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Floor Flatness

Floor Flatness (FF) numbers provide a convenient means for specifying floor profiles for flatness and in statistical terms. Since many of the concrete placement specifications are being specified using ASTM E1155 and ACI 117 it is important that tile contractors understand how these methods of measurement evaluate the flatness of a floor profile and the effect it will have on the cost of preparing the surface for tile. This type of specification method can cost additional time and money to prepare floors with acceptable tolerances to receive ceramic tile and provide the owner with functional and aesthetically pleasing installations. Awareness and understanding of these terms and attention to their requirements can substantially impact costs of preparing floors to receive ceramic tile and stone and must be taken into consideration during the bidding process.

An understanding of concrete industry standards is crucial to the tile contractor, as ACI 117 and the ASTM E1155 F-Number System allow, in most cases, much greater levelness and flatness tolerances than current tile industry standards. If a tile contractor is not familiar with these differences when bidding a project, they may unknowingly accept significant concrete substrate preparation work in order to meet the specified tile tolerances, or simply to meet the high level of quality and finished appearance that most professional tile contractors and owners expect. Similarly, design professionals must do a better job in recognizing these potential conflicts, and implement better coordination in project specifications. Accepting and making provisions in the project specifications for the reality of substrate preparation is a more reasonable solution than the traditional (and unreasonable) specification boilerplate excuse that the tile contractor be responsible for “whatever it takes” to prepare and execute the work to industry standards, and that “commencing work constitutes acceptance of the substrate” and all its deficiencies. It is a common mistake for the tile contractor to assume entitlement to a change order increase or backcharge for additional substrate preparation during construction. As a result, the tile contractor may be saddled with a lose-lose situation in having to choose between absorbing substantial additional preparation costs, or rejection of the finished appearance of ceramic tile. It is the duty of the tile contractor to recognize potential substrate problems before submitting a bid. NOTE : The tile contractor should request all FF reports issued on the project. FF numbers are generally taken within 72 hours of slab placement and may change over time due to conditions, such as curling, settlement, loading and the removal of shoring. The tile contractor is strongly encouraged to have the floors re-evaluated by a third party just prior to installation.

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NTCA Reference Manual | 2024 / 2025

Chapter 2 | Substrates