TECHNIQUE AND THE CONCRETE POLISHING PROCESS
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 Bevel-Kut™). 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 grinding technique, such as on a surface that is causing excessive heat, or glazing 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.
Determinations made in planning and extra time taken in flattening the floor in the early stages of the process will make each stage easier and increase the probability of a successful result. It is equally important to complete each grit of the grinding process. Do not skip any steps in the process. Once again, much haste, less speed.
The standard rule for shifting from metal (grinding) to resin (polishing) bonds is to restart the grit process one step lower than the last metal grit used. Look at your arsenal of tools: if you finish with an 80 grit metal and have a 50 and a 100 grit resin bond in your tool set, start your polishing sequence with the 50 resin, not the 100.
Speed and weight are also incremental factors in the grinding and polishing processes. If you have an uneven floor, you might want to add weight to your machine, particularly if you have a lighter model. Always start with a slower rpm when working in the metals and increase your speed with each subsequent stage, as you observe it is needed and remove any added weights. Your final stages of polishing will be done in the upper end of your machine's speed, as will any burnishing you do afterward.
The end result of the concrete polishing process is a durable surface that will last a long time with minimal maintenance and can be brought back to its original sheen with burnishing, or by touching up with the highest polishing grit used in the original process. The concrete polishing process is also an ideal process for use in Leed Certified construction as it renders, raw concrete, or recycles an old concrete floor into a finished product. Regardless of your job requirement, the concrete polishing process yields a beautiful, highly reflective, durable and cost effective solution for a finished floor.
We encourage you to explore the many design publications, websites and blogs that are available on the subject of concrete design. There is much to learn and we at Kut-Rite are committed to a continued improvement in the information we make available to the concrete polishing and surface preparation industry.
