Floor Flatness and Levelness
Chapter 4
Chapter Topics
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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
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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