Polishable concrete overlays are becoming very popular due to their ease of maintenance and beautiful high-gloss finish, especially in high-profile retail and commercial spaces. In space where existing concrete slabs cannot be polished or if the floor has major flaws, such as spalled areas, carpet tack holes and extensive patchwork, they will still show through after polishing. And in terms of decorative options, existing polished floors are limited to the application of topical color. As an economical alternative to polishing imperfect concrete floors, more and more contractors are now installing polishable concrete overlays, not only to hide existing flaws, but also to give them more decorative versatility.

Polishing a concrete overlay requires more coordination of efforts and attention to detail than polishing a conventional concrete slab. Here are some tips from concrete polishing specialist Tom Zilian of Madstone Concrete, Barrington, R.I., on how to polish cement-based overlays successfully.

Placing the overlay

• For polishing, you need a very flat floor, free from ripples and smoothing marks, says Zilian, who uses a self-leveling polishable concrete overlay system, Param 6000.
• Be ready for any contingency that may occur while the pour is in progress by keeping an organized mix station and plenty of backup tools and staff on hand. “Timing is everything,” says Zilian. “We use lots of manpower and two or three mixing stations to make sure a fresh batch is continuously being delivered to the pour line. We also have a high degree of expertise behind the gauge rake and smoother.”
• If you want to seed the surface with glass or other aggregates, wait no longer than 10 minutes after the overlay has been smoothed.

The polishing process

• Always use a planetary grinder when polishing concrete overlays, and begin polishing no later than 24 hours after overlay placement.
• Use metal-bond diamond tooling for the initial grinding and honing stages (80 grit, then 100 grit). “We make sure we grind deep enough to cut past the air voids around the aggregates if we have seeded them into the overlay at the time of pouring. It is very important to keep the machines steady and watch your pull backs. We keep our rpms a little higher when grinding overlays,” says Zilian.
• Apply a densifier. Zilian prefers to use a colloidal silica-based densifier for his polished overlay projects (such as Duraamen’s Hermetix), because its extremely fine particle size seems to yield better results than traditional sodium- or potassium-based densifiers. When applying a densifier to concrete overlays, Zilian recommends using twice the spread rate as conventional concrete because of their porosity.

Final burnishing

• For the final polishing stages, Zillian uses a series of diamond-impregnated pads (200 grit, 800 grit, and 3,000 grit). “We turn up the rpms as high as the machine will run. We also take the weights off at this point, turning our planetary grinder into a burnisher,” he says.
• Before burnishing, apply a floor conditioner to help protect the floor and enhance the shine. “We have one installer use a pump sprayer to apply the floor finish and another to smooth it out. Within minutes we can be high-speed burnishing.”

Maintaining polished concrete: As a maintenance regimen for polished overlays, Zilian recommends daily vacuuming to remove abrasive particles, along with periodic mopping with a neutral or slightly PH detergent to keep up the shine. He also recommends high-speed burnishing with a 3,000-grit diamond-impregnated pad once a year to revitalize the shine.

You can watch detailed polishing process here. Please feel free to contact us to discuss your project.