Materials
Cork in construction
With a negative ecological footprint, this thermal insulation is also breathable, fire-resistant, and comes with a lifetime guarantee.
CORK AND ITS CHARACTERISTICS
Cork is the name given to the bark of the cork oak (Quercus Suber). This tree, native to the western Mediterranean and the southwest of the Iberian Peninsula, can naturally regenerate its bark after it is harvested. When the tree is between 9 and 14 years old, this bark—of considerable thickness—can be harvested for the first time, yielding what we call cork. This process can be repeated after the same period of time it takes for the bark to regenerate.
Its full list of properties is unmatched by any other building material:
PROPERTIES OF CORK AS A BUILDING MATERIAL
Natural thermal insulation: A material’s insulating capacity is measured by its thermal conductivity, a property that depends on the material’s density.
The lower the material’s ability to conduct heat through its thickness, the better its insulating performance.
Cork’s thermal conductivity coefficient is around 0.037 to 0.040 W/mK—an extremely low value—due to the large amount of gas stored inside it (mainly hydrogen), which accounts for around 90% of its volume and gives it its characteristic lightness.
In addition, cork has a high specific heat capacity, meaning it does not heat up or cool down easily, and therefore maintains its insulating performance across a wide temperature range.
Acoustic insulation against airborne and impact noise: Cork’s internal structure, with its almost empty cells that give it high porosity and compressibility, makes it an excellent acoustic insulator.
Cork can absorb more than 60% of the sound waves that strike its surface, converting them into heat energy.
Waterproof: The hexagonal pores that make up its internal structure, together with the minimal water exchange capacity between cells, make cork a material that is virtually impermeable to liquids and gases and inaccessible to other compounds.
Due to its resistance to moisture, it is a suitable product for cladding spaces such as bathrooms and kitchens.
Breathable: Due to the gaseous content of its cells, cork allows air to flow slowly through its internal structure, enabling surfaces to breathe and acting as a climate regulator by stabilising air temperature and humidity and thus preventing condensation.
Does not rot: Cork’s resistance to rot is due to its tannin content and the absence of protein material susceptible to degradation. In addition, it is chemically inert, so when it comes into contact with liquids and gases it does not generate chemical reactions that could deteriorate it.
Not attacked by insects: Cork surfaces and structures do not create conditions for fungi or mould to settle. Suberin, the main natural polymer produced by the material’s cell walls, acts as a natural insecticide because it repels insects.
Lifetime guarantee: Cork is among the most durable organic materials. The lignin and polysaccharides in its cell wall—key polymers in the formation of the cellular structure of wood and bark—provide rigidity and make it highly resistant over time.
It shows virtually no ageing and does not lose its properties. These properties remain intact even in adverse environments such as seawater.
Reusable: As it is a material typically used for dry construction, it is very easy to recover and reuse in other projects, in line with the logic of the circular economy.
Recyclable: Recovering and reusing cork may involve recycling processes such as shredding to turn it into raw material for other products, such as sprayed or blown-in insulation, which is very common in refurbishments.
Biodegradable: Although it is a recyclable and reusable material, if it becomes waste, it is biodegradable due to its organic origin.
Renewable: It is a plant-based material that can be harvested without harming the tree and regenerates over the years, enabling a sustainable balance between agroforestry management and consumption.
Lightweight: This is a very low-density material due to its composition of tightly packed polyhedral cells at the surface with a hollow interior, 90% of which is air.
Resistant to pressure and compression: The high air content in its cells means it can be compressed to almost half its volume without losing flexibility; it is so elastic that it can recover its shape and volume once pressure is released.
Withstands high temperatures: Unlike other materials, cork retains its insulating properties across a wide temperature range thanks to its low thermal conductivity.
Non-flammable: Cork’s fire resistance stems from its natural role in protecting the cork oak trunk. When exposed to high temperatures, it forms a carbonised surface layer that protects the inner thickness of the material. In addition, it does not release toxic fumes when burned.
