Biomaterials in architecture

The construction sector accounts for around 40% of global greenhouse gas emissions: about 30% comes from buildings’ energy use, and the remaining 10% is attributed to so-called embodied carbon, which refers to emissions derived from the extraction and production of materials, as well as their installation on site.

While buildings’ energy efficiency has been regulated for years and is the subject of ongoing investment policies in renovation and public awareness, the same is not true for material-related emissions, which to date have largely been overlooked.

The latest revision of the EPBD, the Energy Performance of Buildings Directive in the European Union, approved in March 2023, includes for the first time the mandatory calculation of emissions in the construction of new buildings—an initial step towards regulating and limiting them, already in force in several EU countries. [1]

This new regulation represents a paradigm shift: high-impact, high-ecological-footprint materials that generate high CO₂ emissions and consume large amounts of fossil fuels during production—such as concrete, steel, or plastics—are now being required to present decarbonisation plans that in practice are unrealistic or rely on technologies yet to be developed, such as carbon capture. [2]

On the other hand, low-ecological-footprint materials that have been used in construction for thousands of years and had been sidelined due to the rise of industrialised materials—such as timber, earth blocks, fibre-based insulation, or lime-based products, among others—are once again gaining ground in the market, supported by investment in innovation, start-ups, and technologies that enable large-scale use.

These low- or zero-carbon-impact materials are typically natural, locally sourced, sustainable, in many cases renewable, and ensure minimal impact on people’s health and the environment.

Undoubtedly, the transition to a decarbonised sector requires recognising the value of, recovering, and developing these materials, which must become the new conventional construction to ensure a sustainable future.

1. TIMBER

Timber has become the leading construction biomaterial in recent times. If steel was the material of the 19th century and concrete that of the 20th, timber is expected to be considered the material of the 21st century.

According to the New EU Forest Strategy for 2030 carried out by the UNECE (United Nations Economic Commission for Europe), forests would absorb around 10% of the European Union’s CO₂ emissions. [3]

Trees therefore act as natural carbon dioxide sinks. Depending on the species, timber stores around 1.6 tonnes of carbon dioxide per m³, according to a study by FP Innovations in Canada. [4]

The UNECE highlights that using timber in the construction sector reduces CO₂ emissions by 40% when used as an alternative to concrete, and by 30% compared to steel. [5]

STRUCTURAL TIMBER

Due to its many benefits, the use of timber in construction has become increasingly popular in recent years. It is the benchmark biomaterial, extremely versatile: it can be used as a structural element capable of bearing significant loads and spanning large distances, or as cladding, enclosure, flooring, or furniture. [6]

CLT

The rise of prefabrication in architecture has positioned CLT—Cross Laminated Timber—as one of the leading options when designing buildings with sustainability criteria.

CLT is a construction system obtained by stacking 3, 5, or 7 layers made of sawn and glued timber boards, arranged perpendicular to one another.

The 90-degree layering of the timber boards gives the assembly bidirectional structural behaviour, capable of adapting to a wide variety of construction needs.

The CLT cross-laminated construction system is used in both vertical and horizontal elements, from load-bearing walls of up to 14 continuous metres, to internal partitions, as well as continuous intermediate floors and roofs.

The use of CLT as a construction biomaterial is considered one of the most popular and sustainable building alternatives on the market today. As a prefabricated and industrialised system, CLT helps simplify on-site processes, reducing construction time and cost, and becoming a highly competitive option against high-impact industrialised systems such as concrete or steel.

CLT MIX

CLT is available in different versions—one of them in the form of panels, also prefabricated, which ensure improved thermal and acoustic performance.

CLT panels with thermal-acoustic insulation are a recent variation of the original construction system, based on removing the central layers of sawn and glued timber and creating a void instead, like an internal box, into which thermal-acoustic infill is integrated.

This evolution improves mechanical performance—by reducing structural weight—while also enhancing thermal and acoustic performance—by integrating insulation inside—helping design in line with energy-efficiency and sustainability principles: less raw material for better performance.

