By Mike Marsoun, Outer Island Stone Care

There are many ways to restore a marble surface that will make it look better, but the difference in appearance between “better” and “best” can be night and day.  
When these differences are explained it can be hard for the client to discern between fact and sales-pitch. In the course of my career I have had hundreds of meetings with clients to discuss options for marble restoration and more often than not, about half-way through the conversation I can see eyes glaze over, and I know I’ve lost them.  For some, it’s much easier when there’s adequate time to consider the information, and be prepared before discussing options. This piece is for them.
The two main choices when considering marble polishing are “re-honing”, and “compound buffing.”
This technique employs a marble polishing compound comprised of approximately 30% Oxalic Acid, a blend of oxide powders (tin oxide, aluminum oxide) shellac flakes, pH buffers, etc.  The compound is buffed over the floor with a typical 17” floor buffer (175rpm) with water to create a slurry, then vacuumed. The floor should then be cleaned with a diluted alkaline stone cleaner to remove compound residue, and return the surface to pH neutral. The result will remove most light etches and fine scratches.
Regarding effectiveness:  my “litmus test” for etch stains is that when scratching  the stain with your fingernail, if you get that chalkboard-screech sound that makes the hairs on your neck stand up, then the etch will still be noticeable after polishing.  Much improved, but still noticeable. If scratching does not produce the dreaded screech, then it will be removed completely.
With scratches, if you can feel them with the fingernail, it will be the same as above, improved but still there.  On most marble types, deep scratches, where there is actual crystal damage, will not be improved much at all.  Very fine scratches will be removed in most cases, again, depending on the type of marble.
 Compound buffing will improve any polished marble surface to some degree, but it will lack the colour and optical clarity of a full restoration involving diamond sanding.
Because this method is done in a wet slurry, with a slightly acid and abrasive compound, it will clean very well at the same time.  This process is the only way one can “acid clean” a marble surface, without ruining the finish.
The end result will leave you with a calcium-oxalate crystallized surface, of a deeper penetration level to what was produced in the factory; more calcium ions have now been supplanted by oxalate.
This is a chemical polishing process which is very easy to perform, therefore very popular with commercial cleaning firms.
To “re-crystallize” (technically a misnomer) a hexa-fluorosilicate acid fluid containing wax, is sprayed onto the surface and buffed with a jumbo steel wool floor pad.  This method is almost as effective as the compound polishing method mentioned above, but has a slightly different look, not as clear.
Drawbacks to this method is that it will change the chemistry from what was produced in the factory, to calcium-fluoride (a halogen derivative) and you will then need to remain with this process.  This process will also increase abrasion resistance, but the cost will be a loss of aesthetics. 
It is easy to recognize a floor maintained with this method, it will have a “plastic” look due to the waxes, and the grout will be discolored from the steel wool (carbon) and wax.  There will also be a yellow tint on white marbles as they will oxidize over time due to the reduced breathability of the stone. Note: this method should NEVER be used on white.  “Re-crystalization” is most effective when used with steel wool but the particles can impregnate the pores of some stones and the grout, causing various problems. 
Re-crystallization will also eliminate the ability to do light grinding restoration options because the diamonds (in most cases) will not get a “bite” and be able to consistently hone. In this case, a full restoration will be the only option, grinding off the surface crust created by the polishing, and exposing a new surface that will receive other treatments.
Diamond sanding is done to remove scratches and etching and re hone to a high degree.  Floors restored with this method, prior to compound polishing, can result in a better-than-new condition.
With grinding there are two options: resurfacing, and flattening.

Flattening will make all the tiles flat to one another and level with the grout joints.  This is the most beautiful option and should be considered as an upgrade to a typical marble floor, well worth the added expense.  These floors are much easier to maintain, and future re-honing costs will be lower.

Re-honing is a much lighter diamond sanding, usually starting 220 grit, but will still remove all the damage.  The tiles will still be slightly uneven, to the extent of the installation quality, but the edges will be slightly rolled over, or “cushioned” due to the sanding process.  The finish achieved with this process can be of the highest optical clarity and colour if done correctly.  

Regarding both grinding options it is important to note the degree of grinding that will take place.  Compound polishing can be achieved even if honing is ceased at 600 or even 400 grit diamond pads.  However, the finish will have much greater longevity if the grinding is taken up to 1800 or 3000 diamond pads. 
The reason is that the compound buffing needed to create a polish will be lighter because it will have to “close up” a much smaller scratch pattern.  If the polishing is less aggressive there will be less of an exchange of calcium-carbonate to calcium-oxalate which is weaker, there is less mineral breakdown needed to create the polish.
In this article the use of coatings of any kind are not listed as options. This is because coatings are not suitable options for most stone surfaces, particularly marble.
The use of coatings will not allow the stone to transmit water vapor, and the harsh chemicals used to periodically refinish these surfaces will cause deterioration through efflorescence, spalling, and sub-florescence.
The coat/refinish process is also very bad for the environment due to the VOC’s of the coatings, and toxic waste product created when stripping/refinishing.
Coatings also cause an immediate devaluation of the architectural asset, transforming it from a highly valued stone surface, to a high maintenance form of plastic, with the added loss of aesthetic value.
As you can see there are many ways to make a marble floor look “better,” but the effect could be short or long term based on the techniques used.  
Restoration costs can have a very wide price range and that can make choosing an option very difficult, especially in a corporate environment.  It’s not as simple as “cheapest price wins.”  Management personnel must be willing to make some hard decisions, sometimes choosing the more expensive option to save long term costs, realizing that what seems to be the cheapest option can actually be the most expensive option over time.  Restoration buying decisions should never be made on a one-time cost basis…that’s not how it works.   
Following responsible guidelines will certainly protect the longevity of marble surfaces, and education is key to making the right choice.