07 Aug Polished Concrete
Although concrete polishing is not a new process, it is being applied with new and dramatic effect in the design world. Building on the time-proven processes of terrazzo and hard surface (granite, marble, and natural stone) finishing, architectural polished concrete is becoming a finish of choice for commercial, service, and residential environments.
There are many factors that affect the quality of a concrete substrate including mix design, geography, additives, and finishing methods. It is important to understand that all concrete will not look, polish, or wear the same. When properly poured, placed, and finished, concrete yields a smooth stable surface. Hydration occurs when cement, water, aggregates, and chemical additives combine to form calcium hydroxide and ultimately concrete.
In time and with the proper moisture retention during the curing process, concrete reaches its maximum natural performance characteristics. However, there are ways of improving and enhancing those characteristics. Polishing can add physical and aesthetic value as well as increase the concrete’s lifespan and performance.
Since the concrete substrate will become the finished floor, it is important to take precautions against surface staining, damage, and contamination. Construction processes, on a substrate that is specified for a polished concrete finish, must be treated differently than most construction environments. Overspray from painting, patching compounds like drywall mud and mortar, hydraulic oils from cutting operations and lifts, and surface spills can all pose a threat to the success of the final product. Care must be taken to safeguard against surface damage or staining.
Inadequate or improper protection of the floor surface during construction will likely result in inconsistencies in the polished concrete finish. Protection is critical when considering polished concrete as a finished floor system, it is necessary to understand the advantages and limitations of the system. Generally speaking, any environment which could utilize sealed concrete as a wearing surface can benefit from the addition of surface polishing. Environments that deal with caustic or acidic materials which can attack or etch concrete will not.
There are two processes required to produce a polished concrete finish that will last. Chemical densification employs the use of penetrating agents to alter the substrate, closing the pores by causing a permanent internal modification to the concrete’s make-up. Mechanical densification is the actual process of grinding, honing, and polishing the concrete to densify the surface by closing the pores of the substrate physically.
Either densification process alone will not produce a surface that can exhibit and maintain the maximum aesthetic and performance values. Combined, they yield a stable polished concrete finish.
Chemical Densification is the process of applying a reactive silicate (lithium, potassium, or sodium) to the concrete to chemically harden and dust-proof the surface. Reactive hardeners cause an internal chemical reaction at and below the surface that permanently alters the concrete’s composition by converting calcium hydroxide and free lime into more stable, insoluble tri-calcium silicate compounds. Unlike a topical sealer which forms a protective film over the surface, densifiers become an integral component of the concrete substrate.
Typically, densifiers are applied and scrubbed into the substrate for thirty minutes. The surface must remain wet and the densifier cannot be allowed to dry on the surface. Surface drying will generally produce a crystalline, white film which is very difficult, and sometimes impossible, to remove. The preferred method to clean the surface during the hardener application process is with a walk-behind or ride-on auto scrubber. It is very difficult to properly clean the floor without the use of appropriate equipment and a good, high pH or general purpose cleaning solution.
Mechanical Densification is achieved via grinding, honing and polishing processes that incorporate the proper equipment with an appropriate combination of down pressure, rotation speed, and diamond or carbide media. The process begins with the lowest grit needed and progresses sequentially higher to the specified finish level. The starting and ending points will be determined by a combination of: the condition of the substrate to be polished, the desired look and gloss level, the end use of the space, and the concrete’s inherent properties.
The ultimate goal is the balance of production and lifespan from the media used. If a diamond is not wearing, it is not working. If a diamond is wearing too rapidly, it is in too soft of a bond for the surface. Neither end of the spectrum is effective or cost efficient. When a diamond is in the proper bond for the surface it is working on, both the production rate and wear rate will be consistent. This allows for accurate time and material estimates. As a general rule the softer the surface – the harder bonded diamond required, and the harder the surface – the softer bonded diamond required.
Benefits and Limitations
All installed floor systems have specific requirements for successful installation. It is important to verify that the product manufacturers written guidelines govern the installation process. Adherence to instructions is critical for maintaining the manufacturer’s warranty; neglecting these instructions will almost certainly void the warranty. Proper product selection based on end use, appropriate scheduling with other trades, testing/compliance to product moisture requirements, and installation per industry Best Practice methods are necessary for a quality flooring installation.
Ease of maintenance is one of the greatest benefits of a polished concrete surface since there is no sealer to chip or peel and waxing and refinishing is not necessary. From utility service areas to dramatic interior spaces, polished concrete is utilized in many different environments. However, polished concrete is not generally recommended for areas that are subject to harsh chemicals, acids, or other caustic elements that can etch or contaminate the concrete surface. Consult the system manufacturer for project suitability.
Regular maintenance is vital to the long term welfare of all floors. There is not a surface available that can be used without cleaning and maintenance to remain in optimum condition. Typically, the floor is subjected to the most abuse in any normal business. Keeping the floor in good condition takes a little forethought and a consistent effort. The first step to maintaining floors is preventing as much soil, debris, and potential damaging agents from being introduced to the environment in the first place. Interior and exterior walk-off mats can minimize the amount of sand, water, and foreign matter that are tracked onto the floor. Limiting contaminants will simplify the maintenance process.
There are unique maintenance procedures available for polished concrete. Many manufacturers have developed processes incorporating diamond impregnated cleaning/buffing pads for use in conjunction with floor scrubbing equipment. These methods allow for continuous re-polishing of the surface during routine cleaning operations which can help maintain an optimum surface gloss and finish.