In Spain, there is a CLT Mix manufacturer that uses timber from sustainably managed Pyrenean forests. Egoin is a company founded in the Basque Country, headquartered in Biscay, and operating throughout Spain. [7]

LIGHT TIMBER FRAMING

The light timber framing system consists of installing timber studs, spaced 40–60 cm apart, fixed together with cross members—horizontal timber pieces that act as horizontal connecting elements—forming structural lattices.

It is a prefabricated system, commonly used in North America since the 19th century, also known by its English name Balloon Frame, which uses timber as a construction biomaterial.

The voids created between studs are closed by integrating insulation materials, which are then covered with prefabricated timber panels. The result is a compact, self-supporting surface capable of resolving a home’s walls, floors, and roof.

One of the main advantages of light timber framing, beyond reducing construction time, is its energy efficiency: it is a construction system that acts as thermal insulation on its own. Not only is the overall weight reduced, but it also helps eliminate additional layers in the building envelope. This material saving has a positive environmental impact, generating a minimal ecological footprint. [9]

TIMBER FLOORING

There are different types of timber floors, including floating floors, synthetic parquet, and mixed parquet, a hybrid of the previous two. The choice of the final layer that covers the floor of our home once again highlights the dichotomy between natural and synthetic.

SOLID TIMBER PLANK FLOORING

Solid timber plank flooring includes both floating timber floors and glued parquet. The timber planks used in these surface-covering systems vary and adapt to the needs of each surface to be covered.

Natural timber parquet offers greater durability than synthetic options, as any damage the timber suffers over its service life can be restored through maintenance techniques such as sanding, thereby extending the biomaterial’s lifespan.

Due to its thickness and composition, natural timber finishes provide better insulating performance, as well as greater thermal inertia that brings warmth to the home’s interior. This reduces the need to heat the space with mechanical equipment, contributing to energy efficiency.

MIXED PARQUET

Mixed parquet is a natural-synthetic flooring. It consists of a lower layer of wood particleboard and an upper layer—considerably thinner than the lower one—of natural timber.

From an aesthetic standpoint, mixed parquet offers characteristics similar to solid timber flooring, giving the space a warmer feel than a synthetic finish.

The lower particleboard layer provides strength and durability. However, as it is not a solid natural element, mixed parquet does not allow maintenance techniques that extend its life cycle—it cannot be sanded because the top layer is too thin.

TIMBER JOINERY

Timber joinery is an alternative to the more commonly used PVC or aluminium joinery—timber is a natural and renewable material, while PVC is a plastic material derived from petroleum, and aluminium, despite its recycling potential with rates close to 100%, has a high ecological footprint. [11]

Timber’s insulating properties, both thermal and acoustic, improve the home’s airtightness and add warmth to the ambience.

The thermal transmittance of timber frames performs better against energy losses than PVC or aluminium, thereby supporting the home’s energy efficiency. As a thermal break is not required—as is the case with aluminium joinery—manufacturing is simplified.

Exposure of joinery to the exterior requires specific treatment and maintenance on one of its faces. Surfaces must be nourished annually with products that protect against direct sunlight and exterior dirt, such as stains or enamels, ensuring they are hygroscopic and VOC-free in their composition.

Due to their appearance and finish, hardness, and resistance over their service life, the most commonly used timber types for joinery, both exterior and interior, are pine, oak, larch, chestnut, and iroko. However, it should be noted that not all of these timbers can be supplied by local sawmills, so it is important to check the timber’s origin. [12]

2. TIMBER DERIVATIVES

Timber is a highly versatile biomaterial that has been used in architecture for centuries. Although its most common use is structural or in finishes such as cladding, furniture, or joinery, it still has additional applications in the construction sector.

WOOD FIBRE

Wood fibre as an insulating biomaterial is made up, as its name suggests, of small wood fibres obtained from wood waste, both of natural origin through the recovery of branches, leaves, bark, or sawdust, and from recycled wood of low commercial value.

