ForConstructionPros.com

Polished concrete is the highest category of steps of processed concrete. Any grit abrasive from approximately an 800-grit resin and above, typically to a 1,500 or 3,000 grit, is considered a polishing step. A polished concrete surface has clarity of reflection like a mirror and has a glass-like finish.

The variables
The process of grinding, honing and polishing concrete is more technical than most realize. There are many pre-existing variables that can affect the end results of the process performed. Some of these variables are within the contractor's control, such as the quality of your equipment and abrasives and the motion and speed at which you operate your equipment. Others are beyond a contractor's control, such as levelness and flatness of the floor or the concrete mix design used. Knowing how to contend with these variables is the difference between a craftsman who is detailed and results-oriented and a contractor who simply goes through the motions.

One of the main variables on a polishing job is the concrete itself. Residential concrete is generally a low PSI concrete mix (2,500 psi and under) that has been hand troweled. Lower PSI concrete does not polish as well because the surface is not as dense and hand troweling leaves the surface with lots of highs and lows. On the other hand, commercial concrete is a higher PSI concrete mix (3,500 psi and up) that is machine troweled in the open areas and hand troweled in the corners and tight areas. Higher PSI concrete polishes better because it is denser and the surface does not have many highs and lows.

If you know a slab will be polished before it is poured, whether in a residential or commercial setting, suggest a polishing-friendly mix design and floor flatness rating to the general contractor or owner. The customer will in turn get a better polishing result and possibly a lower cost to finish the floor.

Visual facets of processed concrete
There are three visual facets of processed concrete - the degree to which the surface is cut, the level of clarity of reflection of the cut surface and decorative enhancements.