For big box retail stores, it's not only the levelness and flatness of a floor that counts, it's also the ability of a floor to reflect light that matters. The trend for large retail stores is to leave the concrete exposed, making it the surface finish. Increasingly, floors also are being integrally colored, burnished, and polished.

Rick Smith, vice president of operations and a senior consultant with Structural Services Inc. (SSI), Richardson, Texas, says that owners are more concerned now about the reflectance of floors because lighting and maintenance costs become lower and glossy-looking floors have customer appeal. The challenge for contractors is to achieve, protect, and maintain the specified level of reflectiveness during the construction process and the challenge for owners is to maintain the delivered reflectiveness over time.

Measuring reflectance

Measuring reflectance is done with glossmeters—electronic devices that emit infrared signals that are then treated mathematically to provide numbers that correspond to how well light is reflected from a surface. They are used to provide information about a wide variety of materials and manufactured products. Glossmeters usually include memory in them so that several readings can be plotted and statically averaged. To take a reading, the instrument is held against a flat concrete surface and a reading is captured at a specified angle (typically 30 degrees) to the horizontal surface. The gloss measurements are captured within a sealed collection point under the gloss meter and are independent of the ambient light source and intensity if the measurement unit is tight to the concrete surface. The number it reports falls within a range between 0 and 100. Smith says their retail clients' desire readings of 40 and higher. A freshly waxed vinyl composite tile (VCT) floor might exhibit gloss around 75, which is precisely the look retailers are attempting to generate with concrete floors. As a general rule, flatter dense surfaces are more reflective and achieve higher numbers.

Measuring reflectiveness during the construction process is relatively new and information is beginning to accumulate that will help to determine what improves and maintains, and what reduces reflectiveness. SSI takes measurements after troweling operations are complete, after wet curing blankets are removed, when the curing residue is removed, after liquid chemical treatments are applied, and when scrubbing and polishing steps are completed just prior to owner possession. The collection procedures are easy. Three random readings per column bay are collected and averaged to achieve a score. Each bay must achieve the specified overall gloss value (SOGV) for the project or the surface may be scrubbed and high-speed burnished until it complies with the specification. No single reading may fall below the minimum local gloss value (MLGV)—the lowest quality of gloss that the client expects.

What affects gloss numbers

Here are some of Smith's observations about what improves and reduces scores:

  • The mixture design must provide the finisher with uniform, predictable setting characteristics and sufficient paste to facilitate a dense burnished surface.
  • Reasonable ambient conditions during placement, including temperature, humidity, wind velocity, air quality, and lighting, are specified to support the finisher's efforts.
  • The floor must be burnished by the finisher and exhibit obvious gloss at the conclusion of final troweling. Gloss values in the 10 to 30 range appear to setup the project for higher ultimate gloss values. Lower gloss values may require more intensive scrubbing, high-speed burnishing, or potentially dry or wet diamond polishing to meet the clients' expectations. The skill and dedication of the finisher is very important to the result.
  • Proper cleaning of the floor slab concurrent with wet curing blanket removal sets the stage for optimum densifier application, penetration, and chemical reaction.
  • Using soft bristle brushes (compared to hard bristles common to the maintenance industry), soft janitorial pads, or diamond impregnated janitorial pads for final scrubbing and high-speed burnishing increases gloss readings.
  • Chemically or physically aggressive environments or inappropriate maintenance equipment, chemicals, or procedures have a negative impact on long-term gloss scores.

Similar to the way that the F-Number System changed the industry for the better, gloss values may soon be used by contractors as a tool to differentiate themselves from their competition and by owners as a nonsubjective measure for compliance. The idea that floors can be cast and finished with fewer people in less time is counter-productive when architectural slabs with high-gloss expectations are specified. A hard-troweled floor with proper attention given to the details will get the best numbers and repeat customers.