Technical-Resources-for-Concrete-Contractors
Technical-Resources-for-Concrete-Contractors
Technical-Resources-for-Concrete-Contractors
Technical-Resources-for-Concrete-Contractors
Technical-Resources-for-Concrete-Contractors
Technical-Resources-for-Concrete-Contractors

Division 3 versus Division 9 Floor Flatness Tolerances

ASCC Position Statement #6

Division 3 specifications for concrete floor flatness typically include FF requirements. The specifications also require that floor tolerance measurements be taken in accordance with ASTM E 1155-96, ”Standard Test Method for Determining FF Floor Flatness and FL Floor Levelness Numbers.” Thus, the F-number measurements for meeting Division 3 requirements incorporate the following:

  • Point elevations measured at regular 12 in. (300 mm) intervals along each line;
  • Measurement lines distributed uniformly across the test section;
  • Minimum number of readings required for statistical approach; 
  • Measurement lines not within 2 ft (0.6 m) of any slab boundary, construction joint, isolation joint, block-out, penetration, or other similar discontinuity; and;
  • Flatness measured within 72 hrs. of concrete placement.

Division 9 specifications for concrete floors to receive a floor covering typically provide floor flatness requirements in terms of an allowable gap under an unleveled straightedge. There is no ASTM procedure for this measurement. Straightedge measurements for Division 9 incorporate the following:

  • Continuous measurement at any gap under the straightedge; 
  • Indefinite number of straightedge locations on the floor;
  • No minimum or maximum number of readings;
  • Measurements typically made with the straightedge crossing construction joints or column blockouts, and near penetrations; and
  • Measurements made just prior to floor covering installation, which can be from 4 to 18 months after concrete placement.

Division 3 and 9 floor flatness tolerances are obviously not compatible. There is only a rough correlation between FF numbers and the gap under a straightedge. F-number measurements don’t include flatness variations indicated by straightedges placed across construction joints and column block-outs. And floor flatness changes with time (due to curling) make it impossible to predict the flatness when floor coverings are installed, based on FF measurements made soon after concrete placement.

Want to learn more? Download the full Position Statement! 

Browse all Position Statements