What is Concrete Polishing?

This following excerpt is taken from Kut-Rite website and I think explains the whole process rather well:

The concrete polishing process removes materials by employing the use of a diamond grit, set in either a matrix of sintered metal for the removal (grinding) process, or in a resin matrix, for the polishing process. The diamond grit used becomes incrementally finer by changing to progressively finer tools, until the desired finish is attained.

The metal bond tools, which are used in the "grinding" phase of the process, consist of sintered metal/diamond matrix blocks molded or brazed on either round or trapezoidal plates and whose shape is designed to aggressively cut and flatten the normally uneven surface of raw concrete. This stage of processing is referred to as the grinding stage. A set of grinding tools typically consists of 25, 40, 80 and 150 grits (Kut-Rite also offers a fast cutting three step 30, 70 and 140 grit combination, called the BevelKut™). The hardness of the "diamond bond" needed for the job is determined by the hardness of the aggregate used in the concrete. A harder bond diamond might be needed with softer aggregate to avoid tool burn out and premature wear, otherwise a standard bond is almost always adequate. During the grinding process, in addition to flattening and removing undesirable residue from the floor surface, a properly used tool will establish a pattern of scratches that in the final stages of the process will produce a consistent reflective quality that satisfies, or surpasses our visual and aesthetic expectation for a finished floor.

Resin bond tools are used in the polishing stage of the process. A full set of polishing tools will consist of increments that approximate 50, 100, 200, 400, 800, 1500 and 3000 grits.

In some circumstances, it is advantageous to use a wet grindingtechnique, such as on a surface that is causing excessive heat, orglazing over of the diamond surface. Wet grinding is sometimes a preferred method for environmentally sensitive job sites, to eliminate dust. Water is introduced to the concrete surface either manually by crew, or by a tank mounted on the grinder/polisher. Wet grinding is more labor intensive, due to the cleanup requirement of the slurry generated by the process.

Depending on the character and quality of the concrete, a "densifier" can be added to harden the surface of the floor. Densifiers are liquefied compounds of silicate, normally sodium or lithium. The silicate compound reacts with the calcium that is always present in the concrete and forms a hard layer, which can be polished to a minimally porous, high luster that will remain stable over time and use. The concrete can also be stained with color and designs, or sealed at the point of processing that the porosity of the floor warrants.

Taking the time for planning and analysis is by far the most critical step for a successful grind: taking the important time to walk around, look, observe hardness, porosity, uniformity, flatness, any coatings, glues, cracks, or imbedded materials that need to be addressed and plan the approach you will take, beginning with your first grinding step. Should you do a "cream" (topical) polish, or do you want to grind the floor deep enough to expose the aggregate. Scarifier tools, or polycrystalline diamonds (PCDs) might need to be used to remove any coatings, residues or mastics. The time you take to plan will affect every subsequent step and determine if any costly or time-consuming measures might need to be taken because of poor planning.