Maintenance-free: It is a highly insulating and waterproof material, so it does not become excessively cold and withstands the passage of time very well. Its maintenance is virtually nil.
Chemically inert. Cork is chemically inert. Its structure is not only impermeable to liquids and gases; when it comes into contact with them, no chemical reactions occur that could damage or destroy the material. This is why cork stoppers preserve neutrality of taste and smell and do not absorb odours.
Resistant to biological corrosion. Biological corrosion is the result of favourable moisture conditions and the onset of rot. Cork’s increased resistance to corrosion is due, among other factors, to its tannin content and the absence of protein material susceptible to degradation.
Its surfaces and structures are not a medium for mould formation, as they do not create the conditions for it to settle. Therefore, its resistance to fungi and mould is preserved over time.
Antistatic: It is a material that does not accumulate static electricity and is therefore resistant to dust and other harmful or polluting particles.
Healthy: Cork is a material free of toxic components and completely harmless to humans, both when inhaled and ingested.
Bark stripping, or “la saca”, is an ancient manual process by which this material is obtained. It requires careful, experienced hands to avoid damaging the bark or the tree. It is carried out by specialised professionals using a single tool: an axe.
This process has 5 phases [1]:
Opening, striking the cork vertically at the deepest fissure of the cork oak. The axe cut is then levered to separate the outer cork from the inner layer.
Separation, the bark is separated from the tree trunk by inserting the tip of the axe between the two and moving it to peel it off in panels.
Division, a horizontal cut is made between the usable cork sheet and the part that will remain on the tree.
Extraction, the sheets are carefully removed to avoid breakage, as the larger they are, the higher their commercial value.
Clearing, fragments are left at the base of the trunk and blows are struck on the cork oak wedges to drive away parasites.
Cork production uses five times less energy than that required to produce other insulation materials such as plastic derivatives, with the added value of being a 100% natural, reusable, and recyclable material. [2]
To thrive, the cork oak needs special conditions typical of the Mediterranean area: a mild climate with moderate average temperatures, no severe frosts, a minimum level of rainfall or controlled irrigation, and sandy soil tending towards clay.
In turn, cork oak forests have several effects on their surroundings: they conserve soil, recharge aquifers, control runoff, mitigate wildfires, and sequester CO2. This last action is significant because cork captures CO2 from the air for long periods of time, as it is a long-lasting material.
How does climate change affect cork oak forests?
The uncertainty about the sustainability of cork oak forests generated by climate change is driving research into the threats that harm them and the possible actions to respond to these changes.
The main threats that will affect cork oak forests, with effects already visible today, are reduced vitality and productivity caused by increased water stress, an increase in pests—especially Coraebus undatus—and a higher frequency of large wildfires.
A team from the Institute of Natural Resources and Agrobiology of Seville (IRNAS), in collaboration with the University of Michigan, studied over a 10-year period changes in the abundance and vitality of the cork oak (Quercus suber) in southern Spain, where the effects of climate change are most pronounced. Mortality rates of adult trees and recruitment rates were estimated and related to both climatic variables and soil type. [3]
In forests established on sandy soils, increased spring mortality is associated with a sharp rise in temperatures at that time of year, while increased winter precipitation was associated with higher survival. By contrast, in clay soils the effect is the opposite, linked to the adverse consequences of waterlogging and the greater aggressiveness of root pathogens. Consequently, climate change not only influences the survival of cork oak forests, but soil type also modulates the effects of climate on cork oak mortality.
Global warming projections will negatively affect cork oak forests by increasing adult mortality. Combined with the current lack of cork oak regeneration, this leaves a bleak future scenario for cork in the regions most affected by these changes. Without going any further, the cork oak in Extremadura is expected to be on the verge of extinction by 2040 due to rising temperatures caused by climate change.
Through sustainable forest management by organisations such as Life+Suber, climate change adaptation policies are being promoted that include biological, physical, and social actions to respond to the changes ahead. They argue that forest adaptation must address both resistance and resilience to the new adverse conditions.
