Floor flatness and levelness

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
• 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
• 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

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