Cork is the outer bark of the cork oak tree, quercus suber, which grows mainly in the Mediterranean region.
The bark is a vegetal tissue composed of an agglomeration of cells filled with a gaseous mixture similar to air and lined with alternating layers of cellulose and suberin.
Cork’s elasticity, combined with its near-impermeability, makes it the perfect material for making bottle stoppers, floor tiles, insulation sheets, bulletin boards and other similar products.
Because of its remarkable qualities, cork is used in high-tech applications including car engines, dam mechanisms and airport runways. The aeronautics has used cork as a thermal insulator in space shuttles.
The use of cork as a raw material dates back to Phoenician and Greek times. Cork began to become known all over the world as an effective bottle stopper for wine. In fact, cork is the only material that makes a perfect seal during the ageing of the wine.
Cork oak forests cover approximately 2.5 million hectares across the Mediterranean region and most of them are located in seven countries: Portugal, Algeria, Spain, Morocco, France, Italy and Tunisia.
The tree has a life span of 250-350 years. Each cork tree must be 20 to 25 years old before it can provide its first harvest of cork bark. This cork is known as virgin and has a hard and irregular structure. After the virgin cork has been stripped, a new layer of cork begins to grow.
The first of these layers, harvested after nine years, is called secondary cork.
A typical tree produces several hundred kilograms of cork at each harvesting and will survive for many generations. The bark is stripped off the tree in sections by highly skilled men using special axes, a traditional manual skill that dates back many hundreds of years.
Cork is harvested on a sustainable basis and the stripping of the bark does not harm the tree in any way. The bark grows back completely, taking on a smoother texture after each harvest. A cork oak tree can be safely harvested up to 20 times during its life cycle, making cork a truly inexhaustible natural resource.
In a context of increasing concern for the environment, cork remains the only tree whose bark can regenerate itself after each harvest — leaving the tree unharmed. It is truly a renewable, environment.
The bark of the cork oak tree has a unique honeycomb structure composed of tiny cells. Each cell has the form of a 14-sided polyhedron and the inner cell space is entirely filled with an air-like gaseous mixture. The properties of cork derive naturally from the structure and chemical composition of its extremely strong, flexible cell membranes, which are waterproof and airtight.
Because about 89% of the tissue of the bark consists of gaseous matter, the density of cork is extremely low, in the order of 0.12 to 0.20, a fact that bears witness to the huge disproportion between the volume and the weight of the material.
Cork provides ecological insulation because its harvesting does not require the removal of trees. In addition, the process of manufacturing our pure expanded cork panels is a process requiring no other component than cork and water. The various manufacturing steps are defined below.
This debarking is carried out on the trunk and the main branches without killing or injuring the tree. The debarking height depends on the diameter of the cork oak; the bigger it is, the higher the cork can be lifted. A bark coefficient is used which, multiplied by the circumference of the cork oak measured at 1.30 m, indicates the maximum height of harvest not to be exceeded. The duration of reproduction of the cork on a barked tree is around 10 years. Lifting is carried out from May to August. The average lifetime of the cork oak is around 150 years and therefore allows about 15 levies.
After debarking, the cork boards are stacked on specific areas.
They will remain exposed to the open air, the sun and the rain at least 6 months. During this rest period the cork undergoes various transformations which improve its quality such as its elasticity.
During this stage the cork boards are crushed to obtain cork granules. During this stage cork waste from the cork industry as well as the recycling of cork products can be incorporated. At the end of this stage we obtain the cork pellet that we can market in the form of bags allowing the insulation of the attic or low floors.
The manufacture of the cork plates is carried out by placing cork granules in an autoclave furnace and exposing them to superheated steam at 300 ° C. for 20 minutes. Under the effect of heat, the cork granules will expand by about 20% and will reject a glue naturally present inside the cork (the suberine) which will agglomerate the granules together to finally form a block of pure agglomerated cork.
Finally, the block of cork is then cooled with water injection and then mechanically cut into panels of different thicknesses to obtain the pure agglomerated panels that we can directly use.
Cork, by its performance, meets many uses in the building beyond the insulation alone. Indeed, the cork has elastic properties, acoustic, antistatic, antiallergic. It is also easy to maintain, is resistant to mold and fire.
Removing cold wall effects thanks to low effusivity, it has a very high comfort used in floor tiles or wall coverings. It is a very good sound insulation which makes it an interesting insulation on the floor. It can be used as an insulator for buried walls or wet rooms. The cork in plate having a phase shift of more than 12 h for R = 4 m2.K / W (15 cm), it makes it possible to ensure a good comfort of winter and summer for arranged attic.
Cork to all floors !
Cork has a remarkable combination of properties that has made it preferable to make wine stoppers as well as other applications such as thermal and acoustic insulation. Because of its quality of resilient and antiallergic material, it is supple to the walking and brings an unmatched everyday comfort, even by synthetic materials. It is widely used in Northern European countries, the United States and Japan.
The table below summarizes the main cork characteristics known so far :
|Renewable / Recyclable||Mechanical resistance|
|Thermal / Phonic insulation||Anti-allergen / Biodegradable|
|Rot-proof / Durability||Low-density / Buoyancy|
|Good elasticity / Anti-vibratoire||Thermal inertia (Comfort in summer)|
|Water repellent (mold-resistant)||Repellent against parasites and rodents|
|Low flammability||Good resistance to acids|
Apart from dust, safe and easily removed by suction, resulting from the sawdust, cork is safe for the body.
Unlike other products, it is not fibrous and therefore does not emit fine particles.
The odor caused by the cooking cork disappeared at the end of a few months.
Because of its non-adjuvant manufacturing process, the expanded black cork emits neither VOC (Volatile Organic Compounds) nor formaldehyde. Moreover, the cork is resistant to parasites, rodents, termites and fungi (does not mold).
Cork is hardly combustible. In the natural state, cork protects the vital parts of the tree during a forest fire. Cork is carbonized but life is protected.
When used as insulator, in the event of a fire, it does not spread flame and neither emit toxic gases.
Cork is a material that does not deteriorate in time.
It is the only vegetable insulation that is rot-proof even in the event of prolonged moisture. It is also very difficult to degrade by rodents. Finally, it ensures good dimensional stability and compressive strength.
Almost unalterable, cork was found intact during the demolition of the cold rooms of the “Halles of Paris”. This cork set up a century ago was in near mint condition!
Halles de Paris
For more information about the cork material, we suggest the site of the Mediterranean Institute of Cork.