Designation: C952 − 12

Standard Test Method for

Bond Strength of Mortar to Masonry Units1
This standard is issued under the fixed designation C952; 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.
This standard has been approved for use by agencies of the U.S. Department of Defense.

1. Scope* C1437 Test Method for Flow of Hydraulic Cement Mortar

1.1 This test method provides two procedures for measuring E518 Test Methods for Flexural Bond Strength of Masonry
bond strength of mortar to masonry units: a crossed brick
3. Significance and Use
couplet tensile test for evaluating mortar-brick bond strength
and a stacked-bond, flexural test for evaluating mortar-concrete 3.1 These procedures are useful for research into bond
block bond strength. strength of masonry. They are not intended to predict the bond
strength of commercial masonry construction. The bond
1.2 The values stated in inch-pound units are to be regarded
strength in commercially built structures is determined by
as standard. The values given in parentheses are mathematical
many factors beyond the characteristics of mortar, masonry
conversions to SI units that are provided for information only
units, and the procedures of this test method.
and are not considered standard.
1.3 This standard does not purport to address the safety NOTE 1—The crossed-brick couplets method measures a direct tensile
strength of the bond between the mortar and masonry unit. It does not
concerns, if any, associated with its use. It is the responsibility determine the flexural strength of the unit mortar assembly. Other test
of the user of this standard to establish appropriate safety and methods may be more appropriate for determining the flexural bond
health practices and determine the applicability of regulatory strength between mortar and masonry units. These include Test Methods
limitations prior to use. C1072 and Test Methods E518.

PREPARATION AND TESTING OF FRESH MORTAR

2. Referenced Documents
2.1 ASTM Standards:2 4. Preparation of Mortar
C67 Test Methods for Sampling and Testing Brick and
4.1 Proportion mortar materials by weights equivalent to
Structural Clay Tile
volume proportions to be used in prism construction. Use unit
C90 Specification for Loadbearing Concrete Masonry Units
weights for individual materials as given in Specification
C129 Specification for Nonloadbearing Concrete Masonry
C270. Sand shall be permitted to be used in a damp loose
Units
condition, provided that moisture content of sand is determined
C140 Test Methods for Sampling and Testing Concrete
with reference to the oven-dried condition and batch propor-
Masonry Units and Related Units
tions are adjusted accordingly. Record weight of ingredients
C270 Specification for Mortar for Unit Masonry
(including water) added to the batch of mortar.
C780 Test Method for Preconstruction and Construction
Evaluation of Mortars for Plain and Reinforced Unit 4.2 Mix mortar in a mechanical paddle-type mortar mixer.
Masonry Time periods referenced below are measured from when water
C1072 Test Methods for Measurement of Masonry Flexural and cementitious materials are combined.
Bond Strength 4.2.1 Add an estimated amount of water to the mortar to
achieve the desired consistency (Note 2). Mix mortar for three
minutes and determine consistency. If the desired consistency
1
This test method is under the jurisdiction of ASTM Committee C15 on is specified by flow determine it in accordance with Test
Manufactured Masonry Units and is the direct responsibility of Subcommittee Method C1437. If the desired consistency is specified as initial
C15.04 on Research. Committee E-6 maintains a continued interest in these cone penetration, determine it in accordance with Test Method
practices and will make use of them in the future.
Current edition approved June 1, 2012. Published July 2012. Originally approved C780. Once consistency is recorded, return the material used to
in 1959. Last previous edition approved in 2009 as C952 – 02 (2009). DOI: measure the consistency to the mixer. If the consistency is
10.1520/C0952-12.
2
within the desired range, continue mixing the batch for an
For referenced ASTM standards, visit the ASTM website, www.astm.org, or
additional two minutes. If the consistency is less than the
contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM
Standards volume information, refer to the standard’s Document Summary page on desired range, add water to the batch and mix for one minute
the ASTM website. and determine consistency. Once consistency is recorded,

