Received an email with an interesting technical question:What level of flatness do we need in a concrete slab for a ceramic tile installation - using the F-number system?Note:Measuring concrete levelness and flatness using the F-number system for ceramic tile & stone installations may be over and above what is needed. Typically measuring FF/FL tolerances would be for projects such as warehouses where forklifts or machinery requires tight concrete levelness and flatness tolerances.And our Laticrete Technical Support reply:Please note that the American Concrete Institute's (ACI) Floor Flatness (FF) / Floor Levelness (FL) are typically used by concrete specifiers / masons to pour their floors to specific tolerances. Typically, the following are the FF #'s which roughly correlate to the respective floor tolerances:FF 25 is roughly equivalent to a single ± 1/4" defect in 10' FF 50 is roughly equivalent to a single ± 1/8" defect in 10' FF 100 is roughly equivalent to a single ± 1/16" defect in 10'Tile Council of North...