Decorative Concrete Resource Center

Decorative Concrete Bulletin #1

The Grinding/Polishing of Concrete

Grinding and polishing of concrete follows the same principle of refining Terrazzo to make it visually appealing. The tools and ancillary products used are specific to the concrete grind and polish industry. The process uses heavy duty polishing machines utilizing progressively finer grits of diamonds on diamond impregnated disks which grind down the surface to a desired degree of smoothness. Depending on the grinding procedure, and type of concrete composition (cement paste, fine aggregates, larger aggregates and deepness of the grind), the desired degree of shine is developed. Although there are some exceptions, almost any structurally sound old or new concrete can be polished.

*Advantages

In referring to the LEED rating system developed by the US Green Building Council, bare concrete floors could make contributions towards points as it can minimize the amount of materials needed to complete the project, thus lowering impacts. Also problems associated with moisture vapor transmission can be reduced or eliminated with less material costs involved. Both old and new concrete can be polished to provide a smooth glossy surface that is easy to clean and maintain. The process does not incorporate high odor products and has significantly less environmental impact than conventional solvent based coatings.

*Ancillary Products

Chemical hardeners or concrete densifiers are used to densify the concrete. Densifiers react with chemicals used in concrete such as calcium hydroxide to produce silicate hydrates, which in turn fills in voids and densifies. This allows for a smoother surface and deeper shine as well as providing better surface abrasion resistance. Although there are many types of densifiers, they all function in the same manner and the type used is more of an individual preference based on each individual’s polishing techniques. Numerous  manufactures make a  myriad of densifier types to provide a broad based platform from which to choose. Nonetheless, even after the concrete is densified, some voids are still present. In this regard, many companies offer a Concrete Conditioner and stain guard product comprised of a ultra small particle self crosslinking hydrophibic polymer that can be used to increase long term performance, gloss and stain resistance.

Helpful tips and demystifying the myth’s associated with the industry.

*Densifiers do increase concrete density and provide for performance improvements.

*All grind and polish equipment is different and can provide for varying results based on the number of polishing steps utilized as well as the actual diamond grit size used. Factors such as weight of equipment, workmanship and concrete composition are variables affecting final results.

*Although polished concrete requires less maintenance, the shine doesn’t last forever. Polished concrete can be scratched and be de-glossed from foot traffic over time.

*Proper routine maintenance can extend the longevity and performance of the shine.

*Not all concrete is created equal and the results, even when polishing is performed the same, do not always create the same look and shine. Some concrete is more porous than other concrete while some concrete is softer than other concrete. The concrete in the north utilizes aggregates and materials available in that area while concrete in the south utilizes ingredients available from that region. In the lower southern States, softer aggregate are sometimes utilized because they are predominant in that area. These variations of concrete as well as how they were installed and finished can be a factor on finished polish appearance as well as how well the shine stands up to various types of traffic.

*When a floor begins to lose its shine from long term use, the shine can normally and easily be rejuvenated utilizing the final polishing process step without the need to re-densify the concrete. To maintain shine, a maintenance provision can be employed on a yearly or biennial basis to re-polish the concrete surface in heavier traffic facilities.

*Keeping the concrete clean, will increase the longevity of the shine. Dirt particles and other foreign contaminants act as an abrasive (much like sandpaper) when attached to shoes or walked on. This can decrease the shine and smoothness.

*Concerning stain resistance, the quicker a spill can be cleaned up, the less there is for a chance of developing a stain. Some chemicals or spills will not immediately stain the concrete, but if left on the concrete for many hours, the spill may leave a stain that cannot be removed by normal cleaning techniques. Stain guard products can help in reducing staining, but there is no substitute for good housekeeping.