Substances high in acidity such as orange juice, vinegar, wine, beer, tomato products, mustard, carbonated beverages, ink and salad dressings, as well as soaps excessively high in alkaline, will “etch” (or dull) the finish on most unsealed natural stones and terrazzo. Etch marks result from damage to the stone or terrazzo’s finish. In order to properly understand etch marks, you should understand “technically” a little bit about what causes a marble to shine and appear polished. A polished finish results from grinding the surface, typically with silicon carbide or diamond abrasives, that are made of very small or “fine” pieces of natural diamond. At the quarry, the factory uses finer and finer (sanding) abrasives until the pores on the stone’s surface are virtually closed. When the pores are closed, light cannot be absorbed into the surface of the atone. Thus, light reflects easily from the stone’s surface making the marble appear shiny or polished. When an acid comes in contact with the marble, the acid chemically reacts with the calcium carbonate in the marble. This ”attack” on the stone’s finish re-opens the pores on a polished stone. Light is no longer able to reflect off of the stone’s surface resulting in a “dull” mark or spot.
Minor etch marks can usually be “hidden” (or covered) with one or more coats of a high-gloss sealer temporarily filling the open pores in the stone which will usually restore the shine to the surface. Keep in mind that once sealers are applied, they will typically need to be maintained. The frequency of re-application will vary depending upon foot traffic. Severe etch marks may be repolished with diamond sanding equipment If there are more than a few etch marks which need to be repolished, you may want to contact a restoration contractor who will have experience in marble polishing and have the correct equipment available. However, if the job is small, hand-held diamond sanding pads are relatively easy to use and can restore the stone’s natural shine without using high-gloss sealers. Natural stone distributors should have more information about where this type of equipment can be purchased.