Many people think of cork, if they consider it at all, as a relatively new and possibly unproven surface flooring option. Yet, there are examples of cork floors in public buildings, such as the Library of Congress, that were installed more than 100 years ago and are still in use today.
A proud history
A member of the beech family, the cork oak tree grows in coastal regions of the Mediterranean. Relatively slow growing, these trees survive harsh conditions in depleted soil that supports little else of value. Some cork oaks live to be 400 to 500 years old, though the average life expectancy is 100 to 120 years.
Unlike most trees, whose primary value is derived from lumber, cork is obtained from the bark of the tree. This unusually thick bark is made up of millions of tiny prism-shaped air pockets that produce a resilient cushiony surface and lead to the assertion that, with a cork floor, you are literally "walking on air." Cork is grown on farms and harvested every nine to 11 years. Rather than felling these trees, cork farmers try to keep them alive and producing for generations.
Cork has a long and distinguished history as an agricultural product. In ancient times, it was used for sandal soles, food storage vessels and floats for fishing nets. The seventeenth century French monk, Dom Perignon, is credited with being the first to recognize its suitability for containing sparkling wines, establishing the cork bottle-stopper industry. Over time, cork became more important as a cash crop, resulting in governmental regulation offering protection and placing restriction on ownership, production and harvesting.
Figure 1. Consumer demand drives cork flooring into many non-traditional applications.
The flooring option
The ability to use cork in flooring applications wasn't discovered until the 19th century, when an American, John Smith, discovered agglomerated cork. Today, cork flooring is produced from the post-industrial byproduct of the bottle-stopper industry. This "waste" material is ground up and reformed into sheets, using minimal amounts of adhesive to bind the particles together under high pressure. The size, quantity and type of cork granule, in conjunction with varying degrees of pressure, make the difference between "bulletin board" material and a surface suitable for flooring applications.
Historically, cork floors were finished just as any other wood floora paste wax was buffed into the surface. However, this labor-intensive maintenance was viewed as a real drawback when rolled sheet vinyl and similar "modern" resilient surface options came on the market in the middle of the past century. Cork flooring fell out of favor and, for perhaps 30 years, was not readily available to the general public.
During the past decade, new finishing techniques and improved technologies have revived interest in cork flooring. Though still a small fraction of the overall floor covering market, cork is enjoying a surge in popularity, driven in large part by consumer demand (see Figure 1).
What does cork have to offer that sets it apart from other surface flooring materials? Quite a bit, it turns out. In fact, no other floor covering can match the combined benefits of cork.
Comparisons
Carpet: When it comes to soft surface flooring, carpet is the obvious choice, but it has drawbacks, particularly in an industrial environment. Carpet fibers absorb liquid and conceal grit and microorganisms, making carpet difficult, if not impossible, to clean. While cork may not be a soft surface, it's a resilient one that provides many of the same benefits associated with carpet. Cork is warm, quiet and gentle underfoot. Furthermore, the inherent anti-microbial characteristic of cork makes it a natural in applications where health and hygiene are matters of concern.
Ceramic tile or concrete: No commercial/industrial flooring surface can match the virtually indestructible and solid, reliable, easy to maintain characteristics of ceramic tile and concrete. On the other hand, these materials definitely have their negatives. These hard surfaces are loud and produce echoes. They are unforgiving to both objects and people, causing damage to dropped materials and fatigue when workers must stand on them for any period of time. In contrast, cork provides a cushioned surface that places low stress on joints, feet and back. Cork's use as sound insulation is testimony to its value in a commercial or office environment.
Hardwood: Considered an all-around, good general purpose flooring material, hardwood is a repairable classic that won't go out of style. Wood is readily available in a variety of widths, installation options and designs. Many of these same benefits carry over to "the other wood flooring," cork. Cork can be finished and re-finished in the same manner and using the same products as those applied to any other wood. Unfinished cork can be stained, bleached, pickled, painted, etched, inlayed or installed with a border or in a parquet pattern. Truly, the possibilities are endless.
