Cork oak, material for flooring, sound insulation and stoppers

Cork isn't just bottle stoppers, although that's what it leads us to think of. Cork is also used as a raw material for flooring, sound insulation or thermal or other objects with various uses. But what is cork and why did it become the subject of Wood Magazine?

What is cork

Cork oak is the bark of a distinctive oak tree native to SE Europe and North Africa and specific to the Mediterranean basin. Quercus suber or cork oak has been known since ancient times, its bark being used by the ancient Egyptians. Fossil traces of the cork oak have been found dating back to the Palaeolithic.

The tree grows approx. 20 m. The bark is harvested without cutting the tree and is replanted over time. On the surface the bark has a thin fire-resistant layer. If the forest is destroyed by fire, the bark will protect the trunk of the oak which will regenerate quickly, unlike other trees which burn completely.

The cork oak is now cultivated in Portugal, Spain, Italy, France, Morocco, Algeria, Tunisia and is protected by law. It can only be felled after it has completed its 200-year life cycle and only with special approval. In Portugal, the main cork-producing country (50% of world production), if one cork oak is cut down, two others must be planted instead.

How to harvest

I told you that the bark is harvested without cutting the tree. It can be harvested for the first time when the tree is around 20 years old. The next harvest can be done after a minimum of 9 years, which is the time needed for the tree to recover. After harvesting, the year is written on the tree so that there is no doubt as to how long it will take. In its 200 years of life, the bark of an oak tree can be harvested about 12 times.

Harvesting is done exclusively by hand and only by people trained not to hurt the tree. A thin, not very large blade is used to make an incision along the tree. The longer the incision, the better. Very carefully peel off the bark so as not to destroy the thin membrane protecting the tree. Tearing it may lead to the death of the tree. The amount of bark harvested at one time increases with the age of the tree. For example, an 80-year-old tree can yield around 200 kg of bark at one harvest.

Cork production is 300,000 tonnes/year, worth €1.5 billion and employs 30,000 people. Only 15% of the bark volume is used for cork stoppers, but this represents 67% of the total value. The main producer of both cork stoppers and other cork products is Portugal.

Properties of the raft

Cork is a material with incredible properties. The dead wood cells that settle on the outside to form the bark settle in the form of a honeycomb that holds a lot of air. This makes the bark very light, its weight being 1/4 that of water. Therefore, it floats very easily and is used to make fishing tackle. In our country, its name is derived precisely from this property of floating.

Also thanks to the air encapsulated has the best insulating properties, both sound and thermal, compared to existing insulation products. As sound insulation cork has a very high capacity to absorb sound and vibration. It is used to clad the walls of rooms where it does not have to produce an echo.

It has an extraordinary power to return to its original form. A piece of cork that is subjected to a very high force of 96,000 kPa in 24 hours returns 90% to its original form.

It is rot-resistantthe jib, does not absorb water and dust.

All these properties are due to the growing area, the Mediterranean climate. At one time, an American investor attempted to acclimatise cork oak in the US. He considered California to be an area with a climate very similar to the Mediterranean and planted oaks there. The resulting bark was very different from that harvested in Europe and North Africa, becoming woody.

How corks and cork boards are made

After collection, the bark is palletised and arrives at the factory. Here it is oiled to be cleaned and disinfected, but also to soften. The soft bark is much easier to work with. As not all bark is the same thickness, the thick bark is separated from the thin bark, which is used to make natural cork stoppers, and the thin bark, which turns into granules and is used to make technical cork stoppers.

Natural plugs are simply obtained by an operation similar to stamping. A machine is used to cut the corks out of the bark, then they are sorted into categories and packed. Some people say that if the bottle has no cork, the wine is not of good quality. It turns out that this is not so and that the cork, unlike the oak barrel, has less influence on the quality of the wine (if any).

The thin bark is turned into granules, mixed with binder and made into a cork agglomerate which is then sliced. These slices are used to make technical cork stoppers, floor boards, cork rolls used for various products (shoes, bags, decorative items, cladding sheets).

From the leftovers of the natural plugs - a rather large quantity, 70-75% - the boards for thermal insulation are made. The scraps are shredded, put into large metal moulds and treated with superheated steam. The heat activates a natural binder in the bark - suberin - which binds the grains together and turns them into a block of expanded material.

Uses

Obtaining cork stoppers, both natural and technical, is the main use for which cork is known. Yet it was used as an insulating material long before it was used as a cork stopper. Houses in southern Italy, France and Spain used to have oak bark on the floor and ceiling. This is how the inhabitants of those areas protected their houses from the scorching heat of summer and the damp cold of winter.

However, its use as an industrial insulation material has arisen due to a worldwide decline in demand for corks. The emergence of plastic, metal and other substitute cork stoppers has led cork stopper manufacturers to turn to other markets. The world's largest cork stopper producer, Amorim company from Portugal, he thought of using the leftovers from natural plugs to make a natural, healthy and high-performance insulation. He has succeeded and has become one of the world's largest producers of natural insulation material, which he now exports worldwide.

Cork is used for flooring, sound insulation, many practical or decorative objects (sheet metal, covers, beads, bags, holders). There are many cork objects that caught my eye, but the Stefan Janoski cork sneakers, which Nike chose to put their logo on in 2015, strike me as extraordinary.