Why we Measure a Concrete Surface

The difference between a well polished and a poorly polished concrete floor determines whether a Durable & Impervious finish is acheived.
A Roughness Average (RA) Meter is used to measure the surface.

A well-polished concrete surface is much more capable of withstanding everyday wear and tear. This is why the American Industry developed the use of an RA meter, to read the texture of the surface before sealing. So you know to what level of polish was achieved.

Concrete is naturally porous, so with the application of grouts and densifiers into the concrete slab, the micro cracks and pinholes are filled, and the surface becomes impervious. The RA Meter will read any imperfections in the surface from the cracks and pinholes just as it will with scratches.

The ST115 standard is not a pass/fail, right/wrong standard. It offers a range of surface textures to consider. While achieving an impervious surface should not be compromised when the NZ Building Code requires it, the finished texture from polishing is flexible to suit the application you have. Factors that may influence that decision are indoor/outdoor areas, wet areas, level of gloss required, life expectancy and budget. Once a level of polish has been agreed to then measuring that surface before sealing confirms what you asked for is what you are getting.