Polishing concrete might be thought of as an art as much as a science. To be blunt, techniques exist that could be used to make a floor “appear” to be within contracted specs, even when it’s not. Most importantly, one cannot possibly verify that a job has been done correctly without consistent means to precisely measure results. And that’s where gloss truly “shines.”
Gloss has been defined as “the attribute of surfaces that causes them to have shiny or lustrous, metallic appearance.” Basically, it’s an aspect of how something looks, and it can rival the importance of color when it comes to consumer impact. When it comes to polished concrete, a number of factors can affect the final surface gloss: the smoothness achieved during polishing, the amount and type of coating applied, and the quality of the substrate. Because of these multiple variables, it is imperative that there be a way to define “quality,” or a job well done. And that requires a measurement.
Gloss is measured in gloss units (GU), by a glossmeter, which shines a known amount of light at a surface and quantifies the reflectance. The angle of that light can be different. ISO 2813 and ASTM D523 (the most commonly used standards) describe three measurement angles to measure gloss across all surfaces.
- (60°) Universal Measurement Angle: All gloss levels can be measured using this standard glossmeter measurement angle.
- (85°) Low Gloss: For improved resolution of low gloss, this angle is recommended for surfaces which measure less than 10GU when measured at 60°. This angle also has a larger measurement spot that will average out differences in rougher surfaces.
- (20°) High Gloss: This angle gives improved resolution for high gloss surfaces (70GU and above when measured at 60°). It is also more sensitive to haze effects on the surface.
So, what does all this mean to you as a polishing contractor, construction manager or building owner? Because grinding and polishing concrete is a multi-faceted, complex process with numerous opportunities for error, many factors (lighting, angle, time, etc.) can affect the basic “look” of a polished concrete floor. Flaws may not be readily apparent, with even a detailed examination. Our industry professionals should understand that the only way to know for sure about the gloss of a surface, is by taking an accurate measurement. And this requires a gloss meter, either as an individual unit or part of a comprehensive system, such as the Runyon Data Services. Whatever you decide, Grace Hopper, the first to devise the theory of machine-independent programming languages, may have summarized the reasoning best: “One accurate measurement is worth a thousand expert opinions.”