Questions about Polishing Concrete Floors
Polishing a floor can give it a glossy, rich finish that shines in a Wal-Mart or a luxury auto dealership. Even better, polishing is chemical-free, which makes it a godsend in this age of crackdowns on volatile organic compound emissions.

But a decorative concrete contractor will have some tough questions to ask about this trendy technique. How well does it work with other decorative techniques? What about maintenance? What is the real reason big discount store chains and other commercial clients are specifying polished finishes on their floors? Let's take that last question first.

The number one reason stores are turning to polished concrete is cost, says Kyle Wiggins, sales and marketing manager at Innovatech Products & Equipment. "The average store spends $1.70 per square foot per year maintaining their vinyl composite tile floors," he says. "VCT floors have a lifetime of five to six years and have to be replaced as well. Polished concrete costs about $0.10 per square foot per year to maintain, and polished concrete will never need to be replaced. If a store properly maintains their concrete floors then they should never need to be repolished."

Not only does polished concrete last longer with cheaper maintenance than other finishes, but it increases the ambient light in a store to boot. "A polished floor provides a finished floor with light reflectivity that is still durable and easy to maintain," says John R. Abrahamson, president and managing director of HTC Professional Floor Systems.

Getting slippery
Of course, cost savings don't mean much if shoppers keep slipping and falling on floors. It's a fair question: Is a high shine slippery? Does a higher diamond grind finish compromise slip resistance?

"I guess you would have to define 'slippery,'" Wiggins says."A polished concrete floor at 3,000 grit has better slip resistance then a waxed VCT floor."

A higher shine does not make the floor less slip-resistant, Abrahamson says, because in the absence of any wax coating or sealant, the concrete is still in a natural state, and friction still takes place on the surface. "The shine factor is misleading. We have learned that shine means slippery because we have been walking on wax and other such topical coatings when we've seen shine. If we lived in Europe, and walked on diamond-polished natural stone rather than waxed surfaces, we would not be so conditioned. Shiny isn't necessarily slippery. Waxes and coatings are."

A higher shine does not mean more maintenance either. Actually, a highly polished floor is easier to maintain, says Poinsettia Byrd, who does senior technical sales and support with VIC International Corp. "The higher polished floors hold their shine better," she says. "And in independent testing, a high diamond grind finish can be more slip-resistant than a power-troweled floor."

Wiggins agrees. "The maintenance of polished concrete is the same at every level. It is not a maintenance-free floor but a low-maintenance floor. The floors need to be cleaned on a regular basis. There are several products that can be added to the cleaning water to keep the floor shine at a maximum."

However, Abrahamson sees it differently. "It's very easy to maintain a high shine, but a higher shine does require more dedication than a low shine."

RetroPlate marketing director Peter Wagner, for his part, says yes and no. "In actuality, a floor that is polished to a higher level is closed up tighter, lessening the ability of soil or spills to adhere to the floor. Perceptually, the higher the shine, the more visible soil or spills will appear to the eye, raising the need to clean more often. An 800-grit or 1,500-grit's higher reflectivity will 'visually' require more frequent cleaning."

A finish to 800 grit will meet or exceed OSHA and ADA recommendations for static coefficient of friction, Wagner says. "Although some floors at 1,500 grit may also pass, RetroPlate has third-party testing showing that an 800-grit finish passes both dry and wet, for leather, neolite and rubber."

Polishing standards vary even within chains, observes Wagner. "Some stores receive a full-blown 'metals to resins' grinding and polishing, while many others only receive resins. The difference, in addition to the cost, is that the lower-end metal-grit diamonds are generally required to remove all the laitance, inclusions, and so on. These steps are what produce your final clarity in your floor, while the resin polishing steps are literally only addressing the surface. A floor which receives both metals and resins will deliver a floor with both clarity and shine, while the floor just with resins only provides shine."

Considering color
Another question of particular interest to decorative concrete contractors is how polishing interacts with other decorative techniques.

Wiggins says polishing can change the color of integrally colored and color-hardened concrete. "Depending on what types of diamonds are used and the process — wet or dry — the color could come out a shade or two lighter or darker."

However, the challenges of polishing integrally colored and color-hardened concrete are no different than the challenges of polishing standard grey concrete, Abrahamson says. "As long as the concrete is solid and structurally sound, any concrete can be polished," he says. "Polishing enhances and enriches the color, and allows you to choose the level of shine."

The effect depends on the diamond tooling used to polish, Byrd says. "Some tools leave a darkening effect on the floor. With good diamond tools, the color of the floor is enhanced."

However, Byrd warns, the color-hardened top layer of concrete can be removed through too much grinding. "You must be concerned with the cosmetics of the integrally colored concrete."

Grinding off part of the color when polishing a stained or dyed slab is also very easy to do, Wiggins says. "This could leave an uneven or blotchy look in the slab when finished. It is very important to know at what step in the process to dye or stain, harden and seal the concrete slab."

Also, consider flatness and levelness when polishing colored concrete, says Wagner. "With dry shakes, an uneven floor, and potentially uneven broadcast and placement of the dry shake, you can end up with areas where you grind through the dry shake entirely, exposing the base slab."

It's important to apply a densifier or hardener prior to polishing colored concrete surfaces, Wiggins says. "When diamond grinding is done before the polishing process, it will grind away the power-troweled surface, leaving a surface with a lot of pores in it. This surface makes it very easy for a concrete dye or stain to penetrate farther down into the slab. The problem with doing this is the surface is left very weak and prone to wear with traffic. The solution to this problem is to harden or densify the surface to prevent this wear."

Densifying the concrete makes the wear surface much more abrasion resistant, keeps the concrete from dusting, and helps it retain shine, says Abrahamson.

Byrd is also bullish on densifying. "As an integrally colored floor is consistent throughout the slab, the wear pattern can alter the color of the floor. Shake-on color hardener can actually get worn off. Densifying will increase abrasion resistance, protecting both surfaces from excessive wear patterns."

Wagner says that while the addition of a densifier before polishing helps both integrally colored and dry shake floors, the integral floor will benefit more. "Integrally colored floors tend to be softer than regular concrete, whereas dry-shake floors are going to be two to three times harder. The densifier provides abrasion resistance, oil and water repellency and dust-proofing for the integral, while the main benefits for dry shake, in addition to the polished look, are the increased oil and water resistance, along with the dust-proofing. Dry shake is a high percentage cement product, so the dusting is important."

The timing of when the densifier goes into the floor varies between integral and dry shake, and even between dry shake applications, Wagner says. "In looking at integral, you will want to perform your grinding up through 100-to-200 grit, and then apply the densifier. The reason for this timing is that a harder, densified floor will polish in a better, tighter scratch pattern. As with natural stone, the harder the surface, the tighter the scratch pattern, and the tighter the scratch pattern, the more abrasion resistance and higher gloss to your finish.

"With dry shakes, the less grinding the better. The method with which the floor was finished, whether pan-troweled or plastic blade, will change how you have to perform your grinding step, and what grinding steps you have to perform will dictate when to apply your densifier."