Although the James M. Bennett High School in Salisbury, Md., will not be submitted for certification through LEED, the Wicomico County Board of Education knew that all future schools built in the district would have to earn LEED certification. With maintenance budgets shrinking and LEED in the back of the owner's mind, the architect set out to find a flooring solution that fit into LEED requirements, would be aesthetically pleasing and would require less maintenance than traditional VCT (vinyl composition tile). The solution was to use the existing concrete sub floor and mechanically process and highly refine the surface to a polish with diamond abrasives for a polished concrete floor.
My company, Cuviello Concrete, was selected as the subcontractor to process the concrete to a polished finish. The job consisted of 41,000 square feet of corridors of uncolored concrete, a 7,000-square-foot black integrally colored cafeteria, 7,000 liner feet of edges, 463 corners and 3,159 linear feet of saw cut joints.
The polishing project was originally bid to receive a multi-colored dye application. Due to a concern as to how well the specified dyes would hold up to long-term ultra violet light, vapor transmission, pH variations in the concrete and the possibility of improper maintenance, the architect and school board decided to remove the dye application. For aesthetic appeal, they instead opted to use colored glass in school colors - red and white - and other decorative aggregate seeded into the surface at the time of placement. The surface would be ground to expose the seeded aggregates, honed and polished to a 1,500-grit finish.
A pre-planning project meeting was held with all parties whose work would affect the outcome of the finished floor. The meeting included the owner, architect, general contractor, concrete flooring subcontractor, the ready mix producer and me, the polishing subcontractor. In the meeting I explained how the aggregates would need to be seeded along with mix design and finish work requirements. I also emphasized the goal of the floor was not to achieve a finish that would resemble terrazzo but to achieve a consistently inconsistent exposure of aggregate; any expectation of a terrazzo consistency would set me up for failure and everyone else for disappointment.
Together with the concrete flooring subcontractor, my team produced a mock-up showing various densities of glass and aggregates that ranged from one half pound up to a pound and a half per square foot. Over the next several months the concrete flooring contractor poured the floors and seeded the aggregate by staging it in 5-gallon buckets every 10 feet along the pour, ensuring each area would receive the same amount of aggregate.
A floor protection plan protected the floor in the 18 months that spanned the time between the floor pour and the polishing. A janitorial-grade acrylic floor finish was applied to help protect the slab from stains. In addition, all trades were told they were working over a finished floor and that anyone caught cutting pipes, running equipment that was not diapered, or did damage to the surface from negligence would result in a back charge.
On the job
In the initial grinding phase we used a Prep/Master 4430 to grind the concrete anywhere from 1/8 inch to ¼ inch. To finish the grinding phase and throughout the honing and polishing phases we used two Lavina 32 Pro units. With the initial grinding steps being the most demanding we chose to use the Prep/Master 4430 because of its gear drive, weight for heavy grinding, 44-inch grinding path and ability to refine the floor through the use of 24 abrasives being driven in an intertwining rotary motion. The Lavina was chosen because it is lighter, easier to finesse into smaller areas and quickly refines the floor through the use of 18 abrasives being driven by six individual satellite heads in a planetary motion.