Coating Adhesion Testing Methods and Equipment Webinar Content:
Why Measure Adhesion Properties? What is Being Measured? Selecting
an Adhesion Testing Method Measuring Adhesion by the Tape Test
Measuring Adhesion by the Knife Test Measuring Pull-off Adhesion
Fixed Alignment Mechanical Self-Aligning Hydraulic (3 devices) Self
Aligning Pneumatic Special Requirements for Testing Concrete
Coating Adhesion Common Pitfalls When Testing Coating Adhesion
Reporting
Slide 3
Learning Outcomes Completion of this webinar will enable the
participant to: Explain the purpose of testing the adhesion
properties of coatings Describe the two types of adhesion testing
mechanisms List four standard test methods used to test the
adhesion of coating systems Describe the difference between shear
adhesion and tensile adhesion Measure the adhesion of coating
systems using the tape method Measure the adhesion of coating
systems using the knife method
Slide 4
Learning Outcomes, continued Describe the difference between
fixed alignment and self aligning adhesion testers Explain the
differences between testing the pull-off strength of coatings
applied to steel and concrete surfaces Measure the tensile
(pull-off) strength of coating systems using mechanical, hydraulic
and pneumatically-operated testing devices List common pitfalls
associated with adhesion testing of coatings Evaluate potential
locations of break, including adhesion, cohesion and glue Describe
the reporting requirements for adhesion testing
Slide 5
Why Measure Adhesion Properties? Determine specification
compliance Common in-process inspection of TSC Determine
maintenance strategy for existing coating systems Adhesion data is
not typically a predictor of coating performance
Slide 6
What is Being Measured? Measuring Coating Strength at Different
Planes Adhesion Strength Bond strength between the substrate and
the coating and/or the coating layers to one another Cohesion
Strength Inner-strength of a coating layer Adhesion strength is
highly variable No industry-wide adhesion acceptance value Minimum
adhesion values may be on a PDS or in a specification
Slide 7
Selecting a Test Method ASTM StandardMethod D 3359-09Adhesion
By Tape Test D 6677-07Knife Adhesion D 4541-09Pull-off Strength of
Coatings Using Portable Adhesion Testers D 7234-05Pull-off Strength
of Coatings on Concrete Using Portable Pull-off Adhesion
Testers
Slide 8
Selecting a Test Method Tape and Knife Adhesion require minimal
equipment and can be conducted quickly Evaluate shear or peel
strength (peel-back) Pull-off adhesion requires specialized
equipment and the testing takes comparatively longer to perform
Evaluates pull-off strength (resistance to perpendicular pull)
Cannot compare data, since testing mechanisms are different
Adhesion testing is destructive to the coating film
Slide 9
Measuring Adhesion By Tape Test Equipment Steel ruler or guide
Utility knife Brush Adhesive tape Magnifier ASTM Test Method
Cross-cut Tester (alternative to knife and guide)
Slide 10
Measuring Adhesion By Tape Test Step 1: Select test area(s) and
conduct triplicate tests per area Step 2: Determine the thickness
of the coating system Step 3: Select the test method based on the
coating thickness Method A (X-cut): Coating thickness > 5 mils
Method B (Cross-cut): Coating thickness < 5 mils Up to 2 mils:
Use 1mm spacing between incisions (11 cuts) From 2-5 mils: Use 2mm
spacing between incisions (6 cuts)
Slide 11
Measuring Adhesion By Tape Test Method A (X-cut) Make a single
1.5 cut through the coating system. Avoid multiple passes. Make a
second cut to form an X 30-45 angle at intersection of the X
Slide 12
Measuring Adhesion By Tape Test Method A (X-cut) Remove cutting
debris Remove 2 laps of tape (discard) Apply 3 piece of tape to
X-cut Cover all of X-cut Assure good tape contact Remove tape
within 90 +/- 30 seconds Remove tape 180 back across X-cut (do not
pull upwards)
Slide 13
Measuring Adhesion By Tape Test Method A (X-cut)
RatingDescription 5ANo peeling or removal 4ATrace peeling or
removal along the incisions 3AJagged removal along the incisions up
to 1/16 on either side 2AJagged removal along the incisions up to
1/8 on either side 1ARemoval of most of the coating from the area
of the X under the tape 0ARemoval of coating beyond the area of the
X
Slide 14
Measuring Adhesion By Tape Test Method B (Cross-cut) Make
series of 6 or 11 parallel incisions through the coating system.
