Designation: C 485 – 09

Standard Test Method for

Measuring Warpage of Ceramic Tile1
This standard is issued under the fixed designation C 485; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A
superscript epsilon (´) indicates an editorial change since the last revision or reapproval.

1. Scope 2. Referenced Documents

1.1 This test method covers procedures for measuring di- 2.1 ASTM Standards:2
agonal and edge warpages of the following categories of C 242 Terminology of Ceramic Whitewares and Related
ceramic tile: Products
1.1.1 Square Tile, 2 by 2 in. (51 by 51 mm) or larger, that are 2.2 ASTM Adjuncts:
nominally flat, of uniform overall thickness, and have a smooth Warpage Gage for Ceramic Tile3
face of one of the types: unglazed, bright glazed, matte glazed,
or finely crystalline glazed. 3. Terminology
1.1.2 Oblong Tile, no facial dimension smaller than 2 in. (51 3.1 Definitions:
mm), that are flat, of uniform overall thickness, and have a 3.1.1 tile—see Definitions C 242.
smooth face of one of the types: unglazed, bright glazed, matte 3.1.2 warpage—curvature of a flat tile measured as devia-
glazed, or finely crystalline glazed. tion of the tile surface from a true plane along the edges or the
1.1.3 Square and Oblong Tile, no facial dimension smaller diagonals. The deviation is measured at the mid-length of an
than 2 in. (51 mm), that are flat, but have an irregular face such edge or diagonal, expressed as a percentage of the length of the
as embossed, sloped, bumpy, wavy, coarsely crystalline, or edge or diagonal, and called convex or concave with respect to
wire-cut textured. the face of the tile.
1.1.4 Nonrectilinear Tile, larger than 4 in.2 (26 cm2), that
are flat and of uniform body thickness with smooth or irregular 4. Summary of Test Method
face, such as hexagonal, diamond, Spanish type, and so forth. 4.1 This test method consists of measuring the deviation
1.1.5 Trim Tile meeting one of the descriptions in 1.1.1- from a straight line at the midpoint between reference points on
1.1.4 except that only a part of the tile surface is flat. (Surface the face or back of a tile. Measurements are made along the
trim tile should be treated as flat tile whenever possible.) edges of a tile or along the diagonals, or both. The deviation is
1.1.6 Square or Oblong Tile with facial area less than 4 expressed as convex or concave warpage in relation to the tile
in.2 (26 cm2) and at least two straight sides equal to or greater face, and its magnitude is calculated as a percentage of the
than 1.0 in. (25 mm) long. (Modular 1- by 1-in. tile are not in length of the edge or diagonal.
the scope of this test method.)
1.2 This test method is not applicable to tile having em- 5. Significance and Use
bossed surfaces that are not flat, or that have a combination of 5.1 This test method provides a means for determining
variable body thickness and an irregular face. whether or not a lot of ceramic tile meets the warpage
1.3 The values stated in inch-pound units are to be regarded requirements that may appear in specifications to assure
as standard. The values given in parentheses are mathematical satisfactory tile installations. In accordance with this test
conversions to SI units that are provided for information only method, warpage is calculated as a percentage of the length of
and are not considered standard. the edge or diagonal being tested. It is realized that the
1.4 This standard does not purport to address all of the percentage values based on the overall edge length, or on the
safety concerns, if any, associated with its use. It is the overall diagonal length of a tile will be slightly lower than
responsibility of the user of this standard to establish appro- those based on the distance between reference points. How-
priate safety and health practices and determine the applica- ever, the ratio of the overall lengths to the distance between
bility of regulatory limitations prior to use. reference points will be practically constant for any particular

2
For referenced ASTM standards, visit the ASTM website, www.astm.org, or
1
This method is under the jurisdiction of ASTM Committee C21 on Ceramic contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM
Whitewares and Related Products and is the direct responsibility of Subcommittee Standards volume information, refer to the standard’s Document Summary page on
C21.06 on Ceramic Tile. the ASTM website.
3
Current edition approved Jan. 1, 2009. Published January 2009. Originally Three drawings showing construction details are available from ASTM
approved in 1961. Last previous edition approved in 2003 as C 485 – 83 (2003)´1. Headquarters. Order ADJC0485.

Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.

