What if there was a building material that grew on trees like the sweet and fresh fruits that we enjoy on a hot summer afternoon? The material here presented – cork – does not grow on trees but rather around them. Let’s dig further!
Source
What today is mostly found to be used as a bottle sealant for champagne, wine, and other alcoholic beverages, has been used in varied other applications for over four millennia (1).
National Geographic accounts cork to have been used for “fishing floats and sandal soles, as plugs for jugs and barrels, and as insulation for soldiers’ helmets and beehives”, and literary mentions such as in Virgil’s Aeneid. The use of such material declined with the fall of the Roman Empire to resurface in the 17th century, to meet the most purpose of today.
Where was cork found at the time?
Because cork is the outermost layer of bark of the Quercus suber oak tree, one would have to ‘shave’ with a hatchet that layer of the tree when it reaches a minimal thickness. The tree reached enough maturity for the first harvest at 20-25 years and from then every nine to twelve years (2), until the end of its productive life, at 150-200 years (3).
And no wonder most of the historical reports of cork use come from the Mediterranean region – the Oak tree is native to the dry airy climate of Southern Europe and North Africa. Traces of cork found in the Tejo River basin are dated back to ten million years old (4).
Portugal accounts for the largest producer of cork, supplying more than half of the world’s demand (5). Montados, the oak tree forests in Portugal, account for almost a quarter of national territory, more than 736,000 ha (6). For their substantial size and undisturbed environment between harvests, they are highly important for local ecosystems. Furthermore, are part of the Portuguese cultural heritage and contribute to the regional identity (7)
In North Africa, cork forests are highly important in “preventing desertification by helping to bind the soil and organic substances, which reduces erosion and increases water storage”. Furthermore, they assure employment in such industry, upon more than 100,000 people are directly and indirectly dependent (8).
What Makes Cork Be Considered for Varied Purposes?
The structure of the material – empty cell honeycomb – is what makes it lightweight and lowly dense (9).
Suberin, the main component of the cell membrane (45%), makes cork impermeable to liquids. Because “gas is located in tiny, hermetically sealed cavities” is responsible for poor conductivity in terms of thermal, acoustic and vibration, cork acquires excellent insulation properties (10). The flexibility of the cell membrane accounts for the cork’s mouldability. Furthermore, cork is unaffected by rot or insects while the shock absorption makes cork a great cushioning material.
Any leftover cork can be recycled into agglomerate cork by breaking it into small pieces and ground. Because of the compression at high pressure and temperatures that release the natural biding, there is no need for artificial binding agents (11).
The greatest quality of cork, and highly important for today’s environmental context, is that cork is a natural and renewable material.
The harvest of the cork is an industry that has not yet become automated. Despite technological advances, the delicacy of such a particular harvest assures manual labour for at least a few more decades, contributing to the social and economic spheres of the region. Furthermore, because the older trees are the ones producing thicker and thus better cork, the cork industry is generally more profitable long-term.
What are the Challenges Related to the Use of Cork?
For cork to be harvested, the layer of bark must reach at least an inch thickness, which has become increasingly difficult to attain. National Geographic explains such phenomena as an “adaptive response to higher temperatures, reduced rainfall, and increased exposure to ultraviolet light” (12).
Furthermore, albeit flexible, cork is quite fragile and the environmental costs for worldwide shipping put in jeopardy the environment friendliness of the material.
Cork Applied in Architecture
Wall and Roof Insulation
Critical Concrete, a non-profit organisation taking on challenges linked to the construction industry and aiming for sustainable practices, exemplifies the use of cork as wall and roof insulation in the rehabilitation of a House in Esposende.
The house, like many in Portugal, held no insulation. Furthermore, the group encountered challenges such as uneven walls and sought to avoid glues and mortars often used in cork solutions like in the ETICS system.
The proposal for the roof comprises four layers only – cork panels, vapour barrier, wood and tiles,- and thermal bridges were avoided through the sarking technique.
In another project, the same group adopted cork as an insulator for a 140-square-meter roof.
Cladding
Portuguese architect José Carlos Cruz uses cork as cladding on his project for a Hotel in the Portuguese region of Alentejo.
Spanish practice Estudio Albar, in turn, uses cork as cladding for a house. The qualities of cork as an insulator are explored to such degree that the house Wit meets the Passivhaus standard – a certification given to low-energy buildings with high levels of insulation and airtightness – and requires just three small towel radiators to keep it warm” (13).
However, the use of cork is not limited to the Mediterranean.
Offcieau Architects use cork as cladding in an apartment block in Leuven, Belgium.