The wood fibre production process, as with particleboards, begins by shredding the wood into small particles, which then undergo thermo-mechanical treatment that allows them to be separated into individual fibres. Additives are added to these fibres to improve fire resistance and protection against insects and fungi, such as boron salts.

Wood fibre can be supplied loose, in large quantities without a specific format—commonly used for blown-in insulation—but also in panels, rigid boards with more standardised sizes that facilitate application, or in rolls for smaller spaces or less conventional shapes.

Unlike other insulation materials with a higher ecological footprint and more widely used in building construction, such as polyethylene foam or expanded polystyrene, wood fibre has positioned itself as one of the most competitive timber-derived biomaterials on the market.

In sustainability terms, it is a renewable and biodegradable biomaterial with low environmental impact. It stands out for its thermal and acoustic insulation capacity, reducing heat and noise transfer, and also offers fire-retardant properties—fire resistance—and hygroscopic properties—the natural ability to regulate indoor humidity. [14]

CELLULOSE

Cellulose is an infrequently used option, but highly effective as an insulating biomaterial. It is an alternative to wood fibre insulation, and both materials share many similarities.

Cellulose is a plant-based material; plants are mainly composed of cellulose. It is the primary molecule present in plant cell walls, and is therefore found in large quantities in timber-derived biomaterials such as paper and cardboard.

The cellulose manufacturing process is based on reusing recycled paper, specifically newspaper. The material is shredded and mixed with water, forming a pulp of paper strips from which the ink—considered an impurity—is removed, and to which additives are added to improve fire-retardant, insecticidal, and fungicidal properties, such as boron salts.

This mixture undergoes a drying and pressing process and is then cut into small fibres, resulting in cellulose-based insulating biomaterial. As with wood fibres, it is a low-impact ecological process, promoting zero energy consumption.

Cellulose insulation is an economical and quick-to-apply system, and its applications include blown-in or sprayed insulation systems, as with wood fibre.

Its breathable and hygroscopic composition, in addition to regulating relative humidity and preventing the spread of mould, helps insulate buildings from sudden temperature changes, enhancing the feeling of thermal comfort inside the home. [15]

CORK

Spain ranks second worldwide in cork production, after Portugal, especially in the regions of Andalusia, Extremadura, and Catalonia.

Cork as a construction biomaterial is obtained from the bark of the cork oak, a tree mainly found in the Mediterranean. Cork extraction is an artisanal process carried out periodically, approximately every 10 years—the time required for the cork oak bark to regenerate—until the minimum thickness required for cork production is reached.

A circular incision is made in the tree’s bark using a specialised tool until the outer layer can be removed. This first layer is known as common cork; it is the outermost layer that regenerates most frequently, i.e., the most abundant raw material and the one most commonly used.

From the deeper layers closer to the cork oak trunk, virgin cork is extracted: a higher-quality type of black cork than common cork, used in cases requiring greater strength and durability. As it is closer to the trunk, virgin cork contains less air and more resin, which gives the material greater compactness.

With both biomaterials—common cork and virgin cork—after extraction the cork is dried. To eliminate moisture, the cork is left to air-dry for a few months, and then undergoes a boiling process to remove impurities.

Cork as a biomaterial has different installation formats, from sprayed cork—applied on site with a spray gun onto surfaces—to expanded cork in prefabricated insulating cork panels, to cork underlay in rolls of thin insulating agglomerated cork, as well as loose cork—allowing air cavities to be filled with blown-in insulation or poured directly on site. [16]

3. STONE

Stone is one of the quintessential biomaterials in the history of construction. As a biomaterial that comes from the earth, extracted directly from quarries, stone does not necessarily require a massive transformation process; rather, its own properties make it a self-sufficient option capable of meeting numerous needs on its own.

Although it is not a renewable material, stone is highly durable and therefore requires minimal replacement and has a long service life. In addition, it allows pieces to be recovered for new uses, following circular-economy principles. Waste generated by stone extraction and/or processing contains no toxic substances, making it possible to reuse the waste to manufacture engineered stone (such as porcelain flooring) or to recycle it, avoiding closing its life cycle.

