A growing trend in versatile, beautiful flooring solutions that can also last a lifetime is the use of polished concrete. To attain such visual aesthetics, contractors first look at the concrete itself.
Working with Concrete
There’s a time-honored adage about concrete, whether processed or not, that it is consistently inconsistent. Every single pour will be different from the next, with variations in color, cracking and overall flatness. However, the general goal is for the floor’s flatness to be as even as possible while pouring a new slab, as well as preparing the surface of an existing slab for finishing.
This being said, when pouring a new concrete floor, it’s a good idea to look at a polished finish as part of a total flooring system that includes 1) a concrete mix design, 2) curing, 3) a finishing method and 4) the actual polishing process. A concrete slab that’s poured with the polishing process in mind will greatly enhance the end result.
Working with existing concrete slabs, results are determined by the quality of the existing concrete. Color variations, contaminates, cracks, patterns left by previous floor covering, stains, nail holes, patched areas and flatness all affect the newly polished appearance.
The polishing process usually includes grinding down the surface to reveal different levels of aggregate within the concrete or the addition of decorative aggregates, such as recycled glass, landscaping stone, nails, nuts, bolts, sea shells and others, seeded into the surface for decorative purposes. There are three common aggregate choices to consider when it comes to polished concrete floors:
1. Cream Polished or Surface Cream: the top layer of the concrete is made from troweled cement paste that contains the cement fines of the mix. Only 1/32 – 1/64-inch is removed from the slab surface, resulting in little or no aggregate exposure. This is a popular, economical style; the cream is the purest, most consistent in color, has the fewest imperfections and can be stained any color.
2. Salt and Pepper: the layer just below the cream made from fine aggregate – sand and very small stone that gives the concrete a “salt and pepper” look. To achieve this look, 1/64 – 1/8-inch of the cream is removed by grinding the surface, exposing small amounts of medium aggregate randomly throughout. The ideal time to start the grinding process is within 7 days of pouring the concrete slab, which helps to expose just the right amount of aggregate.
3. Exposed Aggregate: the layer below the cream and salt and pepper made from coarse aggregate within the concrete mix. To reach this layer, 1/8 – 1/4 -inch is ground from the surface, removing the top two layers. This process should start almost immediately after a concrete slab has been poured to within 3 days of pouring to achieve the aggregate exposure desired. Course aggregate comes in three sizes: small, medium and large.
After achieving the type of aggregate exposure, the concrete is polished to a desired clarity of reflection. 1) ground to a flat shine, 2) honed to refined even appearance, 3) semi-polished, for crisp, smooth look or 4) highly polished, for a mirror effect.