Cork tile

Varnished cork flooring found in a residential bathroom

Cork tile is made of ground cork bark from a cork oak tree. Cork tile could be used for floor and wall tiles. Cork is porous but its cellular structure gives it a resilient property. Cork tiles are generally light weight with high compressive strength and low thermal conductivity.

History

Cork was first developed as bottle stoppers. The recycling or cork soon became popular as it could be used to create other products. Cork waste originally required no further processing to be useful. As more cork products were introduced, ground cork chips and shavings became necessary. Corkboard was one of the earliest developments that used cork waste. Corkboard was used extensively for its insulating properties. Asphalt was initially used to fuse the shavings together but the strong smell left the combination unfavorable for interior use. John T Smith discovered the use of heat to melt resin found in cork which provided a natural binding that held the cork together. This method would later give way to the creation of cork tile flooring. The first cork tile floors were manufactured by the David E. Kennedy Company in 1899, though evidence suggests that Germany may have produced a similar product as early as the 1890s. The Armstrong Cork Company soon became the largest manufacturer of cork tile in 1904 and granted Kennedy Company distribution rights in 1910. Cork tile did not gain popularity as a flooring material until the mid 1920s when the United States was experiencing a building boom. Cork flooring materials owed its prosperity to the additives that made the tile moisture proof, as well as grease, ink and mild acid impervious. Cork tile was at the peak of its popularity the year before World War I.

Manufacturing Process

To begin making cork tiles, cork shavings were ground up and put in cast iron molds. Molds were then compressed and baked in a kiln between 450 to 600 degrees Fahrenheit for no more than 10 hours. A belt moved the molds through the kiln, about 120 feet in 45 minutes. The heat melted the cork resin and combined by the pressure, the cork particles were fused together with no binder or glue. A factory finish of proxylin or nitrocellulose lacquer would partially penetrate the surface, thus making it impervious to moisture or dirt. Waxing cork flooring was completely normal though unnecessary. Phenolic resin was added to the cork mixture after World War II to strengthen the material. These mixtures had to be baked longer at lower temperatures. These tiles were more resilient and less dense that traditional cork tiles. Also, these tiles were more uniformed in color. Cork flooring was usually a natural brown color that could be made darker by hotter temperatures and longer baking times. There were three traditional shades of cork-light, medium, and dark. Tongue and groove tiles were later introduced to the market for easier installation. Cork tiles were sold unfinished for the consumer to install a finish as they saw fit. Literature recommended sanding the tile floor after installation to achieve a smooth finish. Waxing the floor was often done to improve the luster of the material, though it was not necessary. Sanded tiles could also be coated with a lacquer-based sealer followed by a coat or two of wax.

Uses and Installation

Even though cork flooring was mildly expensive, its resiliency made it a popular choice for libraries and schools. Cork tile was promoted for their sound-deadening qualities as well as their physical warmth. One notable use of cork tiles is the 25,000 square feet of cork tile that was installed in the National Gallery of Art in Washington, D.C. Cork tiles were also promoted for being easy to clean and high sanitation properties. Cork, therefore, gained popularity in both residential and commercial buildings. In the late 1930s, cork was still considered a modern material. Several architects like Richard Neutra and Frank Lloyd Wright installed cork tiles in their homes. Cork tiles soon became available in a variety of shapes and sizes. Border strips were developed to encompass cork tile patterns. Tiles were being made as small as 2 by 2-inches and as large as 18 by 48 inches. The standard size of tiles became 9 by 9 or 12 by 12 for squares, 9 by 18 or 12 by 24 for rectangles, and border strips from 3 by 18 to 12 by 36 inches. Because cork is a natural product, expansion and contraction should be expected. Cork should reach its normal point of expansion before it can be installed properly; otherwise buckling is likely to occur. To avoid installing cork tile when it is compressed, it is recommended that the tile be delivered to the site several days before the installation is to take place. The wrapping should be removed and the tiles should be spread out over the floor in the room in which they will be installed. Early cork tile installation has changed since the introduction of the product. Originally, the use of brads and asbestos with concrete was used to keep cork tiles in place. Before the concrete cured completely, a thin layer of asbestos concrete was spread over the floor. Once the material dried, waterproof mastic was applied. The cork tiles were then embedded into the mixture with the joints closed and cemented. Brads were then inserted to hold the tiles in place while the mastic cured. In 1925, the use of brads to install cork tile was still recommended but was replaced by a simpler method that used an elastic waterproof cement to glue the tile to the floor. The tiles were then weighted down to secure them in place while the materials dried. Installation onto a concrete floor requires plaster of paris to fill in any cracks of joints. Portland cement later became an alternative to plaster of paris. The surface was then cleaned and the mastic applied directly to the concrete or glued with linoleum paste to a layer of heavy felt.

