Ensure concrete finishing specifications include all the information required for floor slab tolerances. Specifying single values for flatness and levelness may result in ambiguous requirements. F-Number and straightedge methods require two sets of values to ensure the expected results are clearly stated.

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Providing:
Specifications, Quality Assurance, FLOOR SLAB FLATNESS & LEVELNESS
Inspections & Investigations
for your Construction Projects By David Stutzman, AIA, CSI, CCS, SCIP, LEED AP
ABSTRACT: Background When defined traffic patterns exist
Traditionally allowable tolerances such as for narrow aisle and
Ensure concrete finishing
specifications include all the of concrete floor slabs were automated warehouses special
information required for floor slab determined by checking the slab consideration must be given to
tolerances. Specifying single surface with a 10 foot concrete placement and tolerance
values for flatness and levelness measurements. These conditions
straightedge. Common tolerances
may result in ambiguous are not addressed by ACI 117.
were 1/8 inch or 1/4 inch in 10
requirements. F-Number and
feet.
straightedge methods require two F-Number Method
sets of values to ensure the The fallacy of the straightedge
expected results are clearly stated. The ASTM standard, in place for
method was the location of the
two decades, establishes the
measurement. Depending on
FILING: where the measurement was
method for measuring F-Numbers.
UniFormat™ The method uses a statistical
made, the slab may pass or fail the
analysis of measured points 12
A1030 - Slab on Grade specified tolerance. Until recently,
inches apart taken along straight
B1010 - Floor Construction no standard procedure existed for
lines in a prescribed pattern within
taking straightedge
each sample panel. Each sample
MasterFormat™ measurements.
panel must exceed 320 sf, must
03 30 00 - Cast-In-Place Concrete In 1979 Allen Face introduced the be at least 8 ft. wide, and must not
Face Floor Profile Numbering cross a construction joint.
KEYWORDS: System (F-Numbers) to remove the
The ACI standard sets
Flatness, Levelness, F-Numbers, ambiguity of measuring floor
Straightedge, Specified overall recommended F-Number
flatness and levelness. F-Numbers
values, Minimum local values, tolerances for various concrete
use dimensionless symbols to
Allen Face floor slab construction qualities.
designate flatness and levelness.
To specify F-Numbers correctly,
F-Numbers formalized in 1987 by
REFERENCES: ASTM E1155 and ASTM E1155M
two values are required for
flatness and levelness:
ACI 117 - Standard Specifications were adopted by the American
for Tolerances for Concrete Concrete Institute as the standard  Specified Overall (SOFF and SOFL)
Construction and Materials for specifying floor tolerances in
ASTM E1155 - Standard Test  Minimum Local (MLFF and MLFL)
1990 in ACI 117.
Method for Determining FF Floor
Flatness and FL Floor Levelness  FF Floor Flatness - variation from Floor Surface
SOFF SOFL
Numbers surface plane (bumpiness) Classification
ASTM E1155M - Standard Test Conventional 20 15
Method for Determining FF Floor  FL Floor Levelness - variation from
Moderately Flat 25 20
Flatness and FL Floor Levelness horizontal plane (pitch)
Numbers (Metric) Flat 35 25
Specifications referencing ACI 117
Very Flat 45 35
for tolerances may rely on
F-Numbers or manual straightedge Super Flat 60 40
methods to determine floor slab
tolerances for random traffic F-Numbers must be measured
pattern floors which are typical for within 72 hours of placing the
most uses. However straightedge slab. This ensures that the
measurements are not permitted F-Numbers are measuring the
for very flat and super flat floors. concrete contractor's quality. If the

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measurements are delayed, 90% of the samples must not Flat floors are suitable for thin set
shrinkage, curling, and other exceed column 2 and 100% of the ceramic tile, vinyl tile and similar
factors outside the concrete samples must not exceed column finishes and for conventional fork
contractor's control can influence 3 of the table below. truck traffic in warehouses. Flat
the results. floor classification is the most
Maximum Gap
Floor Surface stringent tolerance that should be
Levelness tolerances apply only to
Classification 90% 100% expected for suspended slabs.
slabs-on-grade and suspended Compliance Compliance
slabs that are shored when tested. Very flat floors are usually
Levelness tolerances do not apply Conventional 1/2 inch 3/4 inch restricted to high-end industrial
to sloped or cambered floors. Moderately applications where high speed
3/8 inch 5/8 inch
Flat fork trucks and other high-
ACI 117 sets the Minimum Local
Flat 1/4 inch 3/8 inch production equipment are used.
values at 60% of the Specified
Overall values, unless specified Very Flat N/A N/A Super flat floors are appropriate
otherwise. The Minimum Local for very limited applications with
Super Flat N/A N/A
values are the minimum tolerances random traffic such as television
for the floor to be usable. Defects The familiar 1/8 inch in 10 feet production studios to minimize
exceeding the Minimum Local tolerance is not an option with ACI camera vibration.
values normally require grinding, 117. This may present difficulties
filling, or replacement to correct for specifying slab tolerances for
Specification Tip
the defect. applied floor finishes, such as Select the method: F-Number or
For a slab to be acceptable, the wood strip flooring. Some floor manual straightedge. Reference
cumulative Overall Values for the finish manufacturers require more ACI 117 for tolerance compliance.
entire slab must meet or exceed stringent tolerances than can be
Allen Face provides an F-Number
the Specified Overall values, and tested using the straightedge
sample specification. Include the
all locations must meet or exceed method. Consult the finish
minimum Specified Overall and the
the Minimum Local values. flooring manufacturer's
Minimum Local values for both
instructions for acceptable
flatness and levelness.
Straightedge Method substrate surfaces.
For the manual straightedge
In the June 2010 edition of ACI Floor Classifications method, specify the maximum gap
117, the straightedge method
The floor classifications above are for 90% and 100% compliance.
description was greatly expanded.
Now the standard establishes a for random traffic patterns. More
procedure for measuring flatness stringent tolerances require
with a straightedge. Note that additional straightening
levelness cannot be determined operations, time, and cost to Add Your Comments
with a straightedge. ACI 117 sets ensure compliance. Very flat and We invite your comments. Visit our
minimum sampling requirements super flat floors require blog and add your comments.
to help ensure a statistically specialized equipment and www.conspectusinc.com/blog
representative set of specially trained mechanics to
measurements. One sample must achieve the results.
The information contained in this
be taken for every 100 sf of floor Conventional floors are not document is offered for educational
area. Samples must be taken suitable for applied finishes. These purposes, only, and not as technical
parallel, perpendicular, or at a 45 floors are used for utility spaces advice suitable for any particular
degree angle to the longest and are usually left exposed. project or specific condition. Technical
construction joint of the test area.
Moderately flat floors are consulting is unique to the facts of a
The following chart shows the suitable for carpeted finishes in particular condition, and Conspectus
maximum gap between the floor commercial buildings and low recommends that a specialist be
surface and the bottom of the 10 speed vehicular traffic in industrial consulted to determine solutions for
foot straightedge. Note that buildings. each specific condition.