There seems to be endless methods to care for highly polished stone. One of these endless methods is grinding. There are actually three main methods of grinding: grinding with stone abrasives, diamond, or silicone carbide disk. Each is similar in concept but very different in materials used, results, costs, and time.

Grinding with Stone

Stone grinding, the oldest of all the modern methods of restoration, was originally used for ground-in-place, thick dimensional stone of l-inch (2.5 cm) or more. The grinding machine, commonly known as the Achille Grinder (made in Italy), uses stones ranging from 60 to 1800 grit, which should be used progressively in at least six steps in this restoration process.

If lippage is present (pieces of stone protrude more than the thickness of a dime) this method above all others will generally produce the most lip-free surface.

After grinding and mechanical polishing is complete, the stone is normally polished again with either chemicals, metallic elements, or buffing compounds. The type of stone – whether granite, marble, or travertine – its chemical composition and hardness determine the selection of the final buffing product used.

There can be certain drawbacks to using this method. An inspection prior to restoration should be made to determine that the flooring was originally installed with no hollow spots in the setting material below the surface and with all the tiles firmly set and free of movement. These two defects could cause cracking and break- age of the stone during restoration, because the 250-pound (113.4 kg) grinder can bounce dramatically while in operation.

Production rates are normally 100 to175 square feet (9.3 to 16.3 sq.m) per day. Average costs will vary from $5 to $8 per square foot depending upon

• the type of material
• the need for regrouting or repair grouting
• the amount of wall edges
• initial damage to stone material
• individual complications
• geographical location

Diamond Grinding

As diamond technology developed for quarrying stone, so did this method of polishing and restoring stone. Its principles are the same as stone grinding except instead of using stones it uses diamond abrasives. Diamond abrasives last much longer than other conventional abrasives. The diamonds are affixed to some type of flexible support material with a bonding agent such as resin or nickel. Unlike stones and screens, diamonds are available in the form of hand pads, belt disks, and flat sheets, so they can be used on many labor-saving machines. Diamond abrasives range from 60 to 3500 grit in the more popular textures. Like stones or screens, they must be used progressively in order to get a smooth, highly reflective finish. Diamond grinding at this time does not remove lippage as well as stone grinding. However, diamond grinding will produce a surface which is as highly reflective as stone grinding.

The diamond grinding machine generally weighs 120 to 180 pounds (54 to 82 kg) and runs much more smoothly and without the bounce of a stone abrasive grinder. Lighter weight and smoother operation in turn make them much safer on stone that has not been set properly. They have not been known to break stone material in the restoration process. Like grinding requires a fine polishing with chemicals, metallic elements, or buffing compounds work o produce the final finished surface. Production rates are 250 to 500 square feet (23 to 46 sq.m) of restored material per day, at an average cost of $3.50 to $5.00 per square foot, depending on the variable listed above.

Silicone Carbide Grinding

In theory, silicone carbide is same as stone abrasive and diamond grinding. It also comes in progressive textures from 60 to 1000 grit. It must be used progressively to obtain the best finish possible. However, its ability to remove scratches and restore the stone to a high polish is limited, Removal of lippage is virtually non- existent. Where cost and speed are main concerns, it does offer a viable option. With production rates of 500 to 1000 square feet (46 to 93 sq.m) per- day and a cost of $2.00 to $3.00 p square foot, this is an economical moderately effective means of restoration.

As with the other two methods, the stone must be finished with chemicals, buffing compounds, or metallic elements. Unlike stone and diamond grinding, the screen disks do not produce satisfactory results on granites. only on marbles and travertines. In order to return stone to the clarity and sharpness desired, the damaged stone must be ground using one of these grinding methods.

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