central region.

There were essentially two types of adobe, with lime or straw.

Among the earthen construction techniques is the least used in the new construction today. However, it may have advantages in some situations, for example, compared to CEB it requires less industrialization and therefore also a lower cost and lower energy consumption. It is also lighter than CEB and can be used to make domes. But, it also has some limitations, such as being less regular and needing more mortar in the joints and plastering, besides needing structural reinforcement in seismic zones.

This constructive solution presents the benefits of earthen construction, such as:

• Control of temperature and humidity inside buildings, which keeps the presence of an indoor air salutary.
• At the level of thermal behaviour with its high thermal inertia it is possible to include solutions of passive solar architecture, accumulating heat inside during the winter.
• Regarding acoustic behaviour, in addition to sound insulation by mass, also the rough texture of the earth material allows the sound to disperse and not be directly reflected as on smooth surfaces causing echo in the compartment.
• No release of volatile organic compounds, known as COV, chemicals that evaporate and circulate in the air (such as the smell of paint or varnish).
• Protection against artificial electromagnetic fields and permeance to natural ones.