Two Marble Floor Polishing Methods
Author:vian Date:2009-2-23 20:08:12 Read:139
Prior to the past 15 years, Marble was largely reserved for commercial and public buildings, monuments and a very small number of supremely expensive, private mansions. In these applications, the marble was scrubbed with soap and water while it slowly lost its luster. Recently, marble has become affordable to a new class of corporate executives and entrepreneurs with aspirations to live well and display their success. These newly wealthy believe that the appearance of their homes reflects on their success, so dirty, stained, and dull marble just will not do.
Maintaining marble floors to a new standard of beauty requires new knowledge and new materials. Two distinct methods have evolved to maintain the acres of marble flooring installed in homes and commercial buildings in recent years. One method is based on the traditional method of grinding a new surface while the other method relies on a chemical reaction to increase the reflectivity of the marble surface. Both methods require a through cleaning of the marble surface and meticulous precautions to protect the surroundings. Although the traditional method appears messier because of the copious quantities of wastewater produced, the chemical method requires that the surroundings be carefully protected from the acids and reactive chemicals used to produce the reflective surface.
Several manufactured imitations can reproduce the colors and patterns of marble floors, but the beauty of natural marble is a result of its physical composition: calcite, which is a crystalline form of calcium carbonate (CaCO3) from metamorphosed limestone. Calcium carbonate crystals have a low level of light dispersal that allows light to penetrate the surface of the stone before being reflected back to the viewer. This gives the surface an appearance of depth and the reason that the ancient Greeks called the stone marmaros (shining stone). An accumulation of tiny, even microscopic, scratches on the surface of these crystals will disperse light at the surface instead of allowing it to reflect from the back of the crystals.
The traditional restoration method grinds and polishes the surface of the calcite smooth with successively finer and finer abrasives until the light entering the crystal is reflected off of the back of the crystal.
The chemical method, commonly called crystallization, relies on applying a very thin coating of a magnesium compound that is then heated by friction with steel wool pads to create small crystals of a magnesium compound in the surface scratches. A weak acid, such as Oxalic Acid, reacts with the calcium carbonate to make the carbonate available for reaction with the magnesium. The chemical solutions frequently include silica and fluoride in the magnesium compounds that create new fused compounds that handle light unlike the original, natural marble.
There is valid reasoning behind using magnesium compounds; many naturally occurring marbles contain a percentage of magnesium carbonate, although the stone is termed dolomite if the percentage of magnesium carbonate exceeds the percentage of calcium carbonate. The finest, white marbles are 98% and 99% calcite.
Crystallization produces a glossy surface of tiny, fused magnesium compounds on the surface of the marble. Although this is a smooth surface, it lies on the surface of the calcite and tends to reflect light instead of allowing it to penetrate to the back of the calcite. A few applications of the crystallization method will produce a high gloss without seeming to diminish the depth produced by the reflection of the calcite, but as successive applications of acids and magnesium compounds react with a greater percentage of the calcite crystals the surface appears to take on a plastic like surface gloss without the depth of light reflection characteristic of natural marble. Companies using the crystallization method tend to measure their results with a glossmeter, to measure the amount of reflected light, ignoring the difference between surface reflectivity and deep crystal reflection. To regain the original deep reflectivity of the natural marble, eliminate the plastic appearance, and repair the acid etched surface of the underlying calcite, the magnesium compound coating must be removed with traditional grinding and polishing methods.