*A Summary of Changes section appears at the end of this standard

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

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 C952 − 12

FIG. 1 Splash Board

return the material used to measure consistency to the mixer. If 6.1.1 Bond between specified brick and a specified mortar,
the consistency is within the desired range, continue mixing the 6.1.2 Relative bond between different brick and a specified
batch for one minute. mortar, or
NOTE 2—Workable consistency of mortar for concrete masonry con- 6.1.3 Relative bond between a specified brick and different
struction generally requires an initial cone penetration reading of 55 6 5 mortars.
mm or a flow of 125 6 5 %. Workable consistency of mortar for clay 6.1.4 In each case, the initial rate of absorption of the brick
masonry construction generally requires an initial cone penetration
reading of 65 6 5 mm or a flow of 135 6 5 %. Optimum consistency for shall be determined in accordance with Test Methods C67. The
a specific mortar-unit combination may differ from these values. brick used for couplets shall include the full range of absorp-
tion rates acceptable under the specifications.
4.2.2 If after the one-time addition of water the consistency
is not in the desired range, discard the batch. 6.2 Construction of Test Specimens :
4.2.3 If the measured consistency exceeds the desired range 6.2.1 Center the mold on the lower brick of the couplet and
at any time, discard the batch. lightly mix a small quantity of mortar on the board by turning
4.3 Immediately after mixing the mortar, determine its over with the spoon.
initial cone penetration in accordance with Test Method C780. 6.2.2 Half-fill the mold by sharply dashing into each corner
Determine the cone penetration of the mortar every 15 6 5 and the center of the mold a small quantity of mortar from the
minutes. If the cone penetration is less than 80 % of its initial half-filled spoon. Note the time at start of a 1-min interval.
value, discard the remaining portion of the mortar without Apply additional mortar by heaping loosely with the spoon
constructing additional mortar joints. above the top of the mold. Strike off excess mortar with the
straightedge, starting on a diagonal across the mold and
PREPARATION AND TESTING OF BOND STRENGTH working first to one corner and then to the opposite corner of
TEST SPECIMENS the mold. Remove the mold from the mortar bed.
5. Apparatus 6.2.3 At the end of the 1-min time interval, place the upper
brick on the mortar bed in a crosswise direction to the lower
5.1 Miscellaneous— Brass-covered mortar board 18 in.
brick. Place the frame of the hammer on the top brick with the
(457 mm) square, an 11-in. (279-mm) long mason’s trowel,
weight of the hammer held in the other hand. Drop the hammer
laboratory trowel with straight edges, short handled spoon or
in a frame a distance of 11⁄2 in. (38 mm).
scoop of 1⁄4-cup (0.5-dm 3) capacity, steel straightedge 10 in.
(254 mm) long, metal mold 1⁄2 in. (13 mm) deep with 35⁄8-in. 6.2.4 Measure and record the extrusion of the mortar on the
(92-mm) square opening beveled to slope of 0.08 (total 0.04), top surface of the lower brick. Cut away extruded mortar from
splash board (Fig. 1) with handle 20 in. (508 mm) long and 3 all four edges of the mortar bed.
in. (76 mm) wide. 6.3 Curing—Promptly enclose the test specimen within an
5.2 Drop Hammer for crossed-brick couplets (Fig. 2, Table airtight covering. Keep covered for 7 days. Remove the cover
1). and store until tested. Unless otherwise specified, the specimen
shall be stored in laboratory air at a relative humidity of at least
5.3 Drop Hammer for block assemblies (Fig. 3). 50 %.
5.4 Loading Jigs for crossed-brick couplets (Fig. 4).
6.4 Testing—Center the specimen between the upper and
5.5 Frames (Fig. 5) for testing block assemblies: upper lower tripods and place in the testing machine as shown in Fig.
frame fitted with ball bearing mounted 10 in. (254 mm) from 6. Load the specimen at the rate of 600 lb (2.7 kN)/min or at
vertical axis of specimen for eccentric application of vertical a rate sufficient to cause failure in 1 to 2 min. Note and record
load. . maximum load and type of failure.
5.6 Torque Wrench. NOTE 3—The method of making the specimens typically produces a
6. Crossed-Brick Couplets failure of the joint at the top of the mortar bed.
NOTE 4—Reproducibility of test results may be improved by the
6.1 Brick—Test specimens consisting of crossed-brick cou- insertion of strips of high-density insulation board interlayers between the
plets may be used to determine: test specimen and test apparatus.