ENGINEERED STONE

Natural stone, despite having properties that respect the environment and people’s health, is characterised by being a non-renewable biomaterial. This has created the need to find alternative construction solutions, integrating more synthesised anthropic processes while keeping stone as the raw material.

PORCELAIN STONEWARE

Porcelain stoneware is a type of engineered stone characterised by an appearance that seeks to imitate natural stone. It is a material composed of a portion of natural raw material mixed with synthetic additives.

The production of porcelain stoneware has a certain environmental impact. For its manufacture, agglomerated stone powder is used, typically with cement, which, after undergoing a high-temperature firing process, acquires properties of strength and hardness, as well as porosity.

The stone powder used in its production comes from the recovery of stone waste, both from natural stone offcuts from the quarries themselves and from the reuse of natural stone with a previous use. Therefore, porcelain stoneware avoids the direct extraction of natural stone from quarries, which has a positive impact given that it is a non-renewable raw material.

The final appearance of porcelain stoneware resembles that of natural stone, with an irregular, handcrafted look characteristic of stone finishes. It can be manufactured in large-format slabs for full façade or floor cladding, both interior and exterior, or in smaller formats for tiling and worktops.

TERRAZZO

Terrazzo is a construction material that comes from quarry waste, reusing unusable fragments of natural stone that still retain their physical properties.

Its manufacturing process begins by crushing stone pieces into small fragments, called aggregates, generally composed of marble chips, glass, granite, quartz, etc. These minerals are mixed with a binder, usually cement mortar, which, once set, forms the terrazzo pieces, giving them high hardness and strength.

The main application of terrazzo is in tile form for flooring, or in worktops. These pieces are manufactured by pouring the mixture into moulds, which then undergo a pressing, drying, and curing process.

Its final appearance will depend on the aggregate grain and thickness, as well as their composition, which in some cases may include pieces of glass, ceramic materials, or other recycled materials that give it a more decorative appearance.

As with porcelain stoneware, terrazzo is bound with cement, which means it has an environmental impact to consider, as cement is one of the highest-impact materials in the construction sector.

NATURAL STONE

Solid natural stone is one of the quintessential biomaterials, used in construction for centuries. It is a material with a low carbon footprint and no emission of toxic gases during its production process.

Due to its durability—a long service life with minimal maintenance required—and its resistance—to weathering, temperature changes, humidity, etc.—natural stone has become a basic biomaterial used in countless works throughout history.

However, there are two important considerations to take into account regarding the impact on the environment and people’s health of using natural stone.

The first is the ecological impact on the surroundings: it is necessary to consider the landscape and ecosystem impact of quarry stone extraction, as well as water use in extraction and cutting processes.

On the other hand, it is necessary to consider that stone is a porous material, so when using it for flooring it is necessary to incorporate a protective layer that may contain volatile toxins—VOCs—that are emitted into the air and end up being absorbed by our bodies. [18]

MARBLE

Marble is a metamorphic rock formed from limestone rocks subjected to high temperatures and pressures, reaching high degrees of crystallisation. Its composition is 90% calcium carbonate.

It is one of the most valued solid natural stones on the market for its aesthetic value, with a crystalline, veined, glossy, smooth finish.

It is a biomaterial resistant to high temperatures, supporting thermal comfort and household energy savings. Marble stands out for its durability: it has a long service life that requires little maintenance, and it is also reusable and recyclable. For this reason, its most common uses are worktops or wall cladding, mainly indoors.

GRANITE

Granite is an igneous rock composed of quartz and feldspar, formed by the slow cooling of magma produced when layers of the Earth’s crust melt, which gives it a granular, textured appearance.

Its extraction process and properties are similar to those of marble, whose most common finishes are polished and glossy. However, a sealing surface treatment is often applied to prevent the emission of possible radioactive gases, characteristic of the decomposition of this type of natural stone. While studies have determined that radioactive emissions from a marble floor or worktop are not dangerous, it should be noted that the sealing product used may emit small amounts of harmful toxins into the air. [19]

Even so, granite is positioned as the biomaterial most commonly used for worktops, but due to its high hardness, durability, and thermal inertia, it is also found in interior and exterior flooring.

