by Christi Graham
What is it?
Most of us don't notice it when we're walking on it, but cork flooring has been naturally enriching interiors for over 100 years in notable buildings such as schools, hospitals, churches, museums, libraries and hotels. It's warm honey-toned appearance, comfort underfoot and ability to soften acoustics often goes unnoticed by those of us who would not otherwise recognize it.
So what is cork? Cork is actually the outer bark of a tree, Quercus suber, which grows in the Mediterranean. Cork oak forests cover approximately 5.4 million acres amongst the seven primary cork producing countries; (30% Portugal, 21% in Algeria, 20% in Spain, 16% in Morocco, 5% in France and 4% each in Italy and Tunisia). Cork forests are carefully managed and treasured in particular by Portugal, which produces 50% of the worlds cork supply.
Cork bark is typically harvested every nine or ten years. After the slabs of cork bark are harvested they are cleaned, boiled and stripped of the rough outer surface. Bottle stopper "corks" are then punched from the best material in the slabs. The remaining scraps are then ground into small granules, mixed with a binder, molded into large blocks and baked in specialized ovens - making use of every scrap of cork bark.
Corks remarkable properties are derived from its cellular structure of hollow, polyhedral (14 sided) cells with extremely strong yet flexible cell walls that are waterproof and airtight. Joined together in a honeycomb like fashion, cork cells produce a very low-density, compressible insulating material. As a floor covering, cork is durable, provides acoustical and thermal insulation, cushions the foot, is resistant to moisture damage and decay and is easy to clean. In addition to all of these features cork is harvested from trees in a sustainable manner - making it very worthy of consideration for use in green building.
Natural cork flooring materials, which we are referring to, are quite different from the widely marketed cork-vinyl composite floor tile. Cork-vinyl products have a polyvinyl chloride (PVC) backing, a cork inner layer and a vinyl surface layer. Due to significant health and environmental concerns with PVC, natural cork flooring is preferred over vinyl.
Cork can be used as a flooring surface, an underlayment for flooring, on walls and ceilings, and is one of the main ingredients in natural linoleum. Cork has been formed into baseboards and moldings as well. In residential applications cork is successfully used in living rooms, kitchens, bathrooms and hallways.
The process of agglomerating the cork requires binders to hold the ground cork granules together. Urea formaldehyde binder was used in the past, (phased out during the 1980's) and today, urea melamine, phenol formaldehyde and natural proteins are more commonly used. Once processed, these are relatively stable binders.
Standard adhesives and finishes are a potential for introducing more volatile organic compounds (VOC's) into the air. It is recommended that you select low or non toxic products for these purposes.
Cork does not offgas or shed microfibers and is naturally moisture, mold, and rot resistant
Corks impact on the environment is quite low due to the sustainable harvesting practices and almost zero waste from the manufacturing process. Producing nations regulate how frequently cork can be harvested in order to minimize damage to the trees. The trees survive the debarking process although they are more susceptible to injury until the protective bark is regenerated.
Most manufacturers offer cork tile in shades of light, medium, and dark, but there will always be shade variation from tile to tile.
Cork is generally available in rolls for underlayment or tiles for floor covering. Tiles are also available as floating floors and include both pre-finished and un-finished parquet tiles. Tiles are available in 12" x 12" x 3/16" and 12" x 24".
For floating floors one manufacturer, Natural Cork, LLC supplies their tiles with a pre-coated contact adhesive. his Natural Cork Floating Floor system is comprised of one by three foot planks consisting of three layers. The surface layer is 100% cork with a UV cured acrylic finish which contains no VOC's. Precut tongue and grooves of the middle layer of MDF form the interlocking layer while the base layer of cork underlayment provides significant acoustical insulation. This brand of floating floors are entirely free of PVC. Available from factories in many patterns and colors, tiles can also be stained for a unique custom color appearance.
Natural cork underlayment is supplied in rolls and sheets for use as acoustic insulation in the installation of hardwood and laminated flooring. Cork underlayment provides over 50db of sound reduction, meeting and often exceeding code requirements.
As the color varies, to achieve best results, shuffle the shade variation prior to installation.
Laying the tile - Natural cork tiles are installed by flooring professionals using adhesives. Most cork tile manufacturers recommend water-based adhesives for this task, which should be fairly stable (without offgassing) after it is cured. However, these adhesives could release potentially dangerous VOC's during installation. Dodge-Regupol, a manufacturer of natural cork, recommends Dri-Tac Flooring Adhesive, which is a water based low VOC, latex adhesive.
Applying the finish - Most cork tiles will require a protective coating. You can finish the floors with either wax or polyurethane sealants. If you choose wax, you can use any paste wax that is recommended for wood floors, however we recommend using a natural wax that has a beeswax base or has low VOC's. For a polyurethane finish 3-4 coats may be required to obtain the finish you desire. Be certain to find a water-based polyurethane finish with low VOC's.
It is recommended by one manufacturer that you do not start the finishing process for at least 5 days after installation. A light sanding may be necessary if you have any uneven areas - these can be corrected by light sanding with No. 80 mesh disc sander (3M) or equivalent.
Routine maintenance is a function of the finish applied.
Waxed finish - Clean with dry or damp mop, occasionally using liquid solvent wax. For a more serious cleaning on standard cork tile, use electric buffing with 00 steel wool discs then apply lamb's wool pads.
Polyurethane finish - Clean with dry or damp mop. To refinish the polyurethane tiles use power floor machine with wool disc (00 grade) and apply polyurethane as directed on container labels.
Performance / Durability
Cork is highly abrasion resistant on it's own and treating it with a protective finish further increases its durability. Cork has a tremendous amount of "memory" and recovers well from compression. Cork floors will last as long as most hardwood floors.
If anyone in your family has a sensitivity to formaldehyde, you might consider sealing your floor with a non toxic sealant that minimizes the "off gassing". (Are there any that are made without formaldehyde?)
Who Makes It
Dodge Cork Tiles - by Dodge-Regupol, Inc.
All Natural Cork Floating Floor and Parquet Tiles - by Natural Cork, Ltd Company
Prontokorq - by Korq, Inc.is a tongue in groove floating cork flooring product that comes in 3/8" x 12" x 36" planks. Cork floor tiles measure 3/16" x 12" x 12". Both products are prefinished with a water-based varnish. Korq also offers baseboard and molding products made from agglomerated cork.
Just like any other flooring material, cork can be punctured by sharp objects and damaged by furniture feet. Protective pads under furniture are recommended.
If installing cork flooring in a bathroom take additional measures, such as caulking the perimeter of the room prior to installing baseboard, to avoid moisture penetration.
Environmental Building News, Volume 5, No. 1 - Jan/Feb 1996
Dodge Cork Tile 09650/DOC - Dodge-Regupol Inc. product literature
Natural Cork L.L.C. product literature