On the down side, wood that is either waxed or finished with polyurethane can be difficult to maintain to its "just installed" beauty in a shop environment. Often an annual re-application of polyurethane will require at least 48 hours of down time, while wax maintenance entails on-going intensive upkeep. In addition, wood flooring can become distorted when exposed to moisture continuously. These realities apply to cork as well.
A standout advantage is that cork doesn't spread flame and is, in fact, rated as a fire inhibitor.
Vinyl and vinyl composition tile: The youngsters of the floor covering market, vinyl and vinyl composition tile, take little time to install, are impervious to most sources of moisture and are relatively inexpensive. They also come in a wide range of colors and patterns. Durability is a concern, since scratches and dents are not easily repaired. On this issue, cork comes out ahead because scratches can be treated with wood filler and cork's prism-shaped structure means dents will automatically recover fully.
Subfloor preparation is often viewed as a drawback in vinyl systems. Even a slight imperfection in the substrate will telegraph, often in an exaggerated way, through these products to the surface. Therefore, it's important to give considerable attention to repairing, leveling and cleaning the subfloor before application. This strategy also is necessary with glue-down cork tile because of its relative thinness and flexibility. However, cork is also available in a rigid plank format that doesn't require similar attentions.
Figure 2. Cork underlayment provides sound insulation and a resilient surface.
Product selection
The basis for cork flooring is agglomerated sheet material produced mainly in Portugal and Spain. The material looks like what it is: compressed granules. To achieve a different appearance, it's necessary to laminate a thin veneer layer of cork on top of this core material. Lamination takes place at the time of original production, so the thin layer is inseparable from the core. The veneer produces the pattern. There are many patterns to choose from, from bamboo look-alike to surfaces that mimic marble and much in-between.
Tile: Glue-down tile, often referred to as parquet, is generally available in a range of patterns and colorsfinished or unfinished sizes of 12 inches by 12 inches and 12 inches by 24 inches are standard. It's possible to order other sizes as large as 36 inches by 24 inches, the limit of the production machinery. However, larger tiles tend to go out of square easily. Tile can be installed over wood or concrete substrates that meet the qualifications for sheet vinyl applications. The preferred method of adhesion is water-based contact cement, however, other adhesives also can be used. Installing cork tile below grade is not recommended.
Plank: When applied to cork, the term plank refers to a floating floor installation in which cork has been laminated to a fiberboard center core having a tongue-and-groove edge. This offers several advantages:
Underlayment: Subfloor preparation is less stringent.
What to look for:
The floor "floats" and is less visibly affected by expansion and contraction common to wood products.
Product density translates to product durability, with higher density meaning stronger product. Cork flooring should have a minimum density of 28-pounds-per cubic foot, though densities as high as 34-pounds-per cubic foot are available and offer better wearability.
Plank can be installed below grade.
Cork can be purchased unfinished but, unlike some wood, it must be finished during installation. Though some users continue to prefer paste wax, the most common finish today is polyurethane. Cork having a low-maintenance vinyl coating can't be refinished or easily repaired.
Installation is relatively quick.
The thickness of the cork wear layer has less to do with durability than does the material's density. However, thicker cork layers improve insulation, both acoustic and thermal. A good standard thickness is 5/32 inch (4 millimeters). Again, other thicknesses are available, and particular needs can be met through special order.
Thicker product provides better insulation.
"Green" consideration
As is common with other floating products, cork plank requires a perimeter expansion space that will be covered by baseboard or other trim.
Cork is a readily renewable resource that qualifies for Leadership in Energy and Environmental Development credit and contributes to improved indoor air quality.
This product is used specifically for its acoustic insulation properties. Available in both rolls and sheets, underlayment is used beneath other flooring types to reduce noise transmission and impact sound (see Figure 2). With ceramic tile, cork underlayment can also reduce stress cracking.
Wendes Jones is Marketing Director for Natural Cork, Inc., Augusta, Georgia. She can be reached at [email protected] and (866)363-6334.