Avoid multiple passes. Make a second series of incisions
perpendicular to first series
Slide 15
Measuring Adhesion By Tape Test Method B (Cross-cut) Remove
cutting debris Remove 2 laps of tape (discard) Apply 3 piece of
tape to grid Cover all of grid Assure good tape contact Remove tape
within 90 +/- 30 seconds Remove tape 180 back across cross-cut (do
not pull upwards)
Slide 16
Measuring Adhesion By Tape Test Method B (Cross-cut)
Rating%Description 5B0%Edges of cuts completely smooth 4B65%Flaking
& detaching worse than 1B
Slide 17
Measuring Adhesion By Knife Test Equipment Steel ruler or guide
Utility knife ASTM Test Method
Slide 18
Measuring Adhesion By Knife Test Select test area Make a single
1.5 cut through the coating system. Avoid multiple passes. Make a
second cut to form an X 30-45 angle at intersection of the X
Attempt to lift coating with tip of knife blade
Slide 19
Measuring Adhesion By Knife Test RatingDescription 10 Coating
is extremely difficult to remove. Fragments no larger than 1/32 x
1/32 removed with great difficulty 8 Coating is difficult to
remove. Coating chips from 1/16 x 1/16 to 1/8 x 1/8 removed with
difficulty 6 Coating is somewhat difficult to remove. Coating chips
from 1/8 x 1/8 to 1/4 x 1/4 removed with slight difficulty 4
Coating is somewhat difficult to remove. Coating chips in excess of
1/4 x 1/4 removed using light pressure with knife blade 2 Coating
is easy to remove. Once started with the knife blade, the coating
can be grasped with fingers and easily peeled to a length of at
least 1/4 0 Coating is easy to remove. Once started with the knife
blade, the coating can be grasped with fingers and easily peeled to
a length greater than 1/4
Slide 20
Pitfalls to Avoid ASTM D3359 is for coatings on metallic
surfaces Dull knife blades can produce erroneous results Maintain
proper spacing between incisions when employing the cross-cut tape
adhesion method When employing the X-cut methods (tape or knife
adhesion procedures), maintain proper angle at intersection of X.
The legs of the X should be ~ 1 apart (width of adhesive tape)
Report tape used. Store tape properly Tape may not be effective in
cold temperatures
Slide 21
What Tape Should be Used? Note 5 in the current standard lists
Permacel 99 as suitable Permacel 99 discontinued in 2009 No
immediate replacement Intertape Polymer Group LA26 will be
investigated (backing, adhesive, thickness & adhesion to steel
similar) Section 5.3 indicates 1 (25 mm) width and adhesion
strength as agreed is acceptable Exercise caution when comparing
data using different tapes/batches of tape
Slide 22
Reporting Substrate type and coating system; method of cure
Environmental conditions (temperature and RH) No. of tests
performed Manufacturer and type of tape employed (when used) Mean
and range of ratings Location of Break (between coats, within a
coat, between substrate surface and primer, etc.)
