Bill CorbettKTA-Tator, Inc.

Coating Adhesion Testing Methods and EquipmentWebinar Content:

Why Measure Adhesion Properties?What is Being Measured?Selecting an Adhesion Testing MethodMeasuring Adhesion by the Tape TestMeasuring Adhesion by the Knife TestMeasuring 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 AdhesionReporting

Learning OutcomesCompletion 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

Learning Outcomes, continuedDescribe 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

Why Measure Adhesion Properties?Determine

specification complianceCommon in-process

inspection of TSCDetermine

maintenance strategy for existing coating systems

Adhesion data is not typically a predictor of coating performance

What is Being Measured?Measuring Coating Strength at Different

PlanesAdhesion 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 variableNo industry-wide adhesion acceptance valueMinimum adhesion values may be on a PDS or

in a specification

Selecting a Test Method

ASTM Standard

Method

D 3359-09 Adhesion By Tape Test

D 6677-07 Knife Adhesion

D 4541-09 Pull-off Strength of Coatings Using Portable Adhesion Testers

D 7234-05 Pull-off Strength of Coatings on Concrete Using Portable Pull-off Adhesion Testers

Selecting a Test MethodTape and Knife Adhesion require minimal

equipment and can be conducted quicklyEvaluate “shear” or “peel” strength (peel-back)

Pull-off adhesion requires specialized equipment and the testing takes comparatively longer to performEvaluates pull-off strength (resistance to

perpendicular pull)Cannot compare data, since testing mechanisms

are differentAdhesion testing is destructive to the coating film

Measuring Adhesion By Tape Test

EquipmentSteel ruler or guideUtility knifeBrushAdhesive tapeMagnifierASTM Test MethodCross-cut Tester

(alternative to knife and guide)

Measuring Adhesion By Tape TestStep 1: Select test area(s) and conduct triplicate

tests per areaStep 2: Determine the thickness of the coating

systemStep 3: Select the test method based on the

coating thicknessMethod A (X-cut): Coating thickness > 5 milsMethod 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)

Measuring Adhesion By Tape TestMethod 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”

Measuring Adhesion By Tape TestMethod A (X-cut)Remove cutting debrisRemove 2 laps of tape

(discard)Apply 3” piece of tape

to X-cutCover all of X-cutAssure good tape

contactRemove tape within

90 +/- 30 secondsRemove tape 180°

back across X-cut (do not pull upwards)

Measuring Adhesion By Tape TestMethod A (X-cut)

Rating Description

5A No peeling or removal

4A Trace peeling or removal along the incisions

3A Jagged removal along the incisions up to 1/16” on either side

2A Jagged removal along the incisions up to 1/8” on either side

1A Removal of most of the coating from the area of the “X” under the tape

0A Removal of coating beyond the area of the “X”

Measuring Adhesion By Tape TestMethod 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

Measuring Adhesion By Tape TestMethod B (Cross-cut)Remove cutting debrisRemove 2 laps of tape

(discard)Apply 3” piece of tape

to gridCover all of gridAssure good tape

contactRemove tape within

90 +/- 30 secondsRemove tape 180°

back across cross-cut (do not pull upwards)

Measuring Adhesion By Tape TestMethod B (Cross-cut)Ratin

g% Description

5B 0% Edges of cuts completely smooth

4B <5% Small flakes of coating detached at intersections

3B 6-15% Small flakes of coating detached along edges & at intersections

2B 16-35%

Coating flaked along edges and parts of squares

1B 36-65%

Coating flaked along edges in large ribbons and whole squares detached

0B >65% Flaking & detaching worse than 1B

Measuring Adhesion By Knife TestEquipment

Steel ruler or guideUtility knifeASTM Test Method

Measuring Adhesion By Knife TestSelect test areaMake 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

Measuring Adhesion By Knife Test

Rating

Description

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”

Pitfalls to AvoidASTM D3359 is for coatings on metallic surfacesDull knife blades can produce erroneous resultsMaintain proper spacing between incisions when

employing the cross-cut tape adhesion methodWhen 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 properlyTape may not be effective in cold temperatures

What Tape Should be Used?Note 5 in the current standard lists

Permacel 99 as suitablePermacel 99 discontinued in 2009No immediate replacementIntertape 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

ReportingSubstrate type and coating system; method of

cureEnvironmental conditions (temperature and RH)No. of tests performedManufacturer and type of tape employed (when

used)Mean and range of ratingsLocation of Break (between coats, within a coat,

between substrate surface and primer, etc.)

