Concrete Polishing
What is Concrete Polishing?
Concrete Polishing is the art of using a specialized grinding machine to grind an existing or new concrete floor to create a polished smooth finished surface. The options for the look and color of the finish are virtually unlimited.
Concrete polishing is rapidly becoming one of the most popular floor finishes. Common floor finish options are carpet, vinyl tile, linoleum vinyl tile, hard tile, and concrete polishing. What differentiates concrete polishing from other finishes? Concrete polishing uses the actual concrete floor slab as the finished surface.
How do you create a polished concrete surface?
A specialized concrete polishing machine uses abrasive pads of varying grit to cut (grind) a scratch pattern into the concrete surface. This process is a multistep operation. It starts using heavier grit pads and then transitions to finer grit pads. There are two factors that define the look of your finished concrete polished floor: aggregate exposure and shine.
What is aggregate exposure?
Aggregate exposure is the amount of large and small stones, rocks, and sand you will see when you look at the finished polished floor. Finishes that expose the larger stones in the concrete are called coarse aggregate finishes. Those that expose only the small rocks and sand in the concrete are called fine aggregate finishes. The finishes that expose just the cement and sand paste are called cement fine finishes.
The Concrete Polishing Council, a council of the American Society of Concrete Contractors, defines the exposure finish in three levels: A, B, and C with A being the fine finish and C being the coarsest aggregate finish. This chart defines the three levels by the percentage of the cement fines, fine aggregate, and coarse aggregate exposure in the finished floor.
What is the gloss appearance?
The gloss or shine of the slab is the appearance which can vary incrementally from flat to satin to polished to highly polished. The flat being the dullest least reflective finish and the highly polished being the shiniest glossy finish.
The Concrete Polishing Council defines the gloss appearance finish in levels 1-4, 1 being the flat finish and 4 being the glossy, highly polished finish. This chart defines these levels by measuring the distinctness of an image reflecting in the floor finish. This is measured on a scale of 1-100 using an image clarity meter or gloss meter. The number 0 being the flattest and 100 being the most highly polished finish.
The image clarity meter also registers how much haze there is in the slab. The haze is the cloudiness or milky appearance of reflecting images in the floor finish. The haze factor should be below a minimum level to be acceptable for a polished floor.
How do you accomplish the desired floor polished finish?
If your desire is to have more of the large aggregate exposed, you would grind more with the heavier grit pads until you have the reached the desired amount of aggregate exposure. Then you transition to lighter pads and continue to use pads of lesser grit until you reach the desired level of gloss finish. It is important that the polishing contractor incrementally uses each level of grit and does not skip levels while polishing in order to get a long-lasting finish.
What other options can be used during polishing to create variety and ensure a quality finish?
- The grinding can either be done dry or wet depending on the work environment and the desired finish.
- Densifiers are added during particular steps in the grinding process which makes the surface harder and more impenetrable.
- Color can be added by using an additive to the concrete when it is mixed. This is integral colored concrete mix. Other options for adding color can be added by applying them directly to the surface of the concrete. This is a spray applied acid stain, concrete dye, or a colored densifier.
- Different aggregates can be used and exposed to achieve any number of unique finishes.
- The particular placing and finishing technique used while placing the concrete slab can be used to achieve a consistent or random looking polished finish.