Slide 23
Measuring Pull-off Adhesion ASTM D4541, Pull-off Strength of
Coatings Using Portable Adhesion Testers Annex A1: Fixed Alignment
Type II (mechanical) Annex A2: Self Aligning Type III (hydraulic)
Annex A3: Self Aligning Type IV (pneumatic) Annex A4: Self Aligning
Type V( hydraulic) Annex A5: Self Aligning Type VI (hydraulic)
Note: Different testers may yield different pull-off values
Slide 24
Preparing the Test Surfaces Remove dirt, chalking, oil or other
interfering materials Lightly roughen smooth or glossy surfaces
using fine grit paper or abrasive pad Remove any residual dust
using a compatible solvent
Slide 25
Loading Fixture Design Fixed Alignment Type II Self-Aligning
Type III Self-Aligning Type VI Self-Aligning Type V Self-Aligning
Type IV
Slide 26
Preparing the Loading Fixtures Loading fixtures for Type II and
Type IV testers are available pre-abraded Loading fixtures for
other testers may need to be abraded to enhance bond to surface
(recommended) Clean fixtures before use
Slide 27
Selecting an Adhesive High solids epoxy adhesives Cyanoacrylate
adhesive Ensure compatibility with coating UV curable adhesive
available with Type IV tester (requires special loading fixtures
with transparent base)
Slide 28
Attaching the Loading Fixtures Apply adhesive to the loading
fixture, surface, or both Addition of No. 5 glass beads (1%)
assists with fixture alignment Attach the loading fixture to the
coated surfaces Push downward; do not twist Remove excess
adhesive
Slide 29
Attaching the Loading Fixtures (Type III Tester) Insert Teflon
plug Apply adhesive to the loading fixture, surface, or both Attach
the loading fixture to the coated surfaces Push downward; do not
twist Remove Teflon plug Remove excess adhesive
Slide 30
Attaching the Loading Fixtures Secure loading fixture until
adhesive cures Use magnetic or mechanical fixture holder or tape If
using tape, ensure it doesnt relax during adhesive cure
Slide 31
Scoring Around Loading Fixture Light scoring can be performed
to remove excess adhesive Scoring of the coating is not recommended
If scoring is performed, must be done carefully Scoring (if done)
must be reported with test results
Slide 32
Measuring Pull-off Adhesion Using the Type II Tester Model
No.Range 106/10-500 psi 106/2 (shown)0-1000 psi 106/30-2000 psi
(uses wrench) 106/40-3200 psi (uses wrench) 106/4AUse w/ 2 diameter
pull stubs (uses wrench) 106/50-30 psi
Slide 33
Measuring Pull-off Adhesion Using the Type II (fixed alignment)
Tester 1. Lower the jaw by turning the hand wheel (nut)
counterclockwise 2. Slide the jaw opening over the head of the
loading fixture 3. Verify levelness 4. Set the drag pin to zero
(push downward) 1 43 2
Slide 34
Measuring Pull-off Adhesion Using the Type II (fixed alignment)
Tester 5. Rotate hand wheel (nut) clockwise to increase load (
Slide 35
Measuring Pull-off Adhesion using the Type III (hydraulic)
Tester Insert pin through center hole of stainless steel loading
fixture (may need to loosen black threaded hand lever) Pull upwards
on the quick connect and allow the locking ring to engage the
outside flange of the loading fixture. Pull upwards to verify
locking ring is engaged
Slide 36
Measuring Pull-off Adhesion using the Type III (hydraulic)
Tester Return red sweep needle to zero (or zero set the digital
display) Rotate the black threaded handle clockwise until break
occurs or maximum pressure is achieved Read pressure from analog or
digital display Loading fixtures (stainless steel) can be cleaned
with heat clamp
Slide 37
Measuring Pull-off Adhesion using the Type IV (pneumatic)
Tester Device uses air pressure inside a piston to provide a
constant, perpendicular pull on a threaded loading fixture Piston
pressure is converted to psi (or Kpa) using conversion charts based
on piston size
Slide 38
Measuring Pull-off Adhesion using the Type IV (pneumatic)
Tester PistonRange F-10-500 psi F-20-1,000 psi F-40-2,000 psi
F-80-4,000 psi F-160-8,000 psi F-8/120-4,000/0-10,000 psi Round
base with pigtail hose Silicone rubber gasket (lifted upward) Round
threaded top plate
Slide 39
Measuring Pull-off Adhesion using the Type IV (pneumatic)
Tester Connect piston hose to the main air hose (brass coupling)
Push air hose connection into the base unit Insert CO2 cartridge
into sleeve Thread the CO2 sleeve onto the base unit
Slide 40
Measuring Pull-off Adhesion using the Type IV (pneumatic)
Tester Place piston over the loading fixture Thread top plate onto
the fixture until contact is made with the piston, then reverse the
top plate -1/2 turn to allow silicone gasket to raise Close the
Rate Valve (dont over-tighten) Rate Valve
Slide 41
Measuring Pull-off Adhesion using the Type IV (pneumatic)
Tester Turn the Power switch to the on position Push the peak reset
button Push in and hold the Run button, while slowly opening the