Conservation

Cork tiles are susceptible to damage from excessive exposure to moisture, light, grease, and oil staining. Scratches may be removable by machine buffing while small gouges are usually repaired with a ground cork mixture. Cork tiles that have become deteriorated to a point of no repair can be replaced by selecting similar new tiles.

Deterioration

Cork floors are likely to sustain damage over a period of time, especially in high-traffic areas. Cork tiles can be damaged by abrasion from dirt if their protective coating has been allowed to wear off. Wax coated cork tiles are likely to be damaged in exposed to excessive moisture. Moisture can break down the binder and loosen the cork shavings. Tiles experiencing this kind of deterioration are likely to shrink or buckle. All wood products, including cork flooring, can be damaged by the sunlight and will fade over time. Cork tiles are also likely to become brittle and crumbly over a long period of time exposed to sunlight. Because it is so porous, cork flooring is highly susceptible to oil and grease staining. Alkaline cleaners are known to degrade cork. Also, organic solvents and abrasive scouring powders are likely to destroy the structural integrity of cork flooring.

Conservation Techniques

Before developing a restoration plan for cork tiles, it is imperative to identify if it is unfinished or resin reinforced. Dates of installation and construction should provide information about the tile’s makeup. The tile’s finish is another factor to consider. It should be determined if the tile has a wax or polyurethane sealant. Cork tile should also be checked for worn areas, disfiguring stains, and locations of water penetration before a conservation plan can be developed. Cork tiles should be swept with a soft broom and mopped with a damp mop. Mats may ideal in limiting the abrasion caused to a cork floor in high-traffic areas. Stubborn dirt may be lifted out using a paste or liquid wax. This process should be used less frequently. Water in detergents are not normally recommended but a diluted linseed-oil based cleaner and a drop or two of mild phosphate detergent can be used sparingly but should be followed with a rinse of clean water. Using a clean, dry mop to remove excess water and aid in the cork flooring’s drying is strongly recommended after washing with clean water. Resin reinforced tiles are less likely to absorb water and can therefore be cleaned with a damp mop. Infrequently washing with water and a neutral pH detergent is acceptable but excess of both should be quickly removed afterwards. After washing, waxing or buffing is suggested to strengthen the floor. Tiles that have become detached without severe damage can be reapplied to the substrate using a water-based adhesive. Tiles should then be weighted for a 24 hour period to ensure that bubbles will not form and adhesion takes place. Buffing out light scratches from a cork floor is possible by using lamb’s wool pad. Small holes can be patched with putty that contains cork shavings and shellac. Masking tape should be placed around the targeted area to protect surrounding surfaces. The putty is then pressed into the hole and left until it is dry (about 30 minutes). Once the putty has completely dried, it can be sanded with 00 grade steel wool. Clear varnish is applied to match the luster of the existing floor. Sanding is not recommended because it will remove too much cork.

Replacement

Historic cork tiles can be found and should be used to replace only the most deteriorated tiles. Because cork tile is natural material, it is possible to find replacement pieces that are nearly identical to existing pieces in color. Colors may have become faded over time and new pieces should be closely matched to the faded color for uniformity. Sanding down replacement tiles may be necessary to match the height of a slightly warn floor. Tiles should be flush with adjacent pieces to avoid problems. Cork flooring is still manufactured but it is imported to particular suppliers in the United States. Contemporary cork floor tiles are the same shades of light, medium, and dark. Cork tiles can come with a variety of finishes. Unfinished cork tiles are also available. The standard size of cork tiles are now 12 by 12 inches in thicknesses of 3/16 and 5/16. Other sizes and thicknesses may be custom ordered to match historic tiles.

References

• Grimmer, Anne E. "Cork Tile." Twentieth-century Building Materials: History and Conservation. By Thomas C. Jester. New York: McGraw-Hill, 1995. 228-32. Print.