We’ve all see that twinkle of freshly fallen snow; that reflective sparkle ice crystals give off when light hits the flakes in a certain way. Now try to envision that same effect on a polished concrete floor. That was the challenge an architect presented to Roy Bowman, president of Concrete Visions, Inc., Tulsa, Okla., for 5,200 square feet of floor on two levels at a corporate training center in Plano, Texas. Bowman and his team delivered on that challenge with a polished concrete overlay seeded with mirrored glass.
Making an idea reality
When Bowman first heard of the architect’s idea to have polished concrete that twinkles like snow, he took a hard look at the existing building’s concrete floors and knew he couldn’t achieve the desired look with what he had to work with. He turned to a polishable concrete overlay, with his crew testing various products to ensure the process could actually be done. They ultimately chose CTS Cement’s Rapid Set TRU Self-Leveling overlay for the project.
From there, the Concrete Visions crew prepared several 12-foot by 12-foot mock-ups using different amounts and various sizes of mirrored glass seeded on top of the overlay. The mirrored glass was painted on all sides, and the mirror finish was exposed only after it was ground. The architect chose the mock-up that best made her idea a reality and gave Concrete Visions the job.
The overlay process
Bowman says the most challenging part of any overlay project is planning and preparation. Because a self-leveling overlay is a highly flowable liquid working to seek out any and all nooks and crannies, a contractor has to seal all penetrations on the floor and install transition strips at doorway thresholds. This prevents an overlay from running through cracks, between the floor and walls, and even out the door. Concrete Visions used a floor patch and foam spray to seal penetrations; Bowman recommends zinc transition strips for thresholds and starting and stopping points.
Before an overlay placement starts, Bowman says a contractor needs a placing plan with well thought out points on the floor for where the pour can stop and/or start. An overlay placement should start in one area with a crew working its way to an exit point, being careful not to double back on any of the overlay that has been placed. A contractor also needs to plan starting and stopping points if the overlay application stretches beyond one day and have an idea for stopping points in the case of an unexpected event or if the application process stalls. After taking in all these considerations, the Concrete Visions crew decided to hire a subcontractor to pump the overlay.
“Without the pump, we wouldn’t have been able to place this overlay in one day. That means we would have had stopping and starting points and transitions which can lead to more problems,” Bowman explains.
It took Concrete Visions four hours to place the overlay using the pump, which saved the crew a day on labor and the cost of having four additional men on the job. The pump also allowed for a placing plan that included a scissor lift for the second-floor overlay process, allowing the pump hose to enter and exit through an upstairs window.
With the overlay plan set, Concrete Visions set out to create a bonding plane, or a textured surface to which the overlay could bind. This could have been done with a shot blaster or grinder and the application of a primer, but Concrete Visions chose an epoxy and sand method. “We knew we had good absorption on the floor to soak up that epoxy. Because of the space constraints on this job and some tight areas, this was the best way to go. It was probably an overkill step, but it eliminated the need for a primer and would help us avoid any moisture issues,” Bowman explains.
Concrete Visions ground a 2-mil profile on the floor to bring up any previous coatings and to leave a texture. Crew members then applied 10 mils of epoxy and covered it with 2,000 pounds of sand; they removed excess sand the next day. This process left an extremely textured “bite” and allowed the epoxy to bind to both the floor and the sand.