Copyright by ASTM Int'l (all rights reserved); Thu Apr 16 06:29:55 EDT 2009 1
Downloaded/printed by
Laurentian University pursuant to License Agreement. No further reproductions authorized.
 C 485 – 09
size of tile and, therefore, the percentage values will be spaced apart 3⁄4 in. (19 mm) less than the length of the edge or
comparable and equally indicative of warpage. diagonal being tested, and a dial indicator tip midway between
the stationary pins and in line with them. The pins and the dial
indicator are mounted firmly on the same rigid metal bar. The
pins may have a hemispherical tip, as described in 6.2.2, or
they may be conical to a point. A more versatile apparatus for
standard sizes of tile consists of a metal plate having three
movable reference pins, three movable registry stops, and the
necessary number of dial indicators. See Fig. 1 and Fig. 2.
6.2 Apparatus for Square Tile:3
6.2.1 Metal Plate—A flat metal plate, 6 by 6 in. (152 by 152
mm) square and 1⁄4 in. (6.4 mm) thick, with a 7⁄16-in. (11-mm)
wide slot starting at the midpoint of one side and running at
right angles to that side for a distance of 25⁄8 in. (67 mm)
toward the center of the plate. The plate also has a 7⁄16-in.
diameter hole in the exact center of the plate. One side of the
plate has two 1⁄8-in. (3.2-mm) thick, 1⁄2-in. (13-mm) wide, and
1-in. (25-mm) high projections, located not more than 1⁄2 in.
from the corners, and a similar projection located on an
adjacent side and not more than 1⁄2 in. from one of the corners
of the first side. These projections serve as permanent registry
stops for 6- by 6-in. tile during measurement.
6.2.1.1 In addition, the plate has a series of tapped holes for
insertion of removable reference pins and removable registry
stops. The centers of the holes for the reference pins are located
for each nominal size of tile near three of its corners, 3⁄8 in. (9.5
FIG. 1 Apparatus for Square Tile, Set Up for Measurement of 41⁄4- mm) in from each side, when the tile is centered on the plate,
by 41⁄4-in. (108- by 108-mm) Tile except that for 2- by 2-in. (51- by 51-mm) tile the distance in
from the edges is 1⁄4 in. (6.4 mm). To receive the three registry
stops, the centers of two holes are located for each nominal size
of tile 1⁄2 in. (13 mm) from the corners of one side and 1⁄8 in.
(3.2 mm) from the edge of the tile, while the center of a third
hole is located on an adjacent side, 1⁄2 in. from one of the
corners of the first side and 1⁄8 in. from the edge of the tile.
6.2.2 Reference Pins—Three movable reference pins 5⁄8 in.
(16 mm) high and 1⁄4 in. (6.4 mm) in diameter, with the free end
ground to a hemispherical tip and the other end threaded for a
distance of 1⁄4 in. The reference pins are inserted in the metal
plate to support the tile during measurement.
6.2.3 Registry Stops—Three 1⁄4-in. (6.4-mm) diameter and
11⁄4-in. (32-mm) high, movable, flat top registry stops with a
1⁄16-in. (1.6-mm) wide and 1⁄8-in. (3.2-mm) deep slot on one

end for the insertion of a screwdriver and threaded on the other

end for a distance of 1⁄4 in. The registry stops are inserted in the
metal plate to fix the horizontal position of the tile during
measurement.
6.2.4 Dial Indicators—Two adjustable dial indicators, read-
ing in 0.001-in. (0.025-mm) increments and accurate to
60.001 in. One is inserted from the bottom through the 7⁄16-in.
(11-mm) hole in the center of the plate, permanently fastened
FIG. 2 Apparatus as Shown in Fig. 1, Showing Arrangement of to the underside of the metal plate, and used for measuring
Stem Extender
diagonal warpage. The other is inserted into the slot in the plate
and fastened in any one of four positions which represent
6. Apparatus midpoints between reference pins on one side of each of the
6.1 General Apparatus—The size and arrangement of the different nominal sizes of tile. This dial indicator is used for
apparatus for measuring the warpages vary, depending on the determining edge warpage.
size and shape of the tile to be measured. In general, the 6.2.5 True Reference Plates—Four 3⁄8-in. (9.5-mm) thick
apparatus consists of two stationary pins (reference pins) plates of true plane surface, made of steel or polished glass, one

