Cork: Fact File

Abbie Harby
"If we were meant to stay in one place we'd have roots instead of feet" and so I move - in cities, between cities, up mountains (and back down again!). And all that using my feet as much as possible - the first mode of transport known to man and the cheapest! I love the outdoors and being in green space. I'm passionate about trying to protect and improve all that we've got and all that we could have to give every single part of nature the best life possible.

Although currently not one of the most widely used bio-based materials, cork is still a viable option in construction, with countless benefits making it well worth considering. As more and more bottle stoppers are being made of plastic corks or screw tops, the sustainable cork industry could do with a boost. So, perhaps you could help by utilising this natural material in your building project. Take a look through our cork fact file to find out more.

Sixty percent of cork oak production takes place in Portugal, although other regions of southern Europe and northern Africa also have a booming industry. Cork oak is such a vital component of the Mediterranean economy that they have made it a protected species.

Cork could be one of the most sustainable natural materials out there as it is the only tree that can have its bark removed without killing it. This means, after the first 20 years of growth, it can be harvested every nine years over its 250-350 year lifespan, with a yield of a couple of hundred kilograms of bark each time. The regular removal of the bark even improves the quality of the cork, making it smoother!

The sustainability factor doesn’t stop there: it is also socially and ecologically sustainable. All harvesting is done by hand; the axes used are made locally. The skills are passed down through the generations, creating thousands of jobs for years on end. A well-maintained cork forest is home to an array of wildlife, from medicinal herbs to bees and Lynx. Not only is this an environmental coup, but also generates “over 1300 €/ha/year for the ecosystems services associated with a well-run cork oak forest”.

Types of Cork in Construction

Cork construction products are made from one of the two types of agglomerates which are produced in different ways and therefore have different functions:

Pure expanded agglomerate

Also known as ‘black agglomerate’, the raw material of this can be falca cork, virgin (the first cork harvested from a tree), or reproduction cork. Granules of falca are expanded by heating water to 350-370°C and exposing the granules to steam. This leaves a block of expanded cork which can be cut into plates of various thicknesses.

Expanded agglomerated cork is ideal for providing vibration, thermal, and sound insulation. Whereas natural cork has closed cells, meaning the absorption of sound is weak, expanded agglomerated cork has open pores between the granules, helping to absorb acoustic and vibration energy.

Compound agglomerate

‘White agglomerate’ is the primary raw material here. By crushing the waste product from making cork bottle stoppers, granules are obtained, which are then joined together using pressure, temperature, and resins. This can be made into sheets, blocks, or cylinders.

The resin, either artificial or plant-based, allows compound cork agglomerate to have a huge variety of uses, including: insulant in the electrical industry; flooring; wall and roof coverings; sound and thermal insulators; furniture, rigid panels, and parts for dividers.

Cork with rubber is one example of a compound agglomerate. The individual characteristics of cork and rubber combined make a flexible, elastic, but solid material. The resilience of rubber is blended with cork’s “mechanical resistance and dimensional stability”.

Uses of Cork in Construction

Walls and Facades

Wall finishes can be found as plain or patterned tiles, cork bricks, or blocks. These blocks, for instance, are made from compression-moulded cork which comes in a variety of shapes arranged in a repeating pattern. Cork has many other functions for walls, too:

  • Bricksor blocks are just one way of constructing with this sustainable superhero. This video shows how it can be used for display walls, stairs, office cubicles, and mezzanines.
  • As cork is packed with air pockets, it functions well as sound insulating wall coverings.
  • Interior decorative coverings and exterior finishes.
  • Thermal insulation for double walls.
  • Façade insulation using External Thermal Insulation Composite Systems (ETICS) which has multiple benefits: reducing condensation; increasing usable space due to being thinner but with the same heat transfer value; better waterproofing.
  • Pure expanded agglomerate in wall insulation.
  • Interior wall covering using sheets of cork agglomerate improves thermal and sound insulation. It comes in a variety of aesthetics, either in its natural state or layered with varnish, wax, or oil surface treatments.

Flooring

Typically, ground and compressed cork board is used as insulating sub-flooring. It also often comes as tiles or planks. More contemporary ideas for cork flooring have seen the corks used in wine bottles being recycled and laid vertically side by side with their tops at one height. The final product looks mosaic-like. What else does it offer?

  • Floating or glue-down flooring options are both available as completely natural products or with varnish, wax, or oil finishes.
    • Floating flooring has several layers: an agglomerate cork layer, an intermediate layer of high-density wood fibres, and a lower layer of agglomerated cork. This is named ‘floating’ as it is directly and easily applied to existing flooring without being glued.
    • Glue-down cork floors comprise of a single sheet of high-density agglomerated cork, or a decorative sheet of high density agglomerated cork. The subfloor must be waterproofed and levelled when the glue-down flooring is applied. Usually, the tiles have a surface treatment making them more resistant.
  • Floor underlays.
  • Decorative flooring.
  • Cork gives the floor a little spring, meaning it doesn’t impact your feet, legs, and back the way concrete or tile floors do.
  • It is also noise-absorbent. This could be ideal for constructing spaces for those sensitive to, or creators of, noise such as children, the elderly, and the frail.
  • Pavements can be made from cork thanks to its durability and the fact that it is scratch proof. The same applies to floor and wall tiles for the interior of buildings.

Roofs and Ceilings

  • Cork granules are used to make agglomerate, which is used for ceilings and roofs as well as walls.
  • Insulation cork board can be used for terrace coverings where it acts as a thermal insulator, as well as being an extra water-proofing element.
  • For the insulation of flat and metallic roofs, a pure expanded agglomerate is an ideal option. It can withstand permanent pressure without being damaged.

