For many decades concrete floors have been specified with tolerances similar to 1/8″ in 10′. Without any accurate or systematic method of collecting data these tolerances were specified, but not achieved unless utilizing specialized strip pour Super Flat techniques (which is excessive and not required).
The F number system was developed in the mid 1970’s and is based on the idea of creating a systematic, repeatable and informative method for measuring and specifying tolerances for concrete floors. Regardless of your location around the world, the “F Number” system provides specifiers with the ability to decide on the correct tolerance, provide contractors with a meaningful tolerance to construct and owners with a facility that works.
There are two variations of the F Number system: “FF/FL” tolerances (floor flatness/floor levelness) for random traffic floor surfaces and “Fmin” tolerances for defined traffic (AGV) floor surfaces. Each system has a defined purpose for a given environment; random traffic or fixed traffic.
The basis of the mathematics for the FF/FL system is that data is collected uniformly across the entire placement area (pour by pour) and statistically averaged to arrive at final overall F number. F numbers are improved by reducing the frequency and amplitude of bumps and valleys on the surface of the floor. This is attained by using special placing and finishing techniques for any given tolerance. Fmin tolerances are based on correlating the allowable tolerances for the specialized AGV equipment (longitudinal and transverse) across its wheel base and axle separation to define the necessary strip placement techniques for any given tolerance.
|Floor Usage:||Typical Tolerance:||Methods:|
|Office Areas: Thick Finishes||FF20/FL18||
|Office Areas: Thin Finishes||FF25/FL18||
|Warehouse Areas: Foot Traffic||FF25/FL18||
|Warehouse Areas: Random Forklift Traffic||FF40/FL30||
|Warehouse Areas: Defined Wheelpath Traffic||Fmin40 to Fmin100*||
|Elevated Slabs||FF20/FLna ** #||
* Fmin tolerances vary with the actual lift truck manufacturers performance data.
** FL tolerances are not applicable to suspended slabs due to camber and deflection.
# Improved flatness tolerances are not possible in elevated slabs without the use of double pan float machines which may pose a safety concern.
The following is a list of areas we recommend for consideration when designing a new floor:
- CSA A23.1 includes reference tables for specifying FF/FL tolerances. ACI302 and ACI 117 discuss the recommended practices for floor construction and tolerance achievement.
- FF80 is twice as flat as FF40 and FF40 is twice as flat as FF20.
- Tolerance improvement is achieved through revised construction placing and finishing techniques and NOT from increases in the number of cement masons on a pour.
- FL (levelness) tolerances do not apply to cambered or suspended floor slabs.
- Floor tolerances MUST be measured within 72 hours following construction if they are to be used for conformance purposes.
- Constructed floor tolerances generally decline as the concrete dries in jointed floors because of curling of slab edges caused by the normal drying shrinkage of the concrete. Tolerance losses of up to 50% may occur.
- Fmin tolerances do not apply to random traffic areas and FF/FL tolerances do not apply to defined traffic areas.
- Existing facilities can be measured to define suitable tolerances for new projects (plus an allowance for curling) — through this website you can request pricing for getting facility measurements.
- Many testing companies own the necessary equipment to measure floors specified with FF/FL tolerances.
- Owners, specifiers and contractors all win with the use of this measurement system.
- See also Dipstick Calibration.
If you have any questions, please feel free to e-mail.