Copyright by ASTM Int'l (all rights reserved); Thu Apr 16 06:29:55 EDT 2009 2
Downloaded/printed by
Laurentian University pursuant to License Agreement. No further reproductions authorized.
 C 485 – 09
each of the same dimensions as the four nominal sizes of tile 8. Procedure
which can be measured on this apparatus. 8.1 General—For nominally square tile use the apparatus
6.3 Apparatus for Oblong Tile:3 described under 6.2. For oblong tile use the apparatus de-
6.3.1 Metal Plate—A flat rectangular metal plate 81⁄2 by 41⁄4 scribed under 6.3.
in. (216 by 108 mm) and 1⁄4 in. (6.4 mm) thick, having two 8.2 Procedure for Square Tile:
7⁄16-in. (11-mm) wide slots. One slot should start at the
8.2.1 Depending upon the size of tile to be tested, insert the
midpoint of one 41⁄4-in. side and run at right angles to that side three registry stops and the three reference pins into the proper
for a distance of 23⁄4 in. (70 mm) towards the center of the tapped holes in the metal plate and fasten them. Move and
plate. The other slot should start at the midpoint of one 81⁄2-in. fasten the adjustable dial indicator in the slot so that its tip will
side and run at right angles to that side for a distance of 13⁄4 in. fall at the midpoint between the two reference pins on the same
(45 mm) towards the center of the plate. These slots are used side. Insert the proper reference plate and adjust the two dial
for inserting the two dial indicators necessary to measure the indicators to zero reading when the reference plate rests on the
edge warpage of one long and one short dimension of the tile reference pins and is in contact with the three registry stops.
simultaneously. There is also a 7⁄16-in. hole in the exact center 8.2.2 Insert a piece of tile with its face resting upon the three
of the plate for insertion of the third dial indicator, which is reference pins and its edges in contact with the three registry
used for measuring diagonal warpage. One side of the plate has stops. Read the two dial indicators, turn the tile 90° clockwise,
two 1⁄8-in. (3.2-mm) thick, 1⁄2-in. (13-mm) wide, and 1-in. and repeat the procedure until all four sides and the two
(25-mm) high projections, located not more than 1⁄2 in. from diagonals have been measured.
the corners and a similar projection located on an adjacent side 8.3 Procedure for Oblong Tile:
and not more than 1⁄2 in. from one of the corners of the first 8.3.1 Both diagonals of oblong tile cannot be measured for
side. These projections serve as permanent registry stops for warpage without changing one of the reference pins. Depend-
81⁄2 by 41⁄4-in. tile during measurement. ing upon the size of tile to be tested, insert the three registry
6.3.1.1 In addition, the plate has a series of tapped holes for stops and the three reference pins into the proper tapped holes
insertion of movable reference pins and movable registry stops. in the metal plate and fasten them. Insert the two movable dial
indicators, one in each slot of the plate and located so that the
The center of the holes for the reference pins is located for each
stem of one is at the midpoint between reference pins of one
nominal size of tile near its four corners, 3⁄8 in. (9.5 mm) in
short dimension and the stem of the other at the midpoint
from each side, when the tile is centered on the plate. The
between reference pins of one long dimension. Using the
centers of two of the holes to receive the three registry stops are proper reference plate so that it rests on the three reference pins
located for each size of tile 1⁄2 in. (13 mm) from the corners of and its sides are in contact with the registry stops, adjust the
one side and 1⁄8 in. (3.2 mm) from the edge of the tile, while the three dial indicators to zero reading.
center of the third hole is located on an adjacent side, 1⁄2 in.
8.3.2 Place a tile face down on the reference pins so that its
from one of the corners of the first side and 1⁄8 in. from the edges are in contact with the registry stops and read the three
edges of the tile. dial indicators. Turn the tile 180° and read the edge warpage of
6.3.2 Reference Pins—See 6.2.2. the second short and second long dimension of the tile. In order
6.3.3 Registry Stops—See 6.2.3. to determine the warpage of the second diagonal, change one
6.3.4 Dial Indicators—Three adjustable dial indicators, of the reference pins and read the warpage of the second
reading in 0.001-in. (0.025-mm) increments and accurate to diagonal, after first resetting the dial indicators to zero with the
60.001 in. One of them, used for the determination of diagonal reference plate. (In practice it will be found more expedient to
warpage, is permanently fastened on the underside of the plate, read the edge warpage and the warpage of one diagonal of all
the tile in a sample before changing the one reference pin to
with its stem projecting through the 7⁄16-in. (11-mm) hole in the
determine the warpage of the second diagonal.)
center of the plate. The other two, used for measuring edge
warpage, are inserted, one into each of the two slots in the 8.4 Procedure for Square or Oblong Tile with an Irregular
plate, and fastened in any one of the various positions Face, as defined in 1.1.3.
representing midpoints between reference pins on the same 8.4.1 Tile with an irregular face on which accurate warpage
side of the various nominal sizes of tile. Because two of the measurements can not be made must be measured on the back,
dial indicators are in one line for viewing, one of them must be if possible. If the back is also unsuitable, no warpage measure-
arranged at a different elevation than the other by using a stem ments can be made in accordance with this test method.
extender, so that both dials may be read simultaneously (Fig. 8.4.2 A suitable back may be flat, embossed with a pattern,
2). or ribbed if the following criteria are satisfied:
6.3.5 True Reference Plates—See 6.2.5. 8.4.2.1 For diagonal warpage a flat area at least 1⁄4 by 1⁄4 in.
(6.4 mm) in or near the center of the back must be in the same
nominal plane and in line with similar flat areas near the
7. Test Specimens
corners of the back. The points within these flat areas at which
7.1 At least ten tile specimens shall be selected at random the stationary points and the dial indicator tip of the apparatus
from the lot to be tested. Brush the specimens to remove all contact the tile back may be chosen with reasonable latitude,
adhering particles of clay or sand. but the same locations must be used on each tile in the sample.