Rate Valve until pressure increases at ~2 psi/second Do not exceed
6 psi/ second On/off Peak Reset Run Rate valve
Slide 42
Measuring Pull-off Adhesion using the Type IV (pneumatic)
Tester Read the Piston Pressure from the digital display Convert
the Piston Pressure to psi (or Kpa) using the conversion chart
corresponding to the piston used and diameter of the loading
fixture Example: 46 psi piston pressure = 937.3 psi adhesion
strength (F4 piston and 0.5 diameter loading fixture)
Slide 43
Measuring Pull-off Adhesion using the Type V (hydraulic) Tester
Type V uses hydraulic pressure to apply perpendicular force to the
loading fixture Pull-off strength is read directly from digital
display Manual version is shown
Slide 44
Measuring Pull-off Adhesion using the Type V (hydraulic) Tester
Open the pressure relief valve and push actuator handle into
assembly Power-up tester (green) Verify LCD reads zero Select
pull-stub size (*) Select units (**) ***
Slide 45
Measuring Pull-off Adhesion using the Type V (hydraulic) Tester
Position actuator over loading fixture. Attach quick connect
coupling to head of fixture Close the pressure relief valve Pump
lever until digital display indicates pressure is applied
Slide 46
Measuring Pull-off Adhesion using the Type V (hydraulic) Tester
Continue pumping uniformly (
Slide 47
Measuring Pull-off Adhesion using the Type V (hydraulic) Tester
Automatic version applies hydraulic pressure to actuator without
pumping of a lever
Slide 48
Measuring Pull-off Adhesion using the Type VI (hydraulic)
Tester Type VI tester uses hydraulic pressure to apply
perpendicular force to the loading fixture Pull-off strength is
read directly from the gage dial (up to ~ 2,470 psi)
Slide 49
Measuring Pull-off Adhesion using the Type VI (hydraulic)
Tester Type VI tester consists of a turning crank/pressure gage
& testing head Verify crank and tightening wheel are in start
position Press 4 pistons against even surface to return oil to the
pump
Slide 50
Measuring Pull-off Adhesion using the Type VI (hydraulic)
Tester Lift outer ring of the quick release coupling; mount the
testing head to the loading fixture Release the quick connect and
listen for click, indicating it is locked into the groove Return
the red sweep needle to zero
Slide 51
Measuring Pull-off Adhesion using the Type VI (hydraulic)
Tester Turn the tightening wheel at base of pump until piston legs
contact surface and gage dial initiates movement Turn hand crank
smoothly & evenly until a break occurs or the maximum pressure
is reached Read pressure from gage dial (psi x 100 on red
dial)
Slide 52
Special Requirements for Pull-off Adhesion of Coatings on
Concrete Standard Test Method ASTM D7234-05 SSPC SP13/NACE No. 6,
Appendix A1.6 describes procedures for testing concrete coating
adhesion Testing procedures are similar; minor differences in
equipment and test procedures This section is not comprehensive
SSPC CCI (Concrete Coating Inspector) Training Program contains
more detail Four considerations described
Slide 53
Special Requirements for Pull-off Adhesion of Coatings on
Concrete 1. Scoring the coating Thick film coatings (>20 mils)
have lateral bond strength May produce misleading pull-off values
(false, high) Scoring through coating (down to the concrete
surface) is typically performed Scoring is done prior to attachment
of loading fixture (except if loading fixture is square) Scoring
coatings
Recording the Type and Location of Break Disregard any test
where glue break represents more than 50% If glue break occurs and
the pull-off value is greater than the acceptance value,
re-attachment is not necessary (report pass with pull-off strength
> X psi)
Slide 59
Pitfalls to Avoid Determine which tester to use. Different
testers generate different pull-off values on the same coating
Verify testing equipment has current calibration Perform testing in
triplicate The rigidity of the substrate can affect the testing
Clean the surface and the loading fixtures to reduce the
possibility of glue failures. Use care when abrading the surface to
prevent introduction of surface flaws Verify adhesive is compatible
with the coating Allow the adhesive to cure. Conducting pull tests
before adhesive is cured often results in glue breaks Verify
perpendicular pull Support pull-off device on vertical
surfaces
Slide 60
Reporting General Nature of Test Substrate type and coating
system (thickness, type, surface orientation) Field or laboratory
testing Air temperature and relative humidity Testing apparatus
employed; loading fixture type/dimensions Adhesive type employed
No. of tests performed Load applied (pull-off values, in psi, KPa
or MPa) Mean and range of pull-off values Location of break
(between coats, within a coat, between substrate surface and
primer, etc.) Note scoring, if employed (and any other deviations
from procedure)