So your marble is dull, scratched and in major need of help! Out come the Yellow Pages; you call several marble refinishers and set up a few appointments. How hard can it be? You’ll get a few estimates, check some references and select a professional to do the job. And then the fun begins. The first professional tells you that your floor needs to be ground flat in order to be fixed properly. The second professional tells you he can hone and polish it—no grinding required. The third professional tells you he only needs to recrystallize the marble to make it look like new. Now that you’re totally confused, how do you determine who’s right? What’s the difference between grinding and honing? What are polishing and “recrystallization?” This section will arm you with enough knowledge of these terms to help you ask the right questions & help you make an informed decision. Once you are familiar with the processes used to restore marble and stone, you will be better equipped to safe guard the investment of your natural stone.
WHY DOES STONE SHINE?
When stone becomes dull and scratched, it obviously loses its shine and luster. At this time the stone needs to be refinished and polished to restore the shine it had originally. Why does stone shine, and how can a lost shine be recovered? All stone is taken from the earth in the form of raw blocks. Explosives, large saws and specialized equipment are used to extract the stone from the earth. The stone blocks are then cut into thinner, more easily handled pieces called slabs. The slab itself is then processed, depending on the intended use of the stone. It may be given a high shine and shipped to a stone fabricator, who will ultimately turn it into a table, vanity top, counter top or whatever; or it may be transformed by some very expensive and sophisticated equipment into tiles for installation on floors or walls. The deep shine we see on polished stone is achieved by rubbing the stone with a series of abrasive materials. The process is very similar to sanding a piece of wood. The stone is rubbed with a coarse abrasive grit, followed by finer and finer grits until the stone becomes smooth. The scratches left behind from one grit; are removed by the next, creating finer and finer scratches. The process continues until the scratches are microscopic. The shine on the stone is achieved by abrading the surface to the point at which it becomes extremely smooth and starts to develop some reflectivity. The shine on the stone is thus a product of optics. This same optical property can be observed on a pond. When the wind is blowing and the surface of the pond is wavy, it becomes difficult to see a reflection; when the air is still and the pond is calm, a deep reflection can be observed. So in order to achieve a deep shine on your stone, all which really needs to be done is to smooth it until it shines. Sounds simple enough, doesn’t it? Unfortunately, the techniques employed to achieve this degree of smoothness require special knowledge and training. This is not friendly territory for the do-it-yourselfer. To help clear up the confusion, let’s define some terms used in the business, then you will be able move on to the all-important issue of selecting a stone care professional.
Grinding is the process by which the surface is aggressively sanded to remove large stocks of the stone. This process is usually recommended when stone tiles are uneven (lippage) or when there is very heavy scratching left from wear.
Lippage is the term given to uneven tiles that are set higher than one another. Grinding is recommended when the lippage exceeds 1/8 inch or if one desires to have a completely flat floor.
FLATTENING / MONOLITHIC
There are some very good reasons for grinding a stone floor flat. A flat floor is easier to maintain; since there will be no lips where dirt can accumulate. The grinding process, if performed correctly, will also eliminate depressed grout joints—the grout will be even with the tile’s surface so that dirt and grime can’t accumulate. A completely flat floor eliminates all unevenness, giving the floor the illusion of being monolithic (one piece). Note: a stone floor does not necessarily have to be ground to remove scratching. A skilled craftsman can repair it without grinding, yet a ground floor does yield a better appearance & is easer for you to maintain. Just as there are several good reasons for grinding, there are also some disadvantages. Grinding is very time-consuming and expensive; with some hard stones, like granite, it can take an entire day to grind 50 square feet. The grinding process can be very messy if not done correctly. Copious amounts of water are needed to grind a stone floor; producing a heavy slurry of stone and water. If adjacent areas such carpet, wallpaper, baseboards, etc., are not protected properly, water damage may occur. Before deciding on grinding, all the above considerations must be carefully weighed. Discuss the options with your stone care specialist.