SLATE

Slate, like marble, is a metamorphic rock composed mainly of quartz and minerals from the chlorite group. Its appearance is characterised by dark greyish tones, a rough texture, and irregular-finish pieces.

It is estimated that 90% of the natural slate used in construction is obtained in Spain, mainly from Galician deposits. [20]

Slate as a construction biomaterial stands out for its durable life cycle, as well as for its thermal properties and resistance to weathering and sudden temperature changes, making it a suitable option for roofs and exterior façade cladding.

LIMESTONE

Limestone is a sedimentary rock formed mainly of calcium carbonate, and it may also contain traces of minerals such as clay, quartz, etc.

Unlike marble, it tends to have more uniform textures. It is a biomaterial generally found in light tones, with a porous, matte finish, and a range of textures from smooth to rough.

Due to its versatility in properties and finishes, it is used for both interior wall cladding or flooring, generally with a smooth appearance, and exterior applications in its more textured form. As a porous biomaterial—due to its hygroscopic nature—its use in walls without waterproof protection helps regulate ambient humidity.

SANDSTONE

Sandstone is one of the most abundant natural stones in the Earth’s crust, making it one of the most sustainable options in terms of the depletion of non-renewable resources. It is a sedimentary rock composed of fragments of quartz, mica, and feldspars—minerals the size of sand grains.

It is a biomaterial with hardness, durability, and porosity that are ideal for resolving hygroscopic walls. Its fire resistance allows it to be used in fireplaces.

Because it is difficult to polish, sandstone has a grainy, irregular texture due to its composition rich in sand particles. As a result, it has a colour range in tones close to beige.

C RECYCLED AGGREGATE GRAVEL

RCD gravel—from the Spanish acronym Residuos de Construcción y Demolición (Construction and Demolition Waste)—is obtained from the crushing and sorting of waste generated during the construction or demolition of buildings, roads, etc.

It is a granular construction material generally used in concrete production, with numerous applications such as drainage, backing walls, foundation fill, land levelling, roof gravel, or even thermal-acoustic insulation.

The use of RCD gravel contributes to reducing waste in the construction sector, resulting in a positive environmental impact. Additionally, reusing aggregates extends their life cycle, representing a measure against the exploitation of non-renewable resources such as natural stone.

4. EARTH

Lime-compacted earth has been the material par excellence throughout the history of construction. However, industrialisation and the emergence of fossil fuels marked a before and after for the sector. With the appearance of new construction materials such as steel or concrete, earth took a back seat, coming to be considered an obsolete material, of solely historical and heritage value.

With today’s awareness of climate change and the desire to improve the environmental impact of the architecture sector on the planet, earth has undergone a revaluation, positioning itself as one of the most transgressive construction biomaterials of this century.

Building with earth, therefore, means looking back in time, learning from vernacular architecture, recovering the unique properties of traditional earth construction by adapting ancient techniques to new contemporary systems. [22]

Rammed Earth

In Spain, rammed earth construction has been a widely used system since Roman times, becoming popular and spreading across different historical periods up to the present day. However, it was not until the 1980s that interest in the technique began to revive.

Rammed earth, or tapia, consists of tamping earth in layers on site—the superposition of horizontal layers of a certain thickness, generally around 10 cm—within formwork so that, upon removal, solid load-bearing walls of compacted earth are obtained.

The base biomaterial for making rammed earth walls is earth, mixed with water and natural binders such as lime, with the option of adding straw or clay that provide cohesion to the whole.

Earth-based rammed earth walls follow the principles of bioclimatic architecture, harnessing the natural local resources of the environment to meet the home’s needs: insulating properties that promote thermal-acoustic comfort, wall breathability that improves indoor air quality, thermal mass that allows temperature to be stored over long periods and contributes to the home’s energy efficiency, low environmental impact thanks to a composition formed by minimally processed natural materials of local origin, etc.