Aggregate
Design Studio Niruk develops Corcrete, a multiple award-winning material composed of concrete and recycled cork. Such material plays with the polar qualities of the material – cold/warm, hard/soft – forming visual and tactile stimulating textures. With this material, the duo designs tiles and furniture. The strength of the material is improved by the addition of bamboo fibres as reinforcement, without jeopardizing the environment’s friendliness (14).
João Luís Carrilho da Graça’s project for Lisbon Cruise Terminal (Valmor Prize in 2017, nominated for the Mies van der Rohe Prize, in 2019) also uses cork as aggregate in the walls and façades, reducing the weight of the structure by 40% (15).
Final Remarks
Cork is a material used for millennia and for a good reason! Besides all the qualities advantageous in architecture and construction, cork is a raw material – natural, renewable and recyclable. With the ever-growing concern for the climate, cork holds great potential. Precisely because of its qualities and potential, it ought to be protected.
References:
- Cork (no date) Critical Concrete.
- One can usually recognize a white single number on the bark of a cork tree. Such number indicates the last digit of the year in which the cork was harvested, i.e., if the tree presents a 9, means the last time cork was harvested from that tree was in 2019.
- The story of Cork (2016) Cork Products By Corkway; Cork (no date) Critical Concrete.
- “A fossilised fragment discovered in the Tejo river basin, more than 10 million years old, shows the existence of the cork oak in Portugal dating back to the oldest times. Some researchers believe that this unique tree existed much earlier and estimate its existence to be more than 60 million years.” Cork encyclopedia (no date) Zur Startseite.
- Cork (no date) Critical Concrete.
- Cork encyclopedia (no date) Zur Startseite.
- Cork (no date) Critical Concrete.
- Cork encyclopedia (no date) Zur Startseite.
- “In the cell structure of cork, each cubic centimetre contains between 30 and 42 million cells. The fact that the cork fabric contains 89.7% gaseous substances explains its very low density.” Cork encyclopedia (no date) Zur Startseite.
- Cork encyclopedia (no date) Zur Startseite.
- Cork encyclopedia (no date) Zur Startseite.
- Rupp, R. (2021) Corked!, Culture.
- Jon Astbury |24 January 2024 Leave a comment (2024) Estudio Albar completes cork-clad Casa Eñe overlooking Spanish National Park, Dezeen.
- Corcrete merges recycled Cork and concrete (no date) Core77.
- Architecture and design – architecture and design – business – cork applications (no date) Corticeira Amorim, world’s biggest cork processing group.
References:
Amy Frearson |16 December 2013 1 comment (2019) Jose Carlos Cruz completes ‘World’s first cork-clad hotel’, Dezeen. Available at: https://www.dezeen.com/2013/12/16/ecork-hotel-in-evora-by-jose-carlos-cruz-arquitecto/ (Accessed: 28 January 2024).
Architecture and design – architecture and design – business – cork applications (no date) Corticeira Amorim, world’s biggest cork processing group. Available at: https://www.amorim.com/en/business/cork-aplications/architecture-and-design/38/ (Accessed: 28 January 2024).
Building with cork (no date) Critical Concrete. Available at: https://criticalconcrete.com/building-with-cork/ (Accessed: 28 January 2024).
Corcrete merges recycled Cork and concrete (no date) Core77. Available at: https://www.core77.com/projects/59377/CORCRETE-Merges-Recycled-Cork-and-Concrete (Accessed: 28 January 2024).
Cork (no date) Critical Concrete. Available at: https://criticalconcrete.com/cork/ (Accessed: 28 January 2024).
Cork encyclopedia (no date) Zur Startseite. Available at: https://www.corklife.com/cork-encyclopedia/ (Accessed: 28 January 2024).
Jon Astbury |1 October 2022 Leave a comment (2022) OFFICEU architects unites cork-clad housing blocks in Belgium with communal living areas, Dezeen. Available at: https://www.dezeen.com/2022/10/01/officeu-cork-clad-de-sijs-co-housing-belgium/ (Accessed: 28 January 2024).
Jon Astbury |24 January 2024 Leave a comment (2024) Estudio Albar completes cork-clad Casa Eñe overlooking Spanish National Park, Dezeen. Available at: https://www.dezeen.com/2024/01/24/estudio-albar-cork-casa-ene-spain/ (Accessed: 28 January 2024).
Rupp, R. (2021) Corked!, Culture. Available at: https://www.nationalgeographic.com/culture/article/corked (Accessed: 28 January 2024).
The story of Cork (2016) Cork Products By Corkway. Available at: https://www.corkway.com/articles/the-story-of-cork/ (Accessed: 28 January 2024).
