ASTM D7234-05
(Test Method)Standard Test Method for Pull-Off Adhesion Strength of Coatings on Concrete Using Portable Pull-Off Adhesion Testers
Standard Test Method for Pull-Off Adhesion Strength of Coatings on Concrete Using Portable Pull-Off Adhesion Testers
SIGNIFICANCE AND USE
The pull-off adhesion strength and mode of failure of a coating from a concrete substrate are important performance properties that are used in specifications. This test method serves as a means for uniformly preparing and testing coated surfaces, and evaluating and reporting the results.
Variations in strength results obtained using different instruments, different substrates, or different loading fixtures with the same coating are possible. Therefore, it is recommended that the specific test instrument and loading fixture be mutually agreed upon between the interested parties.
This test method should not be used to determine surface strength of uncoated concrete. Test Method C 1583/C 1583M is suitable for that determination.
SCOPE
1.1 This test method covers procedures for evaluating the pull-off adhesion strength of a coating on concrete. The test determines the greatest perpendicular force (in tension) that a surface area can bear before a plug of material is detached. Failure will occur along the weakest plane within the system comprised of the test fixture, adhesive, coating system, and substrate, and will be exposed by the fracture surface.
1.2 This test method uses a class of apparatus known as portable pull-off adhesion testers. They are capable of applying a concentric load and counter load to a single surface so that coatings can be tested even though only one side is accessible. Measurements are limited by the strength of adhesion bonds between the loading fixture, coating system and the substrate or the cohesive strengths of the adhesive, coating layers, and substrate.
1.3 Pull-off adhesion strength measurements depend upon both material and instrumental parameters. There are different instruments used that comply with this test method. The specific instrument used should be identified when reporting results. This test is destructive and spot repairs may be necessary.
1.4 The values stated in SI units are to be regarded as the standard. The values given in parentheses are for information only.
This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use.
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Standards Content (Sample)
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Designation: D7234 − 05
StandardTest Method for
Pull-Off Adhesion Strength of Coatings on Concrete Using
Portable Pull-Off Adhesion Testers
This standard is issued under the fixed designation D7234; 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 evaluating the 2.1 ASTM Standards:
pull-off adhesion strength of a coating on concrete. The test C1583 Test Method for Tensile Strength of Concrete Sur-
determines the greatest perpendicular force (in tension) that a faces and the Bond Strength or Tensile Strength of
surface area can bear before a plug of material is detached. Concrete Repair and Overlay Materials by Direct Tension
Failure will occur along the weakest plane within the system (Pull-off Method)
comprised of the test fixture, adhesive, coating system, and D16 TerminologyforPaint,RelatedCoatings,Materials,and
substrate, and will be exposed by the fracture surface. Applications
D2651 GuideforPreparationofMetalSurfacesforAdhesive
1.2 This test method uses a class of apparatus known as
2 Bonding
portable pull-off adhesion testers. They are capable of apply-
D3933 Guide for Preparation of Aluminum Surfaces for
ing a concentric load and counter load to a single surface so
Structural Adhesives Bonding (Phosphoric Acid Anodiz-
that coatings can be tested even though only one side is
ing)
accessible. Measurements are limited by the strength of adhe-
D4541 Test Method for Pull-Off Strength of Coatings Using
sion bonds between the loading fixture, coating system and the
Portable Adhesion Testers
substrate or the cohesive strengths of the adhesive, coating
E178 Practice for Dealing With Outlying Observations
layers, and substrate.
3. Terminology
1.3 Pull-off adhesion strength measurements depend upon
both material and instrumental parameters. There are different
3.1 The terms and definitions in Terminology D16 apply to
instruments used that comply with this test method. The
this test method.
specific instrument used should be identified when reporting
3.2 Definitions:
results. This test is destructive and spot repairs may be
3.2.1 adhesive, n—(with respect to this test method) adhe-
necessary.
sive refers to the material that bonds the bottom of the loading
1.4 The values stated in SI units are to be regarded as the
fixture to the top surface of the coating to be tested.
standard. The values given in parentheses are for information
3.2.2 loading fixture, n—(also referred to as dolliesorstuds)
only.
a metal structure that is flat on one end for bonding to the
1.5 This standard does not purport to address all of the
coating surface and shaped on the other end for attachment to
safety concerns, if any, associated with its use. It is the
the adhesion tester and is used to determine the pull-off
responsibility of the user of this standard to establish appro-
adhesion strength of coatings
priate safety and health practices and determine the applica-
3.2.3 portable pull-off adhesion testers, n—instruments that
bility of regulatory limitations prior to use.
are capable of applying a concentric load and counter load to
asinglesurfacesothatcoatingscanbetestedeventhoughonly
This test method is under the jurisdiction of ASTM Committee D01 on Paint
one side is accessible.
and Related Coatings, Materials, andApplications and is the direct responsibility of
Subcommittee D01.46 on Industrial Protective Coatingss.
