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F Numbers

The F-Number system produces a quantifiable representation of a concrete floor’s flatness (bumpiness) and levelness (tilt) for random-traffic usage. This tolerance method is systematic, repeatable, non-subject & meaningful making it ideal for owners, specifiers, floor users and concrete floor contractors alike. The F Number system is very practical for concrete floor contractors who have learned what results they can achieve using different methods of construction.

F Numbers are measured and calculated using the procedures defined by ASTM E1155 “Standard Test Method for Determining FF Floor Flatness and FL Floor Levelness Numbers”. ASTM E1155 defines two facets of concrete floor surfaces: 1) an “FF” floor flatness value and 2) “FL” floor levelness value. The FF “floor flatness” value provides information about the floor smoothness or bumpiness and FL “floor levelness” values provide information about relative alignment to a horizontal plane.

FF numbers vary based upon the amplitude and spacing of bumps or valleys in a floor surface. These bumps and valleys can be reduced in size and spacing using different methods of construction to produce floors with improved levels of flatness and levelness for specific uses (See CSA A23.1 Table 21 classifications). Floor Flatness is a critical consideration for all exposed concrete surfaces and surfaces with thinly applied finishes. F-Numbers are linear, such that FF 40 is twice as flat as FF 20. There are no FF or FL equivalents to a gap under a 3 m straightedge. FF flatness values can be specified for all types of random traffic concrete surfaces, but FL levelness does not apply to sloping surfaces or suspended slabs (due to camber & deflection).

Note that “Super-flat” concrete floor surfaces subject to automatic guided vehicle traffic (not random traffic) must use a special “Fmin” tolerance system that is not defined by either ASTM E1155 or CSA A23.1.

CSA A23.1 mandatory F-Number compliances for random traffic floors:

1. Only the F-Number system shall be used in accordance with the procedures set forth in ASTM E1155.
2. Floors shall be classified as per Table 21 of CSA A23.1 (see below).
3. Surfaces shall be measured within 72 hours of each concrete placement.
4. FL levelness tolerances shall not apply to suspended slabs or inclined surfaces.
5. The average of all the placements must exceed the Specified Overall FF/FL Values.
6. Individual placement results may vary around the Specified Overall Value but must not fall below the Minimum Local Value (60% of overall value).
7. Corrections shall be made by grinding unless otherwise specified.

CSA floor classifications:    Flatness/levelness:    Examples:

A”    Conventional  FF 20 FL 15  Foot traffic and thick finishes
B”    Flat  FF 25 FL 20  Exposed concrete and thin applied finishes
C”    Very flat  FF 35 FL 25  Ice rinks and low-rack forklift environments.
D”    Extremely flat  FF 45 FL 30   High-rack forklift environments.

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Geoffrey K Kinney
gkinney@flattech.ca
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