Repair & Restoration
Early in the 1980s the use of diamond- tipped saws and high-technology quarrying methods once again made marble and granite an affordable and prestigious building material in the United States. With its renewed popularity, however, a new set of problems has developed for building owners, managers, architects, and janitorial service companies. Proper maintenance and restoration of these materials became imperative.
New Methods Were Needed
The first approach was to perform the same maintenance as had been performed for years on vinyl asbestos tile floors by applying floor finishes. As was discovered, the application of floor finish alone was not harmful to stone but when these finishes had to be stripped. The use of the highly-caustic strippers and highly-abrasive stripping pads commonly used on vinyl asbestos removed the high-polish finish that was used on many of these stones. (Honed surfaces have proved to be somewhat easier to maintain than highly-polished stone surfaces.)
High-polish stone floors were soon found to need a different, specialized method of maintenance and, at times restoration. Today there seems to be an endless number of methods to care for highly-polished stone including crystallization and oxalic acid buffing to name just two. All of these, however, are basically maintenance procedures and while applying them to new surfaces can yield excellent results, they will not work as methods of restoration.
In this article, we’ll focus on restoring, as opposed to maintaining, a stone surface. There are three methods that are most commonly used in the restoration of a high polished stone which has lost its natural finish. Each is very similar in concept but very different in materials used, results, cost, and time.
Once the stone has lost its quarry polish there is only one means of restoration, and that is grinding the stone. Stone grinding, the oldest of all of the modern methods of restoration, was originally designed for grind-in-place thick dimensional stone. The grinding machine uses stones to repolish floors.
The most-used grinding stones range from 24-grit to 1000-grit and should be used progressively in a minimum of six steps in the restoration process. After grinding and mechanical polishing is completed, the stone must be polished again with either chemicals, metallic elements, or buffing compounds.
The type of stone (granite, marble, or travertine), combined with chemical make-up and the hardness of the stone, affects the selection of the final buffing product. If your stone has not been installed to a relatively lip-free state, (meaning that the stone should not protrude more than the thickness of a dime) this method will generally produce the smoothest, most lip-free surface of all of the methods.
However, there are certain drawbacks to this method. Before attempting to use this method, you should make an inspection to make sure that this method is appropriate. Here’s what you should do in the inspection:
- Make sure that the flooring was installed with no subsurface hollow spots in the setting material.
- Check to see that all blocks are firmly set and free of movement.
- Determine the thickness of the stone to make sure that it’s at least one inch thick.
If the floor doesn’t measure up in any of these areas these defects could allow for cracking and breakage of the stone during the restoration process because the 250-pound grinder that you’ll need to use can bounce dramatically while it’s being used. Additionally, thick dimensional stone (one inch or better) is better suited for this type of restoration.
Production rates for this labor-intensive procedure can be as low as 25 square feet per day up to 100 square feet per day. Your average cost can range from approximately $6.00 to $15.00 per square foot depending upon:
- The type of material needing restoration
- The need for regrouting or repair of grounding
- The amount of wall edges
- Initial damage to stone material
- Individual complications
- Geographic location
- The need for unionized labor
As the new technology for quarrying stone developed, so did this method of polishing and restoring the stone. Its principles are the same as stone grinding except for the use of diamond abrasives instead of stone. Diamond abrasives, which have a much longer life than other conventional abrasives, are fixed to some type of flexible support material with a bonding agent such as nickel and resin.
Unlike stones and screens, diamonds come in hand pads, belt disks, and flat sheets, and are able to be used on many labor-saving machines. These diamond abrasives range from 60 to 3500 grit in the most popular textures. Along with stones and screens, they must be used progressively in order to get a smooth, highly- reflective finish.
Diamond grinding at this time, unfortunately, does not remove lippage as well as stone grinding. However, diamond grinding will produce a finish just as highly reflective as stone grinding.
The diamond grinding machines generally weigh from 20 to 200 pounds and run much smoother than a stone grinder, without the bounce. Their lighter weight and smoother operation, in turn, make them much safer on stone that has not been set properly. They also have developed a reputation of not breaking stone material during the restoration process, even when used on the new, 3/8-inch marble tiles.
Diamond grinding, as with stone grinding, requires a final polishing with chemicals, metallic elements, or buffing compounds. Production rates are from 100 to 500 square feet of restored material per day at an average cost of $3.00 to $8.00 per square foot, depending upon the same variables as previously listed under stone grinding.
Restoring Marble and Granite Floors
Silicone Carbide Grinding
In theory, this is the same as the other methods of restoration. It also comes in progressive textures from 60 to 1000 grit, and they, too, must be used progressively to obtain the best-possible finish. However, the ability to remove scratches and to restore stone to a high polish is limited, and removal of lippage is virtually nonexistent.
Where cost and speed is of main concern, however, this method does offer a viable option. With production rates of 500 to 1000 square feet per day and a cost of $3.00 to $5.00 per square foot, this is an economic, moderately effective means of restoration.
As with stone and diamond grinding, the stone must be finished with chemicals, buffing compounds, or metallic elements. Unlike stone and diamond grinding, however, the screen disks do not produce satisfactory results on granites, but only on marbles, travertines, and terrazzo.
Choosing the Most-Appropriate Method
Damaged stone must be ground by some method to remove the damage and give the stone the clarity and sharpness our customers expect.
When a stone floor has been restored it should be treated with some method to help prevent staining, add slip resistance, and provide a maintainable surface. There are many products and treatments available. However, some are much better than others.
Conventional floor finishes, for example, should not be used. Any product that requires stripping or the use of harsh chemicals or strip pads for removal will remove the polished surface and cause scratches that will in turn bring about a need for more frequent restoration.
As a building service contractor offering stone care, it goes without saying that you should know the stone used in any particular situation. In addition, you should do an on-site inspection and provide your client with a full package which includes analysis of the situation, a list of methods and products needed for the restoration, and a complete explanation of the maintenance procedure that you propose to use.
Whatever brand of final finish you choose, you should be sure of the track record of the manufacturer, especially when choosing a maintenance product. Their knowledge of stone, the availability of products and materials, and the manufacturer’s quality control should be taken into serious consideration.
The use of bath tub chemicals or the use of an unproven restoration procedure can turn out to be very costly in the long run.
In closing, I should point out that highly-polished stone floors are expensive to quarry, purchase, and install, and restoration and proper maintenance are also expensive when performed correctly. However, once you’ve chosen and performed the proper method of restoration, a highly-polished stone floor can become very economical and easy to maintain, while returning your customer’s stone floor to the level of appearance that they selected when the material was first chosen for use in their building.
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