Current edition approved Dec. 1, 2005. Published February 2006. DOI: 10.1520/ For referenced ASTM standards, visit the ASTM website, www.astm.org, or
D7234-05. contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM
The term adhesion tester may be somewhat of a misnomer, but its adoption by Standards volume information, refer to the standard’s Document Summary page on
two manufacturers and at least two patents indicates continued usage. the ASTM website.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
D7234 − 05
4. Summary of Test Method 6.1.5 Force Indicator and Calibration Information, for
determining the actual force delivered to the loading fixture.
4.1 The general pull-off adhesion test is performed by
The force indicator shall be verified to be within +/-5 % of the
scoring through the coating down to the surface of the concrete
force measured by a calibrated testing machine at a frequency
substrate at a diameter equal to the diameter of the loading
determined by the user, typically once a year.
fixture (dolly, stud), and securing the loading fixture normal
(perpendicular) to the surface of the coating with an adhesive. 6.2 Timer, or means of limiting the rate of stress to less than
After the adhesive is cured, a testing apparatus is attached to 0.2 MPa/s (30 psi/s) so that the maximum stress (failure) is
the loading fixture and aligned to apply tension normal to the obtained in about 5 to 30 s.
test surface. The force applied to the loading fixture is then
6.3 Solvent, or other means for cleaning the loading fixture
uniformly increased and monitored until a plug of material is
surface.
detached. When a plug of material is detached, the exposed
6.4 Fine Sandpaper,orothermeansofcleaningorpreparing
surface represents the plane of limiting strength within the
the coating that will not alter its integrity.
system.Thenatureofthefailureisqualifiedinaccordancewith
the percent of adhesive and cohesive failures, and the actual 6.5 Adhesive,forsecuringthefixturetothecoatingthatdoes
interfacesandlayersinvolved.Thepull-offadhesionstrengthis not affect the coating properties. Two-component epoxies and
computed based on the maximum indicated load, the instru-
acrylics have been found to be the most versatile.
ment calibration data, and the surface area stressed. Pull-off
6.6 Mechanical Clamps, if needed, for holding the fixture in
adhesion strength results obtained using different devices may
place while the adhesive cures.
be different because the results depend on instrumental param-
6.7 Cotton Swabs, or other means for removing excess
eters.
adhesive.
5. Significance and Use 6.8 Core Bit with Drill Press or Hand Drill, and means to
ensure that the scoring is normal to the coating for the
5.1 The pull-off adhesion strength and mode of failure of a
procedures that use a round loading fixture. The core bit inside
coating from a concrete substrate are important performance
diameter should equal the diameter of the loading fixture. If a
properties that are used in specifications. This test method
core bit with an inside diameter equal to the diameter of the
serves as a means for uniformly preparing and testing coated
loadingfixtureisnotavailable,theclosestsizeavailableshould
surfaces, and evaluating and reporting the results.
be used. The core bit or saw blades should be diamond tipped
5.2 Variations in strength results obtained using different
and, when required to minimize heat and suppress dust,
instruments, different substrates, or different loading fixtures
supplemented with water lubrication. For the test procedures
with the same coating are possible. Therefore, it is recom-
that use a square or rectangular loading fixture, a circular saw
mended that the specific test instrument and loading fixture be
is required instead of a core bit and drill. Alternately, for thin
mutually agreed upon between the interested parties.
or elastomeric coatings, a sharp knife or hole saw may be
5.3 This test method should not be used to determine sufficient to score around the loading fixture.
surface strength of uncoated concrete. Test Method C1583 is
suitable for that determination. 7. Test Preparation
7.1 Themethodforselectingthecoatingsitestobeprepared
6. Apparatus
for testing depends upon the objectives of the test and
agreements between the contracting parties. There are, how-
6.1 Adhesion Tester, including the components and accesso-
ries described in 6.1.1-6.1.5 ever,afewphysicalrestrictionsimposedbythegeneralmethod
and apparatus. The following requirements apply to all sites:
6.1.1 Loading Fixtures,havingaflatsurfaceononeendthat
7.1.1 The selected test area must be a flat surface large
can be adhered to the coating and a means of attachment to the
enoughtoaccommodatethespecifiednumberofreplicatetests.
tester on the other end. The bonding surface may be round,
The surface may have any orientation with reference to
squareorrectangular.Theroundloadingfixturesareusually50
gravitational pull. Each test site must be separated by at least
mm (2.0 in) in diameter but may range from 20 mm (0.75 in)
the distance needed to accommodate the detaching apparatus.
to 75 mm (3.0 in) in diameter.
The size of a test site is essentially that of the secured loading
6.1.2 Detaching Assembly, having a central grip for engag-
fixture. At least three replications are required in order to
ing the loading fixture.
statistically characterize the test area.
