by Nick Gromicko, CMI®
While better known for its use as wine stoppers and for bulletin boards, cork is also used for flooring and other building components.
A renewable resource, cork is actually the bark of a species of oak tree, Quercus suber
that grows in the thin, dry soils of western Spain and Portugal. The trees are harvested periodically throughout their lifetimes in a sustainable fashion that does not harm the tree or result in deforestation.
To prepare the bark for commercial applications, it is first cut and removed, then dried, cleaned, fumigated and straightened. While most cork winds up in wine bottles, a portion of the material is allocated for use in buildings, such as flooring, seals, gaskets, expansion joints, intumescent strips, and even external cladding.
Unique Advantages of Cork Flooring
Air pockets allow cork flooring a unique and easy elasticity compared to other materials, which makes it ideal for installation in kitchens, where standing for long periods is common. These air pockets also protect dropped objects from breaking and keep floors at an even temperature, which contributes to a building’s overall energy efficiency. Proponents of cork flooring claim that it's also sound-absorbent, anti-vibrational, fire-resistant, anti-static, mildew-resistant, insect-resistant, and anti-microbial.
Despite these strengths, cork is prone to the following defects and forms of misuse:
- moisture damage. If cork flooring gets wet, it will expand, become uneven, and potentially crack, once dried;
- surface damage. Heavy, pointed objects, such as high-heeled footwear or dogs’ and cats’ claws, can create permanent dents and scratches in cork floors. These impressions cannot be easily sanded away the way they can in wood flooring;
- color fading, typically a yellowing, which will occur when the flooring is exposed to sunlight for prolonged periods of time. Area rugs and large furniture will block light exposure and may create uneven discoloration;
- off-gassing from the binders and adhesives used in cork tiles. Homeowners may purchase solid cork tiles with low-VOC adhesives as a more natural, non-toxic alternative;
- improper use. Due to moisture concerns, only floating-floor cork designs should be used in basement floors. Floating floors may, however, create problems when installed over radiant heating systems, although homeowners may check with the flooring’s manufacturer for specific installation restrictions. For instance, bathroom installations may require that the perimeter of the floor be caulked prior to installing the baseboards to avoid moisture penetration; and
- installation defects that represent trip hazards, as well as cosmetic blemishes, such as:
- bond failure, in which poor adhesion to the subfloor will result in lifting at the joints of the cork tile. The lifted surface can be forced flat under pressure, but this fix is often only temporary;
- sliding, where the tiles slide out of alignment with each other. This is caused when tiles are laid on wet adhesive, allowing them to move as the installer stands on top of them. Installers should let the adhesive dry before stepping onto the tiles. A rectangular gap known as a window can be created where adjacent tiles slide vertically and horizontally, revealing the underlying subfloor;
- waves or undulations, which are unsightly and might cause furniture to sit unevenly; and
- debris beneath the tile, which causes the tile to lift above any object that was not removed from the subfloor before the tile was installed.
Cork floors are available in glued and glueless forms. Glued floors are made up of tiles that are glued down to the subfloor. They are more appropriate for bathrooms because of the protection offered by their polyurethane coating and the absence of the fiberboard core on glueless planks that can be damaged in wet environments. Glueless cork floors, similar to laminate flooring, are fused to a high-density fiberboard core to form planks that can be snapped together. These are suitable for below-grade applications, such as in basements. Cork flooring products range in thickness from 3/16- to 7/16-inch and tend to have natural color variations but can be purchased in light, medium or dark tones.
Tips for Homeowners
Inspectors can pass on the following care and maintenance tips to their clients:
- Keep the floor surface free from dirt and grit through regular mopping with a well-wrung mop. Clean up spills quickly and never use harsh, abrasive cleaners.
- Place entrance mats at doors in order to prevent dirt and moisture from being tracked in and onto the floor. If the mat gets wet, however, remove it from the floor.
- Furnishings and floor coverings should be moved periodically, and heavy curtains or window shades can be used to prevent discoloration and fading caused by intense sunlight through the windows.
- Place furniture rests beneath furniture legs to protect the floor from indentations.
- Periodically apply urethane or polish to eliminate small scratches.
In summary, cork flooring, when installed and maintained properly, is a unique alternative to conventional flooring materials, such as wood and vinyl.