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 C952 − 12

FIG. 2 Drop Hammer for Cross-Brick Couplets

TABLE 1 Metric Equivalents for Figs. 2, 3, 4, 5, and 6

Inch-Pound Metric Inch-Pound Metric Inch-Pound Metric
⁄
1 16 in. 1.6 mm 13⁄4 in. 44 mm 5 in. 127 mm
1⁄8 in. 3 mm 17⁄8 in. 48 mm 51⁄4 in. 133 mm
3⁄16 in. 4.7 mm 2 in. 51 mm 53⁄4 in. 146 mm
1⁄4 in. 6.4 mm 21⁄8 in. 54 mm 6 in. 152 mm
3⁄8 in. 9.5 mm 21⁄4 in. 57 mm 61⁄4 159 mm
7⁄16 in. 11 mm 23⁄8 in. 61 mm 71⁄2 in. 190 mm
1⁄2 in. 12.7 mm 21⁄2 in. 64 mm 8 in. 203 mm
5⁄8 in. 15.8 mm 25⁄8 in. 67 mm 81⁄2 in. 216 mm
3⁄4 in. 19 mm 3 in. 76 mm 93⁄4 in. 248 mm
7⁄8 in. 22 mm 31⁄8 in. 79 mm 103⁄4 in. 273 mm
1 in. 25 mm 31⁄4 in. 82 mm 16 in. 406 mm
11⁄8 in. 28 mm 31⁄2 in. 89 mm 161⁄2 in. 419 mm
1 ⁄16 in.
3 30 mm 35⁄8 in. 92 mm 183⁄4 in. 476 mm
11⁄4 in. 32 mm 33⁄4 in. 95 mm 28 in. 711 mm
13⁄8 in. 35 mm 4 in. 102 mm 2 lb 0.9 kg
11⁄2 in. 38 mm 43⁄4 in. 121 mm 3.5 lb 1.6 kg

6.5 Calculation— Calculate the maximum tensile bond 7. Concrete Masonry Unit Assemblies
strength as follows:
7.1 Concrete Masonry Units—Concrete masonry units used
Tensile bond strength, T, psi ~ or N/m 2 ! 5 A/B (1) in test specimens shall conform to Specification C90 or C129.
where: The moisture content of the concrete masonry units shall be as
A = total applied load, lbf (or N), and specified. In the absence of any other specified moisture
B = cross-sectional area in bond, in.2 (or m2). content, the concrete masonry units shall be conditioned to

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 C952 − 12

FIG. 3 Drop Hammer for Concrete Block Assemblies

FIG. 4 Loading Jigs for Crossed-Brick Couplets

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 C952 − 12

FIG. 5 Frames for Testing Concrete Block Assemblies

FIG. 5 Frames for Testing Concrete Block Assemblies (continued)

have a moisture content of between 25 % and 35 % of total 7.2 Construction of Test Specimens :
absorption, as determined in accordance with Test Methods 7.2.1 Position the bottom concrete masonry unit of the
C140. assembly on a metal pallet with the thickest part of the face

