When Ryan Klacking, president of Syncon, Inc., Dearborn, Mich., came on board as the polishing concrete subcontractor at a 23,000-square-foot airplane hangar project in North Carolina, he knew he needed to deliver a quality job. The owner, an aviation company that owns about 35 hangars throughout the United States, was looking for an alternative to its usual epoxy flooring system for its next hangar. In its research for a new floor finish, the aviation company decided to give polished concrete a try. For Klacking, the challenge was on.
Why polished concrete?
The aviation company had installed “hanger white” epoxy floors in its previous projects. These flooring systems looked good at first, Klacking says, but within six months the floors were scratched and showing signs of wear. The owner was also paying for removal and replacement of the floors every five years to maintain a clean and aesthetic appearance for its properties.
The aviation company found several characteristics of polished concrete that made it an ideal flooring choice for its hangar, including durability and abrasion resistance. Both the application of a hardener/densifier and the way the polishing process itself affects concrete on a microscopic level gives the polished surface a high abrasion resistance factor.
The owner also wanted an attractive floor. A properly polished concrete floor will display a high level of clarity and reflection due to refinement, offering light reflectivity and a surface that looks clean and professional. And a well-maintained polished concrete floor will continue to offer aesthetic appeal far beyond the five-year life span the owner was seeing with its epoxy floors.
Another important factor on the mind of any owner is cost. “On a cost-per-square-foot basis, installation of polished concrete is comparable to epoxy,” Klacking says. “But maintenance and longevity wise, polished concrete wins out.”
Working with a GC
The general contractor brought Syncon on as the polishing subcontractor early enough in the project that Klacking was able to work with the construction team in planning the pour. He met with the general contractor and concrete subcontractor to provide an overview on the polishing process and explain how certain characteristics of a mix and the finishing processes can make or break a polishing job.
“We mentioned making sure the concrete did not exceed 4,000 psi so we would not have problems removing the cream coat and exposing the salt and pepper finish the owner wanted,” Klacking explains. “Also, we added that we would like to achieve a minimum floor flatness rating (FF) of 50 and a floor levelness rating (FL) of 35.
Klacking says the owner did not require a gloss measurement reading, but his team set a goal to achieve a gloss reading in the 60s. Additionally, he advised a 12-foot by 12-foot saw cut layout to minimize the possibility of out-of-joint cracking.
Klacking says the concrete subcontractor brought up questions about the finishing process. “We told them we wanted the floor power troweled, just not burned, and not to use hand trowels in the area to receive the polished floor because these areas always stand out on a polished floor because in hand troweled areas the finish is typically softer and always seems to have more exposed aggregate and surface pitting."
The polishing process
Klacking’s team used a wet grinding method to start the job, using a Prep/Master 3030 grinding unit from Substrate Technologies, Inc. “Wet polishing assures a consistent cut on the floor in that it keeps the diamonds cool and lubricated which allows them to work more efficiently,” Klacking says. “When diamonds get too hot they can cut differently in different areas of the floor.”
Syncon started grinding with an 80-grit metal bond abrasive then moved to a 100-grit hybrid metal/resin bond abrasive to grind past the floor’s cream cap to open up the floor and expose the aggregate for the salt and pepper look.