Copyright by ASTM Int'l (all rights reserved); Thu Apr 16 06:29:55 EDT 2009 3
Downloaded/printed by
Laurentian University pursuant to License Agreement. No further reproductions authorized.
 C 485 – 09
8.4.2.2 For edge warpage a flat area at least 1⁄4 by 1⁄4 in. (6.4 established, it probably means the three points are not in line
mm) at the midpoint of an edge and no more than 1⁄2 in. (13 and the apparatus must be adjusted.)
mm) away from the edge must be in the same nominal plane as 8.5.4 With the tile face up on a flat work surface, measure
and in line with similar flat areas near the corners of the tile. All the deviation from a plane on an established line by placing the
three points of contact with the apparatus may be on a rib, for stationary points of the apparatus on the established points on
instance. At least two edges of the tile must be measurable for the tile surface, or evenly between them if the stationary points
warpage. are less than the ideal gage length apart. Rock the apparatus
8.4.3 Once the lines on which warpage will be measured are slowly side to side to establish a minimum reading. Record the
established, determine the gage length (distance between reading as plus (+) or minus (−) to indicate convex or concave
stationary pins on the three-point apparatus). Set the stationary curvature of the tile. Repeat the procedure for all tile in the
pins of the apparatus at a distance apart equal to the gage sample and all equal gate lengths on the tile before resetting the
length, with the tip of the dial indicator mid-way between apparatus for other gage lengths on the tile.
them. Using a true reference plate (see 6.2.5), calibrate the 8.6 Procedure for Trim Tile, as defined in 1.1.5:
apparatus to read a minimum of zero on the dial indicator when 8.6.1 This test method is applicable to the flat section or
the apparatus is held in contact with the reference plate and straight edges of trim tile when they exist.
rocked slowly from side to side on line of contact. (If no 8.6.2 Follow the procedures for the applicable paragraphs
1.1.1-1.1.4, but if extraordinary means are required, consider
minimum can be established, it probably means the three
the shape not within the scope of this test method.
points are not in line and the apparatus must be adjusted.)
8.7 Procedure for Square or Oblong Tile with Facial Area
8.4.4 With the tile back up on a flat work surface, measure Less than 4 in.2 (26 cm2) as defined in 1.1.6:
the deviation from a plane on an established line by placing the 8.7.1 Warpage measurement of small, flat tile must be
stationary points of the apparatus on the established points on performed with wire feeler gages. Only edge warpage mea-
the tile back. Rock the apparatus slowly side to side to establish surements are possible. Determine whether the front or back of
a minimum reading. Record the reading as plus (+) or minus the tile will be used to measure warpage; front is preferred
(−) to indicate convex or concave curvature of the tile (with when it is suitable. Determine the lengths of the flat portion of
respect to the tile face). Repeat the procedure for all tile in the the face along an edge. Consult the specification to find the
sample and all equal gage lengths before resetting the appara- maximum warpage allowed and choose wire feeler gages that
tus for other gage lengths on the tile. will permit go-no-go measurement. Example: if a maximum of
8.5 Procedure for Nonrectilinear Tile, as defined in 1.1.4: 0.4 % warpage is allowed and the flat portion of the edge is 1
8.5.1 Depending on the shape, and to some extent the size, in. (25 mm) long, 0.004-in. (0.10-mm) diameter wires are
of the tile to be tested, determine the lines on which warpages chosen as the feeler gage.
will be measured. A maximum of six (four edge warpages and 8.7.2 Place the tile face to be measured against the surface
two diagonal warpages) and a minimum of two warpages per of a true reference plate (see 6.2.5). If the tile does not rock on
tile are acceptable. Examples: A round tile would require two the edge being checked, try to slip the wire under the tile at the
warpages at right angles with the dial indicator tip contacting midpoint of that edge. If the wire does not fit under the tile, the
the center of the tile (diagonal warpages). A diamond-shaped tile passes. If it does fit, the tile fails. If the tile rocks on the
tile would require four edge warpages and two diagonals. A edge being checked, place one wire under the very end of the
nonrectilinear tile with no straight edges would require two edge and, holding the tile tight to that wire and the plate, try to
diagonal warpages, one on the longest face dimension and slip a second wire under the opposite end of the edge being
another at right angles to it. A triangle-shaped tile would checked. If the second wire does not fit under, the tile passes.
require three edge warpages. If it does, the tile fails.
8.5.2 If the tile have an irregular face, combine instructions 9. Calculation
from 8.4 for using the back of the tile with those for
9.1 Calculate the percentage of warpage as follows:
nonrectilinear tile.
Warpage, % 5 ~A/B! 3 100 (1)
8.5.3 Once the lines on which warpage will be measured are
established, placing lines for edge warpage 3⁄8 in. (9.5 mm) where:
away from the tile edge they parallel, determine the ideal gage A = amount of warpage in inches measured to the nearest
length (distance between stationary pins on the three-point 0.001 in. (in millimetres to the nearest 0.025 mm) and
apparatus) by establishing two points on the lines 3⁄8 in. away B = gage length, measured to nearest 1⁄16 in. (1.6 mm) plus
from the nearest tile edge or edges. Set the stationary pins of 3⁄4 in. (19 mm) and expressed in inches to the nearest