Another tangible effect of climate change is the shift in the harvesting season. The cork campaign normally takes place during the summer months, but drought and increasingly early high temperatures are bringing recent campaigns forward to May. High temperatures are also expected to affect the quality of the final product.
Another important aspect is the air quality where cork oaks grow, as increased pollution may negatively influence cork production.
The forestry actions that cork producers are implementing to successfully adapt to change are diverse:
Improving stand vitality.
By applying silvicultural treatments to reduce density—such as thinning and selective cutting—with variations depending on other objectives such as fire prevention, erosion control, or hydrological regulation, the lifespan of cork oak forests can be extended.
Water is the main factor to consider in adaptation silviculture for Mediterranean forests in relation to increasing stand vitality. Therefore, it is necessary to increase water availability and water-use efficiency at the level of the individual tree by reducing competition to improve each individual’s vitality. With shrub cover protecting the soil from direct sunlight, evaporation losses are reduced and water availability is maintained.
Another technique to improve vitality is limiting the physiological stress of harvesting, which causes significant water and sap loss through transpiration from the stripped surface during periods of intense heat and low humidity. To this end, it is advisable to bring forward the start of the usual harvesting period to May and increase the minimum harvesting perimeter from 65 to 70 cm.
Adaptations in regeneration actions.
On the one hand, promoting natural sexual regeneration by extending regeneration periods and taking advantage of advanced regeneration, as well as reinforcing with sowing and thinning and maintaining natural selection processes. On the other hand, fostering the adaptation of reforestation: species, genotypes, soil preparation and planting techniques. As well as strengthening the restoration of degraded areas and areas affected by wildfires.
Reducing vulnerability to large wildfires.
This is achieved by modifying the fuel model at the stand scale through silvicultural treatments: thinning and selective cutting, selective clearing, pruning, and treatment of residues. In addition, work is carried out on designing fire-smart landscapes through the design of strategic areas, the use of prescribed burning, the creation of a forest cover matrix that hinders spread, and the promotion of heterogeneity at the landscape scale.
Promoting heterogeneity.
By promoting species heterogeneity, the existence of characteristic biodiversity linked to a given species is ensured. Actions include encouraging mixed stands, a diversified understory, and creating a mosaic of different structures.
Facilitating genetic adaptation.
With proper maintenance of genetic diversity and a reduction in fragmentation and low forest densities, adaptation of cork oak forests is facilitated.
Life+Suber programme
Climate change causes reduced vitality and productivity in cork oak forests due to water stress, increased pests, and a higher frequency of large wildfires, mainly due to reduced rainfall and rising temperatures.
The Life Suber project by the Quality Suber association aims to implement and transfer innovative forest management techniques in cork oak forests to promote adaptation to climate change and increase their resilience, thereby supporting their conservation and the continuity of the cork sector. [4]
Cork in Spain
The first documented cork industry in the world dates back to 1739 in Tossa de Mar (Catalonia), dedicated exclusively to the manufacture of cork stoppers. Since then, the cork industry has had its ups and downs, with strong international expansion in the 19th century and a concentration and specialisation in cork stoppers in the late 20th and early 21st centuries.
It was Catalan cork workers who, in need of cork, travelled to the regions of southwest Spain in the 1830s in search of cork from Extremadura and Andalusia. They spread across cork-producing districts, leasing cork oak estates and setting up the first factories in these regions. Catalan know-how and English capital were the driving force behind this industry in the southern lands. [5]
Globally, both Portugal’s cork industry—covering 25% of its forest area—and Catalonia’s—covering 3% of its forest area—have traditionally stood out.
Today, the main sources of cork in Spain, with 19% of its forest area dedicated to the sector, are also in Extremadura and, more recently, in Andalusia, where it is gaining increasing strength. The cork sectors in Extremadura and Andalusia have provided in recent years the raw material or semi-finished product to the Catalan and Portuguese industries for manufacturing. They now face the challenge of producing the finished product themselves.
