The American Concrete Institute has adopted F-Numbers as its standard for the specification and measurement of concrete slab flatness and levelness.
Ff, or "flatness F-Number," defines the maximum floor curvature allowed over 24" (600 mm) computed on the basis of successive 12" (300 mm) elevation differentials. Fl, or "levelness F- Number," defines the relative conformity of the floor surface to a horizontal plane as measured over a 10' (3.03m) distance. The higher the F-Numbers, the more level or flat the slab.
For reference, the Maple Flooring Manufacturers Association (MFMA) requires that the general contractor provide a concrete slab, troweled smooth and flat to a tolerance of 1/8" in a 10' radius for all gymnasium floors.
The MFMA does not acknowledge the use of F-Numbers to measure levelness/flatness tolerances in gymnasium slab applications. If a F-Number is specified for flatness, it must be at least the equivalent of MFMA's standard 1/8" in 10' radius tolerance, and the following conditions must be adhered to in order to meet MFMA's standard slab specification:
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The F-Number measurement must be taken two (2) weeks prior to the maple floor installation.
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The measurement process must include all construction joints over the entire concrete slab.
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The MFMA flooring installer must be present during the entire measurement process.
If the above conditions are not met during all Ff/Fl Number measurements, MFMA does not recommend the acceptance of any Ff/Fl test results. MFMA's standard 1/8" in 10' radius flatness specification should be enforced.
If you have additional questions, contact your MFMA flooring contractor or MFMA's Technical Director at 888/480-9138.
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