ASCC Position Statement #35

ACI 117-06 and ACI 117-10 “Specification for Tolerances for Concrete Construction and Materials” require F-numbers to be measured within 72 hours after slab concrete placement. This was not always the case. ACI 117-90 included no time requirement for the measurement of floor flatness, FF, and the commentary stated the reason:

“Since neither deflection nor curling will significantly change a floor’s FF value, there is no time limit on the measurement of this characteristic.”

The statement in the commentary indicating that curling will not significantly change a floor’s FF value has since been shown to be incorrect by measurements published in “The Concrete Floor Tolerance/Floor Covering Conundrum,” Concrete International, July 2003 . This is why ACI 117-06 and ACI 117-10 now require that FF measurements be made within 72 hours. 

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