Mike Schroer, an owner of Bob's Produce Ranch, wanted a minimum maintenance floor to enhance their fresh food-oriented neighborhood grocery. A grocery store design team representative suggested polished concrete. Schroer investigated, installed the floor, and now hopes to use polished concrete in other stores. “We only need a buffer to shine the floor. We don't have to strip and apply wax,” he says. “When the floor is wet, it becomes a little sticky under foot. That added customer safety for us and made our insurance company happy.”
The project began with a meeting between the grocery store owners and Polished Concrete Images, Sauk Rapids, Minn., to discuss the 5200-square-foot installation. The agenda included the floor's character, color options, decorative sawcuts, slipperiness, maintenance, and joint detail. The design called for polishing the floor with color and stencil additions. The owners wanted a consistent salt and pepper exposure of aggregate. “The floor curled at the control and construction joints,” says Josh Theis, project manager. “We explained that larger aggregate sizes would appear in those areas when they were polished.”
Theis began with a 40-grit diamond embedded metal bond pad to level and expose the salt and pepper sized aggregate. A pass with the 150-grit diamond followed at a 90-degree angle to the first. Theis then switched to a combination of 100- and 200-grit resin-bonded pads on a planetary grinder with three heads. “Some people will not mix grit size,” he says. “I find mixing grit size at the beginning does not leave adverse effects and it flattens the slab more quickly. I do not mix grit sizes at final stages.”
Next, he used 400-grit pads grinding at 90 degrees from the previous pass to avoid repeated forward and back movements. Then the slab was prepared for color. Sometimes a floor is cleaned with an auto scrubber, but Theis says this floor was clean enough to remove the dust with a vacuum system. Theis applied acetone-based dye by Ameripolish, Springdale, Ark., at 400 to 600 square feet per gallon using an acetone resistant sprayer. He took safety precautions and had good ventilation, which an Acetone application requires. Acetone is very dangerous in poorly ventilated areas when there is any ignition source nearby.
Theis applied vinyl logo stencils cut by Modello Design, National City, Calif., to the floor surface before the acetone-dye application. The gray concrete became the negative area where color did not penetrate. For the red apple and leaf, the positive stencil design was cut but the vinyl wasn't removed. The area around the stencil received raw sienna color, and then the stencil was peeled away to color the red and green areas with a small sprayer.
To protect the slab, Theis applied the lithium densifier Pentra-Sil and then Pentra Guard to protect against stains—both by Convergent Concrete Technologies, Orem, Utah. The application of Pentra Guard after 800-grit pads can leave surface application marks but these marks were removed with a 1500-grit resin diamond bond pass. After the 1500-grit resin bond diamond, the floor was cleaned and turned over to the owner. The owners had workers install a custom-color two-part polyurea joint filler made by Versaflex, Kansas City, Mo., to blend the control joints with.