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TECH TIPS
www.conspectusinc.com
Vol12.10.01 ©2012 Conspectus Inc.
Page 1 of 2
Providing compete Floor Slab Flatness & Levelness
construction specifications By David Stutzman, AIA, CSI, CCS, SCIP, LEED AP
documentation, systems
and performance Background such as for narrow aisle and
descriptions, and risk and automated warehouses, special
quality advisory services. Traditionally allowable tolerances of consideration must be given to
concrete floor slabs were determined concrete placement and tolerance
Conspectus's Tech Tips received the by checking the slab surface with a measurements. These conditions are
national Communications Award from 10 foot straightedge. Common not addressed by ACI 117.
the Construction Specifications tolerances were 1/8 inch or 1/4 inch
Institute September 2011. F-Number Method
in 10 feet.
ABSTRACT: The fallacy of the straightedge
Ensure concrete finishing method was the location of the The ASTM standard, in place for two
specifications include all the measurement. Depending on where decades, establishes the method for
information required for floor slab the measurement was made, the slab measuring F-Numbers. The method
tolerances. Specifying single values may pass or fail the specified uses a statistical analysis of
for flatness and levelness may result tolerance. Until recently, no standard measured points 12 inches apart
in ambiguous requirements. F-
Number and straightedge methods procedure existed for taking taken along straight lines in a
require two sets of values to ensure straightedge measurements. prescribed pattern within each sample
the expected results are clearly In 1979 Allen Face introduced the panel. Each sample panel must
stated. Face Floor Profile Numbering System exceed 320 sf, must be at least 8 ft.
FILING: (F-Numbers) to remove the ambiguity wide, and must not cross a
UniFormat™ of measuring floor flatness and construction joint.
A4010 Standard Slabs-on-Grade levelness. F-Numbers use The ACI standard sets recommended
A4020 Structural Slabs-on-Grade dimensionless symbols to designate F-Number tolerances for various
B1010 Floor Construction flatness and levelness. F-Numbers concrete floor slab construction
MasterFormat™ formalized in 1987 by ASTM E1155 qualities. To specify F-Numbers
03 30 00 Cast-In-Place Concrete and ASTM E1155M were adopted by correctly, two values are required for
the American Concrete Institute as flatness and levelness:
KEYWORDS: the standard for specifying floor Specified Overall (SOF and SOF )
Flatness, Levelness, F-Numbers, tolerances in 1990 in ACI 117. F L
Straightedge, Specified overall Minimum Local (MLF and MLF )
F Floor Flatness - variation from F L
values, Minimum local values, Allen F
Face surface plane (bumpiness) Floor Surface SOF SOF
Classification F L
F Floor Levelness - variation from
REFERENCES: L Conventional 20 15
ACI 117 - Standard Specifications for horizontal plane (pitch)
Tolerances for Concrete Construction Moderately Flat 25 20
and Materials Specifications referencing ACI 117 Flat 35 25
ASTM E1155 - Standard Test Method for tolerances may rely on
for Determining FF Floor Flatness and F-Numbers or manual straightedge Very Flat 45 35
FL Floor Levelness Numbers methods to determine floor slab
ASTM E1155M - Standard Test Super Flat 60 40
Method for Determining FF Floor tolerances for random traffic pattern
Flatness and FL Floor Levelness floors which are typical for most uses. F-Numbers must be measured within
Numbers (Metric) However straightedge measurements 72 hours of placing the slab. This
are not permitted for very flat and ensures that the F-Numbers are
super flat floors. measuring the concrete contractor's
When defined traffic patterns exist quality.
TECH TIPS
www.conspectusinc.com
Vol12.10.01 ©2012 Conspectus Inc.
Page 2 of 2
If the measurements are delayed, Maximum Gap Very flat floors are usually restricted
shrinkage, curling, and other factors Floor Surface to high-end industrial applications
outside the concrete contractor's Classification 90% 100% where high speed fork trucks and
Compliance Compliance other high-production equipment are
control can influence the results. Conventional 1/2 inch 3/4 inch
Levelness tolerances apply only to used.
slabs-on-grade and suspended slabs Moderately 3/8 inch 5/8 inch Super flat floors are appropriate for
that are shored when tested. Flat very limited applications with random
Levelness tolerances do not apply to Flat 1/4 inch 3/8 inch traffic such as television production
sloped or cambered floors. studios to minimize camera vibration.
ACI 117 sets the Minimum Local Very Flat N/A N/A
values at 60% of the Specified Overall Super Flat N/A N/A Specification Tip
values, unless specified otherwise. The familiar 1/8 inch in 10 feet
The Minimum Local values are the tolerance is not an option with ACI Select the method: F-Number or
minimum tolerances for the floor to be 117. This may present difficulties for manual straightedge. Reference ACI
usable. Defects exceeding the specifying slab tolerances for applied 117 for tolerance compliance.
Minimum Local values normally floor finishes, such as wood strip Allen Face provides an F-Number
require grinding, filling, or replacement flooring. Some floor finish sample specification. Include the
to correct the defect. manufacturers require more stringent minimum Specified Overall and the
For a slab to be acceptable, the tolerances than can be tested using Minimum Local values for both
cumulative Overall Values for the the straightedge method. Consult the flatness and levelness.
entire slab must meet or exceed the finish flooring manufacturer's For the manual straightedge method,
Specified Overall values, and all instructions for acceptable substrate specify the maximum gap for 90% and
locations must meet or exceed the surfaces. 100% compliance.
Minimum Local values.
Straightedge Method Floor Classifications
The floor classifications above are for
In the June 2010 edition of ACI 117, random traffic patterns. More stringent
the straightedge method description tolerances require additional
was greatly expanded. Now the straightening operations, time, and
standard establishes a procedure for cost to ensure compliance. Very flat
measuring flatness with a and super flat floors require
straightedge. Note that levelness specialized equipment and specially
cannot be determined with a trained mechanics to achieve the Add Your Comments
straightedge. ACI 117 sets minimum results. We invite your comments. Visit our blog
sampling requirements to help ensure Conventional floors are not suitable and add your comments.
a statistically representative set of for applied finishes. These floors are
measurements. One sample must be used for utility spaces and are usually Like it? Share it!
taken for every 100 sf of floor area. left exposed. Tweet or Email your friends
Samples must be taken parallel, Moderately flat floors are suitable for
perpendicular, or at a 45 degree angle carpeted finishes in commercial
to the longest construction joint of the buildings and low speed vehicular The information contained in this document
test area. traffic in industrial buildings. is offered for educational purposes, only,
The following chart shows the Flat floors are suitable for thin set and not as technical advice suitable for any
maximum gap between the floor ceramic tile, vinyl tile and similar particular project or specific condition.
surface and the bottom of the 10 foot finishes and for conventional fork Technical consulting is unique to the facts
straightedge. Note that truck traffic in warehouses. Flat floor of a particular condition, and Conspectus
90% of the samples must not exceed classification is the most stringent recommends that a specialist be consulted
column 2 and 100% of the samples tolerance that should be expected for to determine solutions for each specific
must not exceed column 3 of the table suspended slabs. condition.
below.
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