Floor Flatness and Levelness

Understanding F-number requirements for commercial and industrial floors

One of the things that distinguishes a high tolerance floor is its F-number requirement. F-numbers were developed in the 1980s to provide a systematic, quantitative way to indicate the flatness and levelness of a concrete floor. The higher the F-number, the flatter or more level the floor. There are actually three F-numbers that are used for concrete floors, depending on whether the floor will have a random traffic pattern or defined traffic aisles.

Dan Dorfmueller Dan Dorfmueller
Flatness is determined by finishing while levelness is determined by strike-off. Dan Dorfmueller
  • FF—This number is used to indicate the flatness of a random-traffic floor. FF is measured as the curvature of the floor over a 2-foot interval. Take a grid of 2-foot intervals over the entire floor and put the values through an equation and you get the FF value as an indication of the waviness of the floor. The FF value is primarily a result of how good the finisher was at working the surface to achieve a flat floor. The FF value of a driveway, for example, might be 10 while the FF of a superflat floor could be as high as 125.
  • FL—The second number indicates the levelness of a random-traffic floor and is measured over a 10-foot interval. Again, take all of the 10-foot readings, add them up, and put them through an algorithm (an equation) and you will get the FL value. FLis primarily a result of how good the contractor was at setting the side forms and striking off the concrete and has almost nothing to do with the skills of the finisher.
  • F-min—It's important to understand that the F-min value is only applicable to defined-traffic floors, that is, floors with defined aisles along which traffic is to travel. These are typically warehouses that use high-mast lift trucks. There is no direct correlation between FF/FL and F-min. F-min is measured using a profileograph, an instrument that measures the deviation both longitudinally and transversly from perfectly flat.

Allflat Consulting
F-min is measured using a traveling profileograph, which simulates
the wheel pattern of a high-mast lift truck. Allflat Consulting

On a random-traffic floor, FF/FL should be specified both for the entire floor (overall minimum) and for the area within a single bay (local minimum). "The most consistent mistake specifiers make is the failure to specify both overall and minimum-local F-numbers," says Allen Face, Allen Face & Company. "The overall numbers are for the entire floor; the minimum local values apply to each individual square defined by the sawcuts." The minimum-local value is generally specified as 67% of the overall value, which allows a single bay to be slightly less flat and level than the overall floor.

GTS, Inc.
Flatness and levelness are measured on random
traffic floors using a Dipstick. GTS, Inc.

FF and FL are measured using either the Dipstick from Face Construction Technologies or the F-meter from Allen Face & Company. The Dipstick was the original device used to measure these values and is stepped across the floor. The F-meter rolls along a defined line.

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