On the other hand, it is a construction method that requires specialised labour, currently scarce, and a high on-site installation time. Mild climatic conditions are necessary—harsh climates, both extreme cold and heavy rainfall, deteriorate the material over time.

CSEB

CEB—from the Spanish acronym Bloque de Tierra Compactada (Compressed Earth Block)—is a construction system that uses earth as its main biomaterial, to which sand and clay are added, and may contain lime as a stabiliser.

It is an industrialised process by which the mixture is compacted under pressure by a hydraulic machine that forms the earth blocks. Structural strength is obtained after going through a drying phase in which excess moisture evaporates, leaving a compact block with high thermal mass.

CEB production requires considerably less energy than the manufacture of conventional bricks—around 1% of that energy—which represents significant energy savings for the construction sector.

Using the CEB system helps maintain relative humidity in the home at around 50%, which promotes the creation of healthy indoor environments. Additionally, the insulating properties of earth as a construction biomaterial promote the home’s thermal-acoustic comfort, and thus, its energy efficiency. [23]

5. PLANT FIBRES

Advances in bio-construction techniques have led to research into less common or conventional materials, but with performance results that in many cases meet the needs posed by architecture.

Today, there are construction biomaterials composed of plant fibres that challenge the construction sector to highlight the properties of natural raw materials, in this case, of plant origin.

Hemp

Hemp is one of the most effective plant-based biomaterials in the bio-construction sector.

It is a renewable biomaterial, with a reduced ecological footprint due to its rapid growth, and whose production involves low greenhouse gas emissions, in addition to the absorption of significant amounts of CO₂.

The main property for which hemp stands out as a construction biomaterial is its insulating capacity, a quality that contributes to the home’s energy efficiency. On the other hand, it is a biomaterial that, in addition to being protective against electromagnetic radiation, is hygroscopic, absorbing and releasing moisture depending on climatic conditions, and generating healthy indoor environments.

Hempcrete

The term “hempcrete” arises from the combination of “hemp” and “concrete,” understood as hemp concrete. It is a biomaterial, composed of hemp, lime and water, that presents itself as an ecological alternative with a strong future perspective in the bio-construction sector.

Hempcrete, despite being translated as concrete, does not possess sufficient structural properties to be self-supporting. It is used, in most cases, as a coating for vertical elements, but is also found in floor slabs or roofs.

Its application occurs in the form of prefabricated, non-structural blocks, forming bond patterns that make up the building envelope, or in mass form, being poured on site—this time similarly to standard concrete. Both require additional structural support to resolve the building’s loads.

Compared to Portland cement concrete, hemp presents a lightweight construction system, reducing the loads to be resisted by the building, in addition to the cost of its transport. [24]

Compressed hemp block

The compressed hemp block presents itself as an alternative to CEB (Compressed Earth Block).

These are solid structural pieces composed of hemp, hydraulic lime and mineral binders, such as clay, that provide the density and mechanical strength that differentiates it from mass hempcrete. The placement of the blocks is based on traditional masonry, in courses with staggered joints, adhered with mortar, forming self-supporting load-bearing walls.

The compactness of structural hemp blocks results in walls with high thermal mass, which store heat in summer and release it in winter, promoting the home’s interior thermal comfort.

Load-bearing walls built using this system do not require the installation of additional thermal-acoustic insulation layers. The insulating properties of hemp allow the block itself to be self-sufficient.

Hemp fibre panels

Hemp plant fibre panels as an insulating biomaterial act as a substitute for materials commonly used to insulate homes—polystyrene sheets, for example—non-natural materials that emit toxic particles into the indoor environment.

These are thin insulation sheets used to insulate facades, floors and roofs. They are available in the format of prefabricated pieces, as laminated hemp fibre distributed in rolls.

Cotton

Plant fibres also include cotton as a biomaterial in construction. The reuse of waste from the textile industry allows the biomaterial’s life cycle to be extended, promoting the circular economy.

