When it comes to choosing a sustainable, renewable, versatile material to employ in the service of green design, it would be hard to do much better than cork. Cork has been used since ancient times for such items as sandals, wine and oil cask stoppers, fishing floats and even insulation. Now architects and interior designers are finding cork to be a valuable modern construction and finish material as well.
Commercial cork is produced primarily from the cork oak tree that grows throughout the region ringing the Mediterranean Sea, and is harvested from the excised bark of the tree. Today, Portugal is the global leader in commercial cork production.
Cork is a rapidly renewable and sustainably produced product, for, by law, the bark of a cork oak tree may only be harvested at nine year intervals, beginning only after that tree has matured to a trunk circumference of about 30 inches. As these trees may survive to ages approaching 300 years, and are never harmed by their bark removal, they serve as a continued consistent resource. In fact, over the past century, the Portuguese cork oak forests have more than doubled in size. Bark removal is done by hand, as it has been throughout time, and the trees are thus treated gently.
The greatest global use of cork today is still as stoppers for wine bottles and other casks. Much of the cork used in the composition of floor tile or other construction materials is comprised of the ‘waste’ from stopper production.
Cork’s peculiar composition makes it an ideal green material. First, cork is durable with a long service life, and can be fairly easily repaired. In the U. S. today, there are buildings that have in-place cork flooring nearly 120 years old. Second, cork is comfortable, as the material is honeycombed with millions of separate air capsules, which lend a certain amount of flexibility and give. Cork flooring is thus very comfortable for the walking or standing user. Those air cells also recover their shape after deformation, giving cork a self-healing nature.
Third, those same air cells — and the waxy, moisture-resistant membranes that separate them — make cork a marvelous insulator. It resists not only the transmission of heat, but also that of sound and vibration. Cork’s insulative and cushioning properties have made it very popular as a finish material for sound studios and performance halls and over radiant hot water heating systems, and as a cushioning pad beneath heavy machinery and building equipment. Cork used for its insulative properties is best acclimated to its eventual environment for a period of several days, to allow the cork’s air cells to adjust, via expansion or shrinkage, to their eventual configuration. This will eliminate any minor cosmetic defects upon installation.
Fourth, cork is repellent to insects, termites, mites, mold, and resists water damage and rotting, due to the waxy substance inherent in the cork membranes. Fifth, this same waxy substance confers fire inhibition, making cork fire resistant. The material also releases no toxic gases. In sum, these various sustainability features mean that cork flooring, for example, can add up to six LEED points to a green project.
Floor tiles made of cork are typically pre-manufactured and pre-glued in modular sizes for ease of installation. Such tiles are suitable for a wide array of building types, including residential, retail, commercial, educational and hospitality uses. The greenest tiles use water-based contact adhesives, with no off-gassing VOCs. The most common (and most versatile) cork tiles are 3/16” thick, and are available in a broad range of sizes, shapes and colors. Though cork is water resistant, cork flooring in wet areas should have a top coat to prevent any water from affecting the water-based contact adhesive holding the cork tile in place. Cork flooring may installed over virtually any well-prepared subfloor, provided it is sound, solid, level, clean and free of objectionable materials.