Measuring Pull-off AdhesionASTM 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

Preparing the Test SurfacesRemove 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

Loading Fixture Design

Fixed Alignment Type II

Self-AligningType III

Self-AligningType VI

Self-AligningType VSelf-Aligning

Type IV

Preparing the Loading FixturesLoading 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

Selecting an AdhesiveHigh solids epoxy

adhesivesCyanoacrylate

adhesiveEnsure compatibility

with coatingUV curable adhesive

available with Type IV tester (requires special loading fixtures with transparent base)

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

Attaching the Loading Fixtures(Type III Tester)Insert Teflon® plugApply adhesive to the

loading fixture, surface, or both

Attach the loading fixture to the coated surfaces

Push downward; do not twist

Remove Teflon® plugRemove excess adhesive

Attaching the Loading FixturesSecure loading

fixture until adhesive cures

Use magnetic or mechanical fixture holder or tape

If using tape, ensure it doesn’t “relax” during adhesive cure

Scoring Around Loading FixtureLight 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

Measuring Pull-off Adhesion Using the Type II Tester

Model No. Range

106/1 0-500 psi

106/2 (shown)

0-1000 psi

106/3 0-2000 psi (uses wrench)

106/4 0-3200 psi (uses wrench)

106/4A Use w/ 2” diameter pull stubs(uses wrench)

106/5 0-30 psi

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 levelness4. Set the drag pin to

zero (push downward)

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2

Measuring Pull-off Adhesion Using the Type II (fixed alignment) Tester5. Rotate hand wheel

(nut) clockwise to increase load (<150 psi/second)

6. Break (or maximum force) should occur in 100 seconds or less

7. Record the value corresponding to the bottom of the drag pin, E.g. 6 is 600 psi

Measuring Pull-off Adhesion using the Type III (hydraulic) TesterInsert 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

Measuring Pull-off Adhesion using the Type III (hydraulic) TesterReturn 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

Measuring Pull-off Adhesion using the Type IV (pneumatic) TesterDevice 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

Measuring Pull-off Adhesion using the Type IV (pneumatic) Tester

Piston Range

F-1 0-500 psi

F-2 0-1,000 psi

F-4 0-2,000 psi

F-8 0-4,000 psi

F-16 0-8,000 psi

F-8/12 0-4,000/0-10,000 psi

• Round base with pigtail hose• Silicone rubber gasket (lifted upward)• Round threaded top plate

Measuring Pull-off Adhesion using the Type IV (pneumatic) TesterConnect 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

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 ¼-1/2 turn to allow silicone gasket to raise

Close the Rate Valve (don’t over-tighten)

Rate Valve

Measuring Pull-off Adhesion using the Type IV (pneumatic) TesterTurn the Power switch

to the “on” positionPush 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 PeakReset

Run

Rate valve

Measuring Pull-off Adhesion using the Type IV (pneumatic) TesterRead the Piston Pressure

from the digital displayConvert 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)

Measuring Pull-off Adhesion using the Type V (hydraulic) TesterType V uses

hydraulic pressure to apply perpendicular force to the loading fixture

Pull-off strength is read directly from digital display

Manual version isshown

Measuring Pull-off Adhesion using the Type V (hydraulic) TesterOpen the pressure

relief valve and push actuator handle into assembly

Power-up tester (green)

Verify LCD reads zero

Select pull-stub size (*)

Select units (**)* **

Measuring Pull-off Adhesion using the Type V