Fabric remnants are recycled and defibred to produce semi-rigid panels—also available in bulk—that are placed in the air cavities of buildings.

Biodegradable, flexible and with low thermal conductivity, cotton is one of the most effective biomaterials for thermally and acoustically insulating a home. At the end of the production process of cotton as an insulating biomaterial, a treatment is applied that confers fire-retardant properties.

The use of cotton, being of recycled origin, represents an almost zero environmental impact, promoting the reduction of the carbon footprint. [25]

STRAW

The use of straw as a construction biomaterial dates back centuries in numerous parts of the world. It is a product of plant origin, biodegradable and renewable, obtained from the dry stalks of some cereals, such as wheat, barley, oats.

In our country, straw construction is not regulated by the regulatory framework, which results in the need for specific tests to be able to build with this material as a structural system or the use of another reinforcing biomaterial that complements the straw, in most cases wood. In other countries, however, there is regulation for building with straw bales as structural support. [26]

Prefabricated straw panel

Prefabricated straw panels act as load-bearing elements and enclosures that, due to their insulating characteristics and thermal mass, promote the home’s energy efficiency.

It is a prefabricated modular system composed of compressed straw panels—which provide the insulating properties—placed within a wooden structure—the load-bearing part. The straw bale is introduced by means of a press into the wooden box, at high pressure, so that the system’s strength increases, and in turn, the insulating capacity.

The prefabricated modules are stacked like bricks, creating a bond pattern in a simple and quick manner, giving rise to self-construction.

Its role as a load-bearing wall can only occur in small-scale constructions. For larger buildings, the straw panels act as enclosures, with it being advisable to introduce a structure of wooden columns that reinforces the whole.

PLANT-BASED PAINTS

The most popular interior paints on the market today are acrylic-based, made from petrochemicals derived from fossil fuels. However, with the rise of sustainable and healthy construction, natural-based paints have been gaining prominence in the market.

There is a wide range of possibilities among ecological paints, all of them with a composition free of chemical products that emit VOCs.

Natural paints are distinguished between plant-based paints and mineral paints.

Among the plant-based paints par excellence in bio-construction, the following stand out:

• Glue paint
• Casein paint
• Plant resin paint

On the other hand, mineral-based paints are:

• Lime paint
• Clay paint
• Silicate paint

We have recently published an article on ecological paints in our Research section.

6. CLAY

Clay is a biomaterial that has accompanied humanity throughout its history. Its use represents one of the oldest customs within the scope of our historical knowledge. It dates back more than 9,000 years, with the construction of civilisations such as ancient Mesopotamia, Palestine or Babylon.

Clay comes from the decomposition of sedimentary rocks—feldspathic—due to the action of air and the dissolution of water. It is found abundantly in nature, so it is considered an almost renewable raw material, whose extraction does not represent major damage to the environment and the depletion of its resources.

It is characterised by presenting plastic properties that allow clay to be easily moulded when moistened. Conversely, if the biomaterial is subjected to high temperatures, it solidifies and hardens, acquiring structural strength.

FIRED CLAY

Clay subjected to high temperatures—around 1,000°C—changes its properties and performance. Ceramics is the material resulting from the combination of clay, the raw construction biomaterial, water and fire.

The artisanal treatment that fired clay receives, avoiding artificialised chemical processes, allows the preservation of the biomaterial’s natural qualities. Properties such as thermal-acoustic insulation, low radioactivity, thermal mass, or hygroscopicity, among others, position treated clay as one of the most reliable options on the market.

CERAMIC BRICK

The production process of ceramic brick as a construction biomaterial begins with mixing clay with water. Subsequently, upon acquiring a mouldable consistency, it takes the shape of a prism through different possible techniques: manually with a prefabricated mould, extrusion or press.

The clay goes through a drying process to remove excess water, in the open air or in special drying ovens. After drying, the ceramic bricks undergo the firing phase in kilns at high temperatures around 1,000°C, which transforms the material chemically and physically, giving it properties of mechanical strength, durability, insulating capacity and fire resistance.