Interiors

  • Interiors made from cork benefit from the fact that cork as a material is naturally anti-microbial, so ideal for countertops in kitchens and bathrooms. It is resistant to mould and fungus because, although breathable, it is water-resistant; no moisture or fluid can pass through.

Other uses in construction:

  • Cork granules can be used in concrete structures for expansion and compression joints, meaning cork can also be used in building tunnels, dams, and other concrete structures.
  • Cork dust can be used as biomass to generate energy with neutral levels of CO2. This can offset some of the emissions and embodied carbon of the construction industry. It is also used in wind turbines.

Cork Around the World

Similar to hemp, there may be environmental issues associated with cork in terms of availability and transportation. Cork requires a lot of sun and sandy soil, but little water. Hence, the seven primary cork-growing/producing countries are: Portugal, Algeria, Spain, Morocco, France, Italy, and Tunisia.

United Kingdom

While examples of cork construction in the UK are few and far between, one couple in south London has proven that it is possible. Their 13cm thick cork cladding is fixed to breeze blocks on the inside and outside of an extension to the Victorian terrace house. Although this means that the house is bigger, thanks to the cork it is better insulated and easier to heat – vital in the British climate!

In Scotland, the walls of Hazelwood School in Glasgow were decked out in cork to give the hearing- and sight-impaired children a safe, soft, tactile experience and means to navigate.

Saudi Arabia

Looking half-finished, the Gharfa pavilion in Riyadh is partially filled with bottle corks. As much for aesthetics as it is for any kind of insulation, it reflects the ruinous state of some local ancient structures, thereby being both modern and alluding to tradition simultaneously.

United States

When the philosophy department of New York University, dating back to 1890, was renovated, the entire ground floor was replaced with cork. In addition to the usual health, comfort, and aesthetic benefits this provides, it was malleable enough to fit with the curvilinear wooden auditorium.

Advantages

  • Quick to install.
  • Cork is relatively affordable, though transport costs may vary due to availability in your location. It won’t need any cladding externally nor plastering internally and requires little processing, so is cheap to produce.
  • For thousands of years, cork has been used for fishing equipment since it is so lightweight and can float on water. This translates well to the construction industry.
  • Naturally fire-resistant.
  • Its flexibility makes cork less likely to break. It can return to its original shape even after being compressed and can be fitted perfectly against walls. This is possible because of the air/gas pockets in cork, which reduce in volume when compressed and regains shape and volume once the pressure is released.
  • Cork is an insulator ‘triple threat’. Not only does it possess low heat conductivity, but also of sound and vibration due to the gas pockets. This characteristic means cork has one of the best insulative qualities of all-natural materials.
  • It has one of the lowest heat conductivity rates of common materials. Air pockets in the substance ensure reliable temperature regulation.
  • Cork is breathable.
  • Mould-resistant, cork is ideal for damp climates. While these conditions tend to attract insects, cork has a natural scent that deters them.
  • It has a nice smell as well as an aesthetically pleasing pattern.
  • Cork is naturally non-toxic, releasing no volatile organic compounds (biological chemicals that are released as gases emitting odours and pollutants).
  • This could be the ideal natural material for allergy and asthma sufferers as it does not absorb dust.
  • The material can last for decades, is easy to replace, recyclable, and biodegradable.
  • Cork is sustainable, being renewable, recyclable, and reusable.
  • The honeycomb structural make-up means that cork can cope with high levels of friction and is extremely resistant to wear.
  • Its impermeability (water resistance) means cork doesn’t rot. Being waterproof is not only a prerequisite of a good building material but it also means the end product will last longer.
  • Manufacturing of cork generates almost zero waste.
  • Cork is aesthetically pleasing: interiors using cork often feel warm, welcoming, natural, and homely. Moreover, even if you and your neighbour were to use cork in the same way, both spaces would look unique: every piece of bark is different in terms of its texture, grain, and colour. Your space will be one-of-a-kind!
  • Cork requires minimal maintenance.
  • Agglomerated cork walls achieve the same efficiency as brick walls at less than half the thickness and one-twentieth of the weight.

Disadvantages

  • The softness could be a curse – flooring particularly can be damaged quite easily by sharp items. Use carpet protectors to spread the weight and minimise the damage.
  • Despite being waterproof, cork can absorb liquid. That can lead to permanent stains.
  • Cork expands and contracts, making temperature and humidity changes problematic.
  • Although it can be replaced, the removal process is not easy. A new layer cannot simply be put over the top of the existing layer.
  • Needs highly trained, skilled professionals to install cork tiles.
  • Though only an aesthetic issue, the colour of cork fades easily as it is very sensitive to light.
  • The little maintenance cork requires must be done properly in order to prevent coating damage. Cork flooring, for instance, must be sealed every five years in order to remain waterproof.
  • In comparison to other insulation options, cork is more expensive. This depends on thickness, density, and location of the material.
  • Plastics are present in the adhesives used to stabilise compressed boards, making them resistant to biologically breaking down at the end of the life cycle.

Cork in a Nutshell

Light, resilient, pliable, a natural insulator, waterproof, and affordable: cork appears to be the wonder construction substance. Sure, there are some downers, but as with any building material, weighing up the many pros and equally important cons ensures you use it in the right way for the best result. And seeing as it’s so durable, it matters not where in the world you are – from hot and dry to cold and damp, cork could be the answer to your sustainable construction dreams.

There’s plenty more to discover about natural sustainable materials in our various other fact files. Take a look at what else we’ve got to offer and see which suits your building project best:

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