Verification of substrate flatness is a mandatory quality control step. Using a long, high-quality straightedge, the installer checks for low or high spots across the entire installation area. Industry standards usually define the allowable tolerance based on the type of tile and the grout joint width. If the floor fails the flatness check, the installer must apply a self-leveling underlayment or perform localized grinding and patching to ensure the floor is within the specific flatness requirements for the material being used.
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How should installers verify substrate flatness during installation?
Installers verify flatness by using a 10-foot straightedge placed in multiple directions across the floor. Any deviations or dips that exceed the manufacturer's or industry guidelines (like those from the TCNA) must be addressed with self-leveling compounds.