Ceramic brick is commonly found in the construction of facade enclosures or interior partitions. It is mainly used in non-structural vertical walls.

One of the advantages of ceramic brick is its firing at temperatures that allow fossil fuels to be dispensed with. That is, it is not necessary to use kilns fuelled with coal or oil to reach firing temperatures of between 800 and 1,000 degrees at which ceramic bricks are manufactured, which represents a much lower ecological impact than cement manufacturing, which does require high temperatures that necessitate the use of fossil fuels.

CERAMIC FINISHES

Although the most widespread use of clay-based materials is ceramic bricks, they are also commonly found as finishes, acting as the final visible surface layer that provides the warm appearance characteristic of ceramic biomaterials.

Their main applications are:

• Ceramic tiles. Traditional roof covering, generally sloped.
• Ceramic flooring. Ceramic tiling both indoors and outdoors

ADOBE

Adobe is a construction biomaterial, with clay as its raw material, that is gaining popularity in recent years. It is a traditional technique that, despite having been forgotten in Western countries, is still used today in developing countries.

Its manufacture is usually artisanal, composed mainly of clay and sand, in addition to straw or other natural fibres as a natural binder, which provide consistency to the whole.

It is a piece similar to brick, both in its production process and in its final appearance as a solid block in the shape of a prism.

NEW BIOMATERIALS

Currently, numerous studies are underway worldwide with the aim of discovering new ecological alternatives to already known biomaterials.

With current climate awareness, international directives pose the urgent need to expand the list of biomaterials, trying to steer the construction sector towards a model based on zero carbon footprint, zero impact and zero consumption. [28]

FERROCK

Ferrock presents itself as a biomaterial substitute for Portland cement. It is produced from steel industry waste of steel dust and silica, obtained from ground glass. Its composition comes from 95% recycled materials.

Steel dust, being a ferrous material, turns into oxide when it comes into contact with the CO₂ present in the atmosphere. In addition to the oxidation itself, the material’s reaction to carbon dioxide produces iron carbonate, which once solidified becomes Ferrock.

The hardening process of Ferrock is, therefore, the result of the combination of steel dust, silica, water and exposure to high concentrations of carbon dioxide.

The applications of ferrock as a construction biomaterial are, so far, all those that manage to replace cement. This includes its use in mass form, as a binding mortar, in paving or even compact blocks. It offers competitive properties in terms of its flexibility, good seismic behaviour and high compressive strength, greater than that of cement itself.

Ferrock is not only considered a biomaterial with a reduced carbon footprint, but presents itself as a carbon-negative solution. The capacity to absorb CO₂ during the drying process allows greenhouse gases to be captured from the atmosphere, which represents a strong contrast to the carbon emissions of Portland cement, commonly used in concrete, considered the third largest emitter of greenhouse gases worldwide.

MYCELIUM

Mycelium, known as “mycelium” in English, corresponds to the vegetative tissue of a fungus. It is the set of hyphae—multicellular filaments that make up the roots of fungi—that are buried underground.

Its growth mode resembles that of tree branches, in various directions and with complex structures. If it is grown in a closed space of controlled dimensions, as a mould, it ends up condensing, obtaining a hard and compact result, suitable for use as a construction biomaterial.

It is a fire-retardant material, resistant to mould and water, which can achieve a hardness greater than that of concrete. So far, its porous structure has proven to possess great insulating properties, with low thermal conductivity, like fibreglass or sheep’s wool or even polystyrene, in addition to interesting acoustic properties.

Depending on the treatment received by the fungal biomaterial, the chosen base substrate and the type of mould used, mycelium can resolve thermal-acoustic insulation systems, furniture, or non-structural finishes with the production of compact blocks.

The use of mycelium aims to replace plastic in building construction, positioning itself as a biodegradable and bio-contributory alternative due to its competitive performance. At the end of its useful life, the biomaterial is returned to the earth, contributing to zero environmental impact and the reduction of the carbon footprint.