Floor Flatness and Levelness

Chapter 4

Chapter Topics

• Measuring floor flatness and levelness• The 10 ft (3m) straightedge method• F-number system• Factors affecting floor flatness and levelness

Definitions

• Flatness– Waviness or bumpiness of slab surface– Smooth

• Levelness– Tilt or slope of slab surface

Measuring Flatness and Levelness• Gap under a 10 ft straightedge– Oldest method– Measures only floor flatness; not levelness– Generally less satisfactory way of measuring

• F-number system– Measures floor flatness and levelness– Must be used if floor exceeds 10,000 sf (ACI 301)– Measurements in accordance with ASTM standard

The 10 ft Straightedge Method

• Measured within 72 hours• Place an unleveled 10 ft straightedge on slab• Rests on two high spots• Measure gap at any point under straightedge

between two high spots• 100% compliance with straightedge not realistic• Four out of five measurements more realistic

F-Number System• Measure within 72 hours

• FF – floor flatness FL – floor levelness

• To get F-numbers– Measure surface elevations at 12 inches on-center– FF (bumpiness) calculated over 24 inch length– FL (tilt) calculated over 10 ft length

• F-number pair always written in order: FF/FL

• Higher F-numbers: the flatter and more level

F-number System• Two different sets of F-numbers– Specified Overall Value (SOV)– Minimum Local Value (MLV)

• Check specifications for requirements

• ACI 302 provides recommendations

• Measure in accordance with ASTM E 1155

• FL should not be measured on sloped slabs

Factors Affecting Flatness

• Concrete workability, finishability, and setting time;

• The window of finishability• Sun, wind, rain, temperature extremes, • Amount of sunlight on the slab;• Timeliness of concrete delivery;• Uniformity of concrete slump, as delivered;• Consistency of final setting time; and• Site accessibility.

Factors Affecting Levelness

• Accuracy of edge forms

• Quality of initial strikeoff

• Wet screeds are harder to get higher FL

• Smaller strip placements are easier to get higher FL

End of Chapter 4