Rubber tile

Rubber tile flooring was first used in 1894. Rubber tile flooring could be synthetic or organic and was possible of being installed in three different manners. Rubber tile, sheet rubber, and interlocking tile are the most common forms of rubber flooring produced, with interlocking tiles being the most dominant. Rubber tile flooring is known for its sound-deadening qualities and its resiliency. It was also popularized for its hygienic and water-resistant abilities.

History
Vulcanization was developed in 1839 by Charles Goodyear. Vulcanization was the curing of rubber using heat and sulfur, which helped prevent the rubber from deteriorating in heat or cold. The discovery of vulcanization made it possible to use rubber in a variety of products. The late 19th century brought a higher demand for tires and an increase in knowledge of rubber. New technologies caused the rubber industry to grow, resulting in several new products including rubber flooring. Before rubber flooring, several attempts to produce waterproof flooring had failed. Some of the first attempts to make waterproof flooring used a combination of painted floor cloth that used canvas, wallpaper, and a rubber varnish. Other attempts combined materials like India rubber or fibrous materials that were rolled into sheets, heated, and then painted. Frank Furness was the first to patent interlocking rubber tiles for interior use in 1894. The New York Belting and Packing Company claim they were the first to manufacture the interlocking tiles. The first tiles were roughly 2 inches square and 3/8 inch thick. The friction fit of the interlocking tabs held them in place. 7 years later, Goodyear was producing its own version of the interlocking tile. Goodyear and other companies later suspended the production of interlocking floors. Goodyear started production of hard sheet rubber flooring in the 1920s, modeled after the product of the North British Rubber Company’s block rubber flooring. Goodyear led the way for sheet rubber flooring. With an improvement in adhesives, the sheet rubber flooring could now be glued directly to the substrate. Sheet rubber flooring was more expensive than most other flooring types at the time and were limited to 4 ½ feet wide. Rubber tiles later became popular. These were formed by cutting sheets or casting in molds. These tiles were ideal for large spaces and could come in a variety of styles or patterns, including solid, paisley, or marbleized.

Manufacturing Process
The first rubber floors were organic and made of a mixture of pliable materials. Rubber, clay, chalks and materials (asbestos or ground wood) were added. Also, processing oils and organic pigment were added. The rubber usually made up less than 25%, which decreased the cost while increasing the durability. Synthetic rubbers were first introduced in the 1930s and were more resistant than organic rubber flooring. They were less likely to deteriorate from contact with oxygen, ozone, solvent attacks, or oil stains. Manufacturing began with rubber dough that was a result of either natural or synthetic rubber that had been curdled. It was mixed with additives for color and strength and then the compound was rolled into thin sheets that would later be vulcanized. The dough was left in dry storage until it was needed. Dough was sent to a compounding room to get fillers, pigments and vulcanizing agents added in appropriate amounts. Most company’s kept this room protected to keep their secrets of the compound’s makeup. The dough and its additives were mixed in a mill then dusted with talc powder and stored before calendering, cutting, or molding. The calender machine was run by steam and had at least two rollers that would heat and roll the compound rubber into thin sheets. These machines used the distance between rollers to determine the thickness of each rubber sheet. Curing then occurred on the calender or a draw-out table where heat and pressure could be applied. Interlocking tiles were originally cut from sheets of rubber by a die. These sheets were usually cured under heat and pressure though steam set molding was also possible. After curing, the pieces were cut into squares of particular sizes.

Uses and Installation
Interlocking tiles were ideal for kitchens and boats because of their waterproof qualities. Also, these tiles were known for being quiet and extremely flexible. Larger tiles were easy to maintain and exceptionally durable but were best known for their design potential and resiliency. Rubber tiles were popular for automobile showrooms, banks, libraries, and churches. Rubber was also used around electrical equipment because of its insulating abilities and in hospitals for hygienic properties. Interlocking tile measured 2 inches overall and was usually assembled in a mosaic form with a variety of colors. The use of dovetail connectors or male/female connectors made for easy installation. Tiles usually came in one of three shapes: square, triangle, or rectangle. The traditional colors were black and white though reds, greens, blues, and yellows were also quite popular. Rubber tiles were commonly cut from rubber sheets and were the most successful of the rubber flooring products. Rubber tiles grew in popularity because of their infinite design abilities. The checkerboard style floor became the most popular application of rubber tiles with herringbone and basket weave closely behind it. Tile patterns were usually surrounded with a border that was also made of rubber but usually had a different pattern or color to distinguish it from the main tile portion. Goodyear offered a variety of colors but three specific thicknesses of 3/16, ¼, and 3/8 inches. ½ inch tiles could be specially ordered but cost more. Square tiles were normally found in 4, 6, 12, 18, and 24 inches while rectangles were 6 by 12, 9 by 18, or 12 by 24 inches. Custom sizes could be cut and would likely cost more money. ¼ thicknesses were the most popular because anything more proved difficult to cut more than 9 inch diameter. Interlocking tiles made installation easier, requiring no mastic and little or no glue. Rubber tile installation was often compared to linoleum installation. Rubber tiles could be installed on concrete or wood subfloors if they were smooth and clean. In the 1930s, the introduction of felt to the installation process made for more absorptive flooring with less differential movement in the rubber tile. First, the felt was applied to the subfloor, usually with some type of adhesive. Then, a rubber or adhesive cement was applied to the felt, the tiles were laid on top, and a roller of heavy steel or iron was rolled across the top of the tile. The rolling began about half an hour after the floor was laid and should have lasted about 15 minutes for each section to remove air bubbles. The floor was the left for five days to allow the cement to cure and was then gently washed or polished according to manufacturer’s instructions.

