Basic Guidelines for “Two-Step” Restoration Procedure of Marble Shower Stalls (Part 2)
Honing and Polishing of Marble Shower Stalls
The definition of marble makes reference to calcite- based stone that are traded as marble. Stones that are still traded as marble, but are not calcite- based (serpentine, ophicalcite, etc.) are not part of this group. Dolomitic marbles can be part of this group, providing that the final polishing is going to be made “hotter” than average.
1st Step - Honing
The use of good-quality dry diamond honing pad with 4” diameter on a flexible backer pad is highly recommended. The logic behind this recommendation is that by working dry, it is possible to assess immediately the progress of the work, and there will be less mess to clean after the job is finished. Sure, dust will be produced, especially when using low grits (metal-bond or resin-bond), but if the RPMs of the right-angle grinder/polisher are kept at the lowest level (600 RPM- or less, by further controlling the speed with your fingertip on the trigger), most of it will fall on the floor instead of flying around. Appropriate dust-masks should be worn at all times to avoid the very light dust that could find its way in the operator’s respiratory tract.
There is no way to pre-determine which grit you should start with. It could be just a light honing with, say 400 grit and then polish. There is also the possibility that in many cases- depending on the stone and the polishing compound that you have available- you could get away with just polishing. At the other end of the spectrum of possibilities, the situation may require you to start with a 50 grit resin-bond or, in the most severe situations, even a 60 grit metal-bond (electroplated) pad. It is usually possible to polish after 400 grit (800 or 1500) before polishing.The same principle of keeping the polishing slurry “hotter” on floors made of these types of marbles, applies in the case of a shower enclosure as well. Some very delicate marbles (Botticino, for instance) will need to be brought up to 1500/1800 grit before polishing, but the compound must be kept “lukewarm” or else they will “burn”. Always test first starting from the least aggressive option.
2nd Step - Polishing
Although dry-polishing gives you a definite edge (most of the time) over wet-polishing when polishing floors, it is understandable that certain contractors may prefer wet-polishing. After all, dry-polishing must be “understood” to be appreciated. In the case of a shower stall however, wet-polishing is not advised. Think of this: wet-polishing is very time consuming and it creates a huge mess that will take a considerable amount of time to clean up. Every finished section will need to be properly masked or the splatters generated while polishing the previous section will etch it, thus requiring further repair. None of that will be necessary when using the dry-polishing technique (which requires specifically designed polishing powders). And the clean-up at the end of the job will be a fraction.
But while the dry-polishing of a horizontal surface requires that you position some powder on the surface of the stone and then, after slightly wetting it, you place the polishing pad attached to your variable-speed right-angle grinder/polisher on top of the wet powder, you certainly can’t follow that procedure on a vertical surface. So, this is what to do to polish a wall:
Prepare to dry-polish with a white nylon pad (or other appropriate polishing pad) on the 4” or 7” backer-pad attached to your variable-speed right-angle grinder/polisher. Spray a little mist of water on the pad to make it evenly damp (not another one), sprinkle some appropriate dry-polishing powder on it, tap it with your fingertips for proper bonding. Spray a quick squirt of water over a couple of tiles starting from the highest row of tiles to be treated, and then proceed from wet to dry trying to avoid splattering (by controlling the RPM with your fingertip on the trigger), and working no more than 2 to 3 square feet at a time. The first set of tiles to be polished may have to be done twice because the pad does not have any previous build-up of polishing compound. As you proceed with the work and the build-up on the pad increases, the need for fresh powder on each section will decrease.
As indicated before, it is not advisable to do more than two or three tiles at a time, on average. Trying to do more could involve using more powder and more water, which in turn could produce active pH spattering that you don’t want. In other words, the perceived saving of time, will most likely turn out requiring more time instead. However, with certain “fast” marbles (like Botticino) you may be able to target up to four five tiles each section because the quantity of powder and water necessary to polish an average marble will be more than enough to double the productivity with those kinds of “fast” marbles.
Constantly remember that with dry-polishing, you are controlling the “heat” of the powder by increasing or decreasing its quantity or the quantity of the water (or both) based upon the requirements of the marble at hand.
End of Part 2
For more detailed information and step by step instruction, purchase our Natural Stone Maintenance Book or consider attending one of our Stone Restoration Training Classes in Wilson, NC.