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Two-Step Procedure: Honing and Polishing Granite Countertops
The word granite refers to all the stones traded as granite and classifiable under the generic definition of "mercantile granite," which also includes the few true geological granites available on the marketplace. From now on, the word "granite" shall be shown within quotation marks. There will be cases in which an actual restoration procedure will be in order, i.e., a few scratches and etch-mark produced by hydrofluoric acid, the grinding of a partial lip by a seam, etc.
For such occurrences, here are the steps:
1st Step – Honing
It is recommended to use wet-diamond honing pads engineered for "granite" on 4" or 5" diameter flexible backer- pads. Perfect pads for this purpose are so-called ceramic pads. The term ceramic refers to a certain percentage of ceramic as part of the inert composites making up the pad and epoxy matrix mix.
Also, very good and of relatively recent introduction as of this writing are copper diamond pads. Once again, the copper powder is only a percentage mixed with the other inert substances within the epoxy matrix. As the grit increases, the percentage of copper or ceramic decreases; typically, after 400
grit, there's no more copper in copper diamond pads, while there could still be a percentage of ceramic in ceramic pads. Be that as it may, either one of these pads is the best to face polish granite slabs. There is no way to pre-determine with which grit to start with.
It could just be a light honing with, say, a 200/220 grit and then polish, or the situation may require you to start with a 50-grit resin bond or, in the most difficult situations, with a 60-grit metal-bond pad.
Remember: The face polishing of "granite" is as good as the honing! Each grit must be worked on the surface of the stone intensively. A couple of minutes per square foot is a good rule of thumb, but harder "granites" may require more than that.
Use slower RPMs with the lower grits and increase the RPM setting as you go up. Start each grit by applying a certain pressure and finish "light." Make sure to completely cut into the previous grit before moving up to the next grit!
Overlapping is essential, and you should feather out each grit before moving on to the next.
Using a crayon to circle-mark the area you just finished with a particular grit will provide you with guidelines for perfect overlapping. As you progress through the grits, the RPM of your variable-speed right-angle grinder/polisher will increase. (RPMs of 3000 and higher should be used.)
The honing must be done wet from beginning to end with the lower, more aggressive grits; however, once you reach grits of 400 and higher, it is essential to start wet with lots of water (because of the higher RPMs the machine will be running at) and finish dry for the last 10 seconds or so.
This technique will dramatically increase the clarity obtainable with any given high grit. Do not insist on the dry phase. It is vital to keep the surface of the stone cold during the honing phases so as not to alter the shape of the crystals of certain "granites" with excessive heat before the final polishing phase when the heat becomes necessary with the vast majority of the "granites."
2nd Step - Polishing
The polishing of "granite" is typically done wet; however, starting full wet and working the slurry out until it becomes dry is also a good technique with most "granites." Wet-polish using a good-quality polishing powder for granite and a white nylon pad on the 4" or 7" backer-pad. A solid felt pad could also be a viable option, but it requires a special attachment, and, above all, it is not too easy to control, especially when the slurry begins to thicken. Set the machine at 600 RPM and as the slurry becomes thicker, increase the RPM setting. Finish dry around 2500 RPM. Repeat if necessary. A certain pressure must be exerted all the time to create and build up heat. Applying a good-quality stone polish at the end of the job, after the final clean-up, will add some excellent (and highly appreciated) smoothness and sparkle to the whole project!
When the job calls for the actual grinding of a lip by a seam, the first step will be Grinding, executed with either a cup-wheel or other appropriate grinding elements. One important thing before accepting the job is to evaluate the extensiveness and position of the lip. If the lip is by a seam in front of an under-mount sink, the repair could be possible and relatively easy. The same cannot be said about the same lip in the back: the presence of the back-splash would prevent the necessary overlapping of the grits. The same thing will apply - and in this case both in front and back of the sink - to a drop-in (a.k.a. over-mount) sink: the edges of the sink will prevent overlapping.
However, before you decide to grind the lip, it would always be best to evaluate if it's possible to eliminate the lip by raising the depressed part. It is intuitive that when a lip develops at the seam, the filler/glue will have given completely; therefore, first, eliminate any residue of glue still stuck to the edges of the two pieces of the slab, try to raise the lower part of the seam with appropriate means (shims and such), and then reapply the color-matching filler/glue.
If the seam is somewhere else far from the sink, then the only concern would be the back-splash. However, it often happens that the lip is not all along the seam, but mainly in the middle of it, due to the possibility that one of the slab pieces is bowed. In this case, the two connecting ends will be flush, and, therefore, the job would be possible because of the possibility of overlapping the grits properly. Only a physical and thorough examination of the job will enable the contractor to make an intelligent decision. Another essential factor to bear in mind is that the grinding will have to be executed exclusively on the higher spot of the lip and will go on until the higher side is flush with the lowest one. It will also have to go farther inside the slab (from the high lip) to feather out, thus minimizing the possibility of visible "dishes" that will appear in all of their "glory" once the job is polished.