Polished concrete

Black basalt polished concrete floor

Polished concrete is concrete that has been treated with a chemical densifier and ground with progressively finer grinding tools. The grinding tools are usually progressive grits of diamond grinding cup wheels and diamond polishing pads. Typically, concrete is not considered polished before 400 grit, and it is normally finished to either the 800, 1500, or 3000 grit level. Stains and dyes are often applied to enhance polished concrete as well as other options such as scoring, creating radial lines, grids, bands, borders, and other designs.

Benefits

Polished concrete is considered a good sustainable design flooring option because it makes use of the materials already present. Most modern buildings are built on a concrete slab; polishing the exposed concrete eliminates the energy and material consumed by applying a floor covering. It is something to consider when building or modernizing towards a more green solution.

Polished concrete floors are low-maintenance, as they are more durable and easier to clean than many flooring options. Its relatively high coefficient of friction can make it non-slippery. Polished concrete reduces dust mite and allergen problems, and does not support mould growth. Anecdotal evidence suggests highly reflective polished concrete reduces lighting needs and improves natural lighting, but as of yet there has not been a study to confirm this. Polished concrete flooring is hard wearing and will not chip or dent like softer surfaces such as timber and mopping with warm soapy water once a week is the only maintenance required.

LEED 2009 standards contain guidelines for using polished concrete flooring to qualify for LEED credits.

New or retrofit

In simple terms, the process of polishing concrete is similar to sanding wood. Heavy-duty polishing machines, for example concrete grinder, are used to gradually grind down surfaces to the desired degree of shine and smoothness. The closest equivalent example would be polished granite or marble.

Polished concrete floor installation is categorised into two types: new floors, and retrofit floors.

New floors

New polished concrete slab

New floors require less work resulting in lower costs, but there are a few things to be aware of before a new concrete floor can be polished. Firstly the slab can contain a decorative aggregate. The two most common aggregates are river stone, granite, and black basalt mix, however the aggregate can be almost anything. The finished surface of the concrete will need to be finished to a high standard to facilitate the polishing process. During the finishing phase any decorative aggregates such as seashells or car parts can be dropped into the surface of the concrete. Builder needs to be aware as early as possible if the concrete is to be polished so that the final finish is of the best quality.

Retrofit floors

Retrofit floors can be done in two ways. The existing floor slab can be cut or sanded and the natural aggregate will be the feature or a topping slab with a minimum thickness of 50 mm can be added on top of the existing slab.

Process

New polished concrete floor

Process involved in polishing concrete:

1. The concrete floor is cut 3–4 times depending on the finished surface. This can be done wet or dry depend on the site situation.
2. The surface is then grouted with cement to correct imperfections and fill air bubbles.
3. Two more cuts are done after grouting.
4. A clear liquid hardener referred to as an indensifier is then worked over the surface for about 1 hour. The indensifier will provide a glossy look to the finished floor. It will also give the floor extra strength.
5. The floor is then left overnight for curing before 3 more polishing grit are done.
6. Lastly the concrete surface will be sealed with a stain and block out sealer to reduce water and oil staining.
7. Timing of delivery depends on the type of equipment that a contractor uses. It can be expected that a 32" grinder will average 600 square feet per hour per grit, and a large Bobcat mounted 3-headed grinder can grind 2,000 square feet per hour per grit. The Bobcat grinders have limited availability on the east and west coast.

Notable buildings with polished concrete

1. Solyndra, Fremont, CA – President Obama and Governor Arnold Schwarzenegger walked on this Diacon polished concrete floor in May of 2010
2. California Academy of Sciences, San Francisco, CA
3. Saddleback Church Teen Center, Lake Forest, CA
4. Planes of Fame Air Museum, Chino, CA
5. California State University, Sacramento, CA by Pacific Decorative Concrete
6. University of New Mexico Arena "The Pit" Albuquerque, New Mexico

See also

• LEED
• USGBC
• Burnishing
• Grinding
• Concrete grinder