6.1.3 Base, on the detaching assembly, for uniformly press-
7.1.2 The selected test areas must also have enough perpen-
ing against the coating surface around the fixture either
dicularandradialclearancetoaccommodatetheapparatus,and
directly, or by way of an intermediate bearing ring.Ameans of
aligning the base is needed so that the resultant force is normal
to the surface.
6.1.4 Force Applicator, means of moving the grip away
The sole source of supply of the acrylics known to the committee at this time
is Versiloc 201 and 204 with accelerator, available from Lord Corp., Industrial
from the base in as smooth and continuous a manner as
Adhesive Div., 2000 W. Grandview Blvd., P.O. Box 10038, Erie, PA 16514. If you
possible so that a torsion free, co-axial (opposing pull of the
are aware of alternative suppliers, please provide this information to ASTM
grip and push of the base along the same axis) force results
International Headquarters. Your comments will receive careful consideration at a
between them. meeting of the responsible technical committee, which you may attend.
D7234 − 05
be flat enough to permit alignment. It should be noted that fixture or the surface to be tested, or both, using a method
measurementsclosetoanedgemaynotberepresentativeofthe recommended by the adhesive manufacturer. Be certain to
coating as a whole.
apply the adhesive across the entire surface. Position fixture on
the surface to be tested centered directly over the scored
7.2 Scoring the coating down to the surface of the substrate
section with the fixture outer sides lined up with the inside
is required for all coatings thicker than 0.5 mm (20 mils) and
circumference of the scored section. Carefully remove the
for all reinforced or elastomeric coatings. While scoring is
excess adhesive from around the fixture. (Warning—
recommended for coatings thinner than 0.5 mm (20 mils), the
Movement, especially twisting, can cause tiny bubbles to
test may be performed without scoring, but the results should
coalesce into large holidays that constitute stress discontinui-
note this exception. Scoring shall be performed in a manner
ties during testing.)
that ensures the cut is made normal to the coating surface and
in a manner that does not twist or torque the test area and
NOTE 2—Adding about 1 percent of #5 glass beads to the adhesive
minimizes heat generated and edge damage or microcracks to
assists in even alignment of the test fixture to the surface.
the coating and the concrete substrate. For thick coatings it is
7.5 Basedontheadhesivemanufacturer’srecommendations
recommended to cool the coating and substrate during the
and the anticipated environmental conditions, allow enough
cutting process with water lubrication. When using a round
time for the adhesive to set up and reach the recommended
loading fixture, scoring is performed before the loading fixture
cure. During the adhesive set and early cure stage, a constant
is attached (see Fig. 1). When using square or rectangular
contact pressure should be maintained on the fixture. Mechani-
loading fixtures, scoring is typically performed after the
cal clamping systems work well, but systems relying on tack,
loading fixture is attached (see Fig. 2).
such as masking tape, should be used with care to ensure that
7.3 Clean the surfaces in a manner that will not affect
theydonotrelaxwithtimeandallowairtointrudebetweenthe
integrity of the coating or leave a residue. Clean the loading
fixture and the test area.
fixture surface as indicated by the apparatus manufacturer.
7.6 Note the temperature and relative humidity during the
Failures at the fixture-adhesive interface can often be avoided
time of test.
by treating the fixture surfaces in accordance with an appro-
priateASTM standard practice for preparing metal surfaces for
adhesivebonding.Fingerprints,moisture,andoxidestendtobe 8. Test Procedure
the primary contaminants.
8.1 Select an adhesion-tester having a force calibration
NOTE 1—Guides D2651 and D3933 are typical of well-proven methods
spanning the range of expected values along with its compat-
for improving adhesive bond strengths to metal surfaces.
ible loading fixture. Mid-range measurements are usually the
7.4 Prepare the adhesive in accordance with the adhesive best, but read the manufacturer’s operating instructions before
manufacturer’s recommendations. Apply the adhesive to the proceeding.
FIG. 1 Scoring Around the Loading Fixture Prior to Attachment of the Fixture (Round Loading Fixtures)
D7234 − 05
FIG. 2 Scoring Around the Loading Fixture After Attachment of the Fixture (Square or Rectangular Fixtures)
8.2 If a bearing ring or comparable device is to be used, 9.2 Either use the calibration chart supplied by the manu-
placeitconcentricallyaroundtheloadingfixtureonthecoating facturer or compute the relative stress applied to each coating
surface. If shims are required when a bearing ring is employed, sample as follows:
place them between the tester base and bearing ring rather than
4F
X 5 (1)
on the coating surface. 2
πd
8.3 Carefully connect the central grip of the detaching
where:
assembly to the loading fixture without bumping, bending, or
X = pull-off adhesion strength achieved at failure in MPa
otherwise prestressing the sample and connect the detaching
(psi).
assembly to its control mechanism, if necessary. For nonhori-
F = Maximum force applied to the test surface at failure and
zontal surfaces, support the detaching assembly so that its
as determined in 9.1 in N(lb) ,
...
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