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 C952 − 12

FIG. 6 Crossed-Brick Test Assembly Positioned in Testing Machine

shells upwards. Lightly turn over and remix the mortar on the until tested. Unless otherwise specified, the specimen shall be
board with a mason’s trowel. stored in laboratory air at a relative humidity of at least 50 %.
7.2.2 With a mason’s trowel and technique, apply mortar to
7.4 Testing—Clamp the specimen in the lower and upper
the top of the face shell that will be in the compressive face of
test frames by tightening the screws of the test frames with a
the specimen, when tested. The amount of mortar applied shall
torque wrench (see Fig. 8). Center the ball bearing on the upper
be sufficient to produce a bed joint of the desired thickness in
test frame in the testing machine. Apply a vertical load to the
the finished specimen (Note 5). In the absence of any specified
thickness, the bed joints in the finished specimen shall be of a specimen at the rate of 600 lbf (2.7 kN)/min or at a rate
nominal 3⁄8-in. (9.5-mm) thickness. sufficient to cause failure in 1 to 2 min.

NOTE 5—The consistency of the mortar, when made, and the amount of 7.5 Calculation— Calculate the maximum flexural bond
water used in the mortar shall have been adjusted to meet the requirements strength of the section for the gross and the net section of the
for the proper joint thickness of concrete masonry unit assemblies. specimen, taken normal to the face shells, as follows:
7.2.3 Hold the splash board along the top of the opposite f g 5 ~ xPc/I g ! 2 ~ P/A g ! (2)
face shell (the shell that will be in the tensile face of the
specimen) and with the mason’s trowel lightly loaded, sharply f n 5 ~ xPc/I n ! 2 ~ P/A n !
dash a thin bed of mortar on the top of this shell as shown in where:
Fig. 7. Remove the splash board. Note the time for the start of
fg = flexural bond stress on gross area, psi (or N/m2)
a 1-min interval. Load the trowel and build up the mortar bed fn = flexural bond stress on net area, psi (or N/m2),
by gently rolling or dropping a sufficient amount of additional x = lever arm of load about vertical axis of specimen, in.
mortar. (or m),
7.2.4 At the end of the 1-min time interval, pick up and level P = applied load, lbf (or N),
the upper concrete masonry unit of the assembly on the mortar c = distance from neutral axis to face of specimen, in. (or
beds by bringing the concrete masonry unit downward and m),
forward to one end of the lower masonry unit. The upper Ig = moment of inertia of gross section, in.4 (or m4),
concrete masonry unit shall be placed with the thin edge of the In = moment of inertia of net section, in.4 (or m4),
face shells in the mortar. b = length of masonry unit, in. (or m),
7.2.5 Immediately position the drop hammer frame at the d = width of masonry unit, in. (or m),
center of the upper masonry unit, holding the weight of the t = minimum thickness of face shell, in. (or m),
hammer in the other hand. Drop the hammer in the tubular Ag = gross area of section = bd, in.2 (or m2), and
frame a distance of 4 in. (102 mm). Remove the drop hammer. An = net area of section = 2bt, in.2 (or m2).
No further adjustment of the top masonry unit on its bed shall
be made. 8. Precision and Bias
7.2.6 Measure and record the extrusion of mortar from the 8.1 Variability is a characteristic of tensile and flexural bond
faces of the specimen. Cut extruded mortar away with the stresses. Round robin testing has not been performed on these
mason’s trowel. Tool the joints with a rounded iron. methods. Coefficients of variation of 15 to 35 % are common-
7.3 Curing—Promptly enclose the specimen in an airtight place in published investigations using the methods of this
covering. Keep covered for 7 days. Remove the cover and store standard.

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 C952 − 12

FIG. 7 Preparing Concrete Block Test Assembly

FIG. 8 Concrete Block Test Assembly Positioned in Testing Machine

9. Keywords
9.1 bond; concrete masonry unit; crossed brick couplet;
mortar; masonry

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 C952 − 12
SUMMARY OF CHANGES

Committee C15 has identified the location of selected changes to this standard since the last issue
(C952 – 02(2009)) that may impact the use of this standard. (Approved June 1, 2012.)

(1) Changes have been made to subsection 2.1 and Note 1 to

remove the reference to Test Methods C1357 since the provi-
sions in Test Methods C1357 have been incorporated into Test
Methods C1072.

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