In addition, it is in Extremadura and Portugal where more measures are being implemented, with controlled intensive cork oak plantations for better conservation and production. [6]
AMORIM
The Portuguese company Amorim, the world leader in cork production, has increased its product sales dramatically in recent years, rising by 64% in just one year compared to the previous year. Its production is divided into five sectors: cork stopper production, insulation, coverings, raw materials and agglomerates, and it has factories around the world and clients such as NASA and the European Space Agency. Particularly notable is the growth in sales of insulation and agglomerate production, which has increased to 18% this past year, as well as its presence in several locations in Spain: Amorim Cork España S.L. in Badajoz, Francisco Oller S.L. in Girona, and Victor & Amorim S.L. in La Rioja.
In addition, there are various professional associations and companies in this sector in Spain, including:
QUALITY SUBER
A producers’ group for the marketing and valorisation of Catalan cork, Girona. At Quality Suber, a large part of the profits from marketing has been allocated to research and R&D&I projects; among others, the Life+Suber project mentioned above stands out.
AECORK
Associació d’Empresaris Surers of Catalonia, founded in 1977 in Palafrugell, Girona, whose industry is mainly dedicated to wine-sector products.
BARNACORK
Specialists in the manufacture of cork components in Barcelona, attentive to advances in technology and design and committed to sustainability.
ASECOR
The Cork Cluster is the Innovative Business Group (AEI) launched by the Sanvicenteña Association of Cork Entrepreneurs, made up of companies in the cork sector, together with CICYTEX and the University of Extremadura.
CORCHO EXTREMADURA
Member companies with more than 100 years of experience in the manufacture and marketing of cork for construction in Mérida (Badajoz).
AZUCORK
Cork company specialising in construction in Badajoz.
Cork transport in Spain is mainly by road. Between the industries of the southwest of the Iberian Peninsula and Catalonia, there are companies dedicated to freight transport specialised in transporting this material.
A truck emits 3 kg of CO2 for every litre of fuel burned. On average, a truck consumes 30–40 litres per 100 km travelled. As there are 830 km by road between Extremadura and Catalonia, this means that the one-way trip of a single truck emits 1 tonne of CO2 into the atmosphere.
CORK IN CONSTRUCTION
Applications of cork in construction are mainly divided into two groups:
- Cork as insulation
- Cork in interior design projects
Compared to other eco-friendly insulation materials, it is important to bear in mind that cork offers better performance but also comes at a higher price—one that is more than offset by its insulating properties, durability, and minimal maintenance—while also contributing to sustainable and healthy production projects.
Cork can be used as a natural insulator in floors, walls, and roofs, with different systems that adapt to the specific needs of each project. This is thanks to its high insulating capacity with very little thickness compared to other eco-friendly insulation materials, its low thermal conductivity, and its high resistance to moisture. This eco-friendly material is renewable, rot-proof, and healthy.
We can purchase the material as a raw material or as a processed product. Buying unprocessed raw material can be either granulated or powdered, in 40 kg bags. Processed products come in the form of rolls, boards, and cork fabrics, made from cork granules cooked under pressure, and are typically used mainly as acoustic insulation under flooring. [7]
As for the different types of cork, we can distinguish them by how they are installed:
- Floors
- floors: insulation of slabs, flooring
- Vertical elements: internal face, external face, between walls
- Roofs: acoustic ceiling, insulation under the roof
And by the installation format:
- Sprayed
- Panelled
- Laminated
- Granulated
CORK BY INSTALLATION METHOD
CORK IN FLOORING
Cork in flooring can function as the finished floor itself or as insulation beneath the finish.
For this application in horizontal building elements, the system used can be of several types:
- Floating
- Glued under flooring
- Granular
In this case, cork acts both as a barrier to heat transfer and as an impact sound attenuator. It is a pressure-resistant, absorbent, resilient surface that requires minimal maintenance and offers advantages such as warmth and comfort, while allowing a choice of different textures, colours, and varied designs as a finish.
It is generally found in the form of tiles, which are divided into two types depending on their specific use:
