Haze, in accordance with ASTM D4039, is defined as the numeric difference between the specular reflectance at 60° and 20°. Fortunately, fancy definitions aside, it is also a concept that we’re basically familiar with. Think of a rainy night and the blooms around the headlights of an approaching vehicle. In this case, it’s the rain affecting the light, which is an example of “transmission” haze. But when it comes to polished concrete, or any otherwise highly-reflective surface, what concerns us is “reflection” haze, where instead of falling water reducing the visible quality, microscopic surface textures diffuse the reflected light. This results in a “milky” finish and/or halos around surface reflections.
And what causes haze? Unfortunately, the list is long and notorious, to include: resin transfer from diamonds, an improper polish, dried densifier, and guard like products or impregnator not removed from the surface. And let’s not forget cleanliness issues, temperature extremes, ageing and oxidation. On a more positive note, haze can also be measured, so it can, and must be accounted for when ensuring polish work is up to specs.
Haze is expressed in Haze Units (HU) and is measured by a glossmeter. But not all glossmeters have the capability to measure haze, for they must have additional detectors 2º either side of the specular angle. Assuming that you have the proper meter and have taken a reading, the key number to remember when it comes to haze, is 10. For the Polished Concrete Appearance Chart, which is an industry standard, is only applicable with a haze reading below 10 HU. This cutoff was established because as long as haze is below 10 HU, then a Distinctness of Image (DOI) reading is much more difficult to manipulate compared to a standard gloss reading, making for an excellent indicator of overall grinding/polishing quality and surface sustainability.
So, what’s the takeaway on haze? When considering the Surface Prep industry, it’s one of the more important factors that can definitely make or break your day. And whether you are a grinding/polishing contractor or the recipient of the finished surface product, it is in your best interest to account for haze and have the capability to accurately measure this fundamental, yet critical surface aspect. A comprehensive system, such as the Runyon Data Services, will give you this ability.