Conservation
If rubber flooring has been maintained, it is usually rejuvenated by cleaning or rewaxing. If the rubber flooring has been severely neglected, it may be impossible to save. Rubber tiles are likely to break down and disintegrate when not properly taken care of.

Deterioration
All rubber floors are susceptible to deterioration when exposed to heat, light, abrasions, and chemical reactions. The use of sulfur during vulcanization may continue to interact with the material long after it leaves the factory. Sulfur can cause rubber to dry out or cause the chemicals in rubber to move towards the surface (called a bloom). Oxidation increases brittleness, which results in a process called shelf aging. Shelf aging is caused by lights, heat, or metal interactions. Chalking occurs when the rubber flooring is exposed to inorganic fillers. This process will cause the rubber to deteriorate and become dull. Copper and fatty acids have been known to cause damage in rubber flooring as does improper cleaning that has softened the rubber until it is sticky. Rubber may also be affected by oils, solvents, and petroleum-based products. These products will cause the floor to soften and often results in staining.

Conservation Techniques
When beginning a conservation treatment, it is important to determine the polymeric composition and curing system used in the creation of the rubber flooring. Laboratory testing is often helpful in determining various compounds but is destructive to the material. Using a scanning electron microscope can x-ray a sample of rubber flooring even under a protective coating. If sulfur is present, the flooring has undergone vulcanization; aluminum and silica is evident of earth fillers. Inconspicuous areas should be the donors of sample pieces, as these samples may become damaged in testing. These tests may also suggest what types of cleaners to avoid. The alternative to testing is using a mild cleaning emulsion wax and a light buffing to clean the area. Chemical solvents should be applied in small amounts to hidden areas and then wiped away quickly, as should any cleaning solvent, to prevent damaging the rubber under the foreign substance being removed. Frequently sweeping and occasional damp mopping is suggested. Ammonia can be used in a small dose with cold water but should not floor the floor to avoid penetration of seams. Sponge mops are suggested to help control the flow of water. Red and green tiles are likely to bleed when they first come in contact with water. Vegetable soap or Ivory soap can be used to remove stubborn dirt; abrasive cleaners should be avoided because they can eat the cotton fibers and dull the finish. Turpentine and pine cleaners are likely to make the rubber sticky and can permanently damage the chemical composition of the floor. Conservation is possible with protective agents (antigradents) or protective barrier coatings. Antigradents are made of amines and phenols but is not a practical solution for architectural applications. Protective coatings of wax or polish are better applied in architectural applications. These protective barrier coatings can reduce the oxygen diffusion in flooring and can serve as a barricade between the floor and oils and acids. Waxes and polishes are the easiest solution to a dull or dry floor. Waxes and polishes may present certain problems such as solvent attacks. Waxes should be water-based emulsion floor polish because these can usually be applied without buffering. Hard paste wax can be applied using a light buffering but only over a water-based emulsion polish. Paste wax may contain petroleum distillates, which has been proven to damage rubber flooring, so a test area is highly recommended. Hot water should never be used as should modern acrylic floor finishes. The best way to approach historic rubber flooring conservation is by treating the flooring in place. Rubber floors over time become brittle and may crack or break upon removal.

Replacement
Because rubber floor tiles are still produced, deteriorated historic pieces may be replaced by a new piece that is close in color and size. Solid and marbleized tiles are still produced by several manufacturers. If the new tile piece is not the same thickness, layers of subflooring can be added to make the floor level. Relocating interlocking tiles may be easy if they have not been glued to the floor. Switching hidden pieces (under furniture or rugs) with damaged pieces from the same room is an easy solution. Custom tiles can be created both in rubber or synthetic materials. Custom interlocking tiles can be made using a die-cut process from existing square tiles. It may be possible to get replacement pieces that are the approximate color or appearance of the historic piece.

Standards and specifications

 * ASTM F1344 - 04(2009)e1 Standard Specification for Rubber Floor Tile
 * ASTM D1566 - Terminology Relating to Rubber
 * ASTM D2240 - Test Method for Rubber Property--Durometer Hardness
 * ASTM F-710 - Standard Practice for Preparing Concrete Floors to Receive Resilient Flooring
 * ASTM F-1482 - Standard Practice for Installation and Preparation of Panel Type Underlayments to Receive Resilient Flooring
 * ASTM F-1869 - Test Method for Measuring Moisture Vapor Emission Rate of Concrete Subfloor Using Anhydrous Calcium Chloride
 * ASTM F-2170 - Test Method for Determining Relative Humidity in Concrete Floor Slabs Using In Situ Probes
 * ASTM F-2420 - Standard Test Method for Determining Relative Humidity on the Surface of Concrete Floor Slabs Using Relative Humidity Probe Measurement.
 * ACI 302.1R - Guide for Concrete Floor and Slab Construction 117R Standard Tolerances for Concrete Construction and Materials
 * Resilient Floor Covering Institute (RFCI) Recommended Work Practices for the Removal of Resilient Floor Coverings
 * MASTERSPEC Guide Spec Section 03300, “Cast-In-Place Concrete”