the apparatus at a distance apart equal to the ideal gage length, 0.001 in. (expressed in millimetres to the nearest 0.025
or closer than the ideal gage length by no more than 1⁄2 in. (13 mm).
mm). The tip of the dial indicator shall be exactly mid-way
between the stationary pins and in line with them. Using a true 10. Report
reference plate (see 6.2.5), calibrate the apparatus to read a 10.1 Report the following information:
minimum of zero on the dial indicator when the apparatus is 10.1.1 Nominal size of the tile tested,
held in contact with the reference plate and rocked slowly side 10.1.2 The category or categories (see 1.1.1-1.1.6) into
to side on the line of contact. (If no minimum can be which the tile were placed, and

Copyright by ASTM Int'l (all rights reserved); Thu Apr 16 06:29:55 EDT 2009 4
Downloaded/printed by
Laurentian University pursuant to License Agreement. No further reproductions authorized.
 C 485 – 09
10.1.3 Percent of warpage, either convex or concave, of 12. Keywords
each edge and diagonal tested, except in the case of tile less
12.1 ceramic tile; warpage
than 4 in.2 (26 cm2), report number of “passes” and “fails.”
11. Precision and Bias
11.1 The precision of any warpage measurement is approxi-
mately 60.05 %. Bias depends primarily on the perfection of
the true reference plate, but no interlaboratory data are avail-
able to estimate bias.

ASTM International takes no position respecting the validity of any patent rights asserted in connection with any item mentioned
in this standard. Users of this standard are expressly advised that determination of the validity of any such patent rights, and the risk
of infringement of such rights, are entirely their own responsibility.

This standard is subject to revision at any time by the responsible technical committee and must be reviewed every five years and
if not revised, either reapproved or withdrawn. Your comments are invited either for revision of this standard or for additional standards
and should be addressed to ASTM International Headquarters. Your comments will receive careful consideration at a meeting of the
responsible technical committee, which you may attend. If you feel that your comments have not received a fair hearing you should
make your views known to the ASTM Committee on Standards, at the address shown below.

This standard is copyrighted by ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959,
United States. Individual reprints (single or multiple copies) of this standard may be obtained by contacting ASTM at the above
address or at 610-832-9585 (phone), 610-832-9555 (fax), or service@astm.org (e-mail); or through the ASTM website
(www.astm.org).

Copyright by ASTM Int'l (all rights reserved); Thu Apr 16 06:29:55 EDT 2009 5
Downloaded/printed by
Laurentian University pursuant to License Agreement. No further reproductions authorized.