Honing is the process of smoothing the stone with the use of abrasives. Although not as aggressive as grinding, it does require the use of water, and can also be quite messy. Honing is performed to remove scratches, and will not remove lippage (uneven tiles). It can, however, round the edges of the stone, giving a smoother finish or “Pillowed Look” to the edge. The honing process is usually achieved with the use of diamond abrasives, although some contractors prefer silicon-carbide bricks or screens. Which abrasive is used is not as important as the skill level of the craftsmen. Honing can leave a stone floor with very little shine, although some stones will acquire a satin-like luster at very high hones. You may hear the contractor talk about grit sizes when discussing the honing-and-grinding process. The following table will serve as a guide to grit sizes. The lower the number, the more aggressive the grit. Generally, grinding is what takes place using any grit of 60 or below; honing begins at 120 and proceeds upwards. A skilled craftsman could stop at a 400 or 600 on marble before powder polishing but the higher they go with the diamonds; the longer the shine will last. The higher they go with the diamonds, the tighter they will be able to get the pours of the stone. The tighter the stone is, the more durable it will be. With granite, it is usually necessary to proceed through to the highest grit. Some craftsmen may choose to polish with diamond abrasives to the highest grit, producing a very high polish, while others may choose to switch from a diamond to a powdered abrasive (see next section). Whichever method is chosen, the final result is what counts. The following table lists some of the most common grit sizes used in the stone industry. The lower the number, the more aggressive the grit.
As previously discussed, the high shine observed on stone is the result of smoothing it with fine abrasives. Most craftsmen will use diamond abrasives to hone & polish the stone, and then switch to a powdered abrasive to achieve the final polish. Powdered abrasives contain superfine crystals of aluminum oxide or tin oxide. These powders are usually white, but can be yellow, brown gray or black. The abrasive powder is worked into the stone with a weighted floor machine (buffer) using water and cloth or natural hair and/or polyester fiber pads. The powder is worked into a slurry until a polish is achieved. The craftsman removes the slurry with a wet-vac or mop and rinses the floor to remove excess powder. It’s a relatively simple procedure, but it requires a good deal of practice for several reasons. Many polishing powders contain a compound known as oxalic acid, which is used to speed the polishing process, and if too much powder is used, the stone can burn. A burned floor has a characteristic dimpled appearance; the stone will have what you might consider a molten, plastic shine. This burned appearance is commonly called “orange peel,” for reasons that are obvious when you see it. If the craftsmen orange-peels the floor, he will have to re-hone the floor to remove it. On the other hand, if too little powder is used, the final polish may not be achieved. A good craftsman will be familiar with the powder polishing technique.
Restoration is required when the surface of the stone has been so badly worn that it has deep & very visible scratches. As a point of reference, common beach sand normally will cause a scratch that is just slightly finer than the scratch pattern of a 220 Grit diamond. So, if the surface in question has that kind of wear, than it will require starting at that grit of diamond and proceeding up through different grits until the desired appearance is reached. If a you have your natural stone properly maintained than you should rarely if ever need to have it restored a second time, unless there has been some type of damage done to it.
MAINTENANCE – Natural Stone and Tile
In most cases, maintenance will consist of doing a detailed cleaning of the stone. Once it has been properly cleaned, your stone care professional will be able see if they need to do some light diamond work in the high traffic areas, but in most cases they should only need to powder polish it too bring back its natural beauty. Proper maintenance is key, when it comes to the appearance of your stone. Much can be done by you on a daily basis to reduce the cost of maintaining your natural stone surfaces. Regular/daily removal of sand & grit is the first line of defense. This is best done by using a vacuum with a soft head designed for hard surfaces. You can reduce the amount of sand & grit even more by having rugs / walk off mats at all entry doors. Regular cleaning should be done with a high quality mop and proper stone soap. A very important point when it comes to mopping stone floors is this, make certain that your mop is wrong out as dry as you can get it. If you use a very wet mop, you will just be pushing that dirt around the floor, into corners, grout lines, the pours and along base boards. Most stone care professionals will gladly assist you in developing what to use and how to do
GRIT SIZE TABLE
Rough or Coarse Grinding: (Generally Used for Coating Removal, i.e. paint, urethane, epoxy, etc)
16 Grit or Lower
Grinding: (Used for Heavy Material Removal, i.e. Flattening, Lippage & Heavy Scratch Removal)
24, 36, 60
Honing: (Can Be Used for a Softer Final Appearance)
120, 220, 400
Polishing: (Used for a High Shine Final Appearance)
600, 800, 1,800, 2,000, 3,000, 3,500
Ultra High Diamond Polishing: (Not Recommended for Flooring Surfaces – Unless it is a Granite Floor)
Very last step of the polishing process, using special powders with very fine abrasives and other ingredients. Powder polishing can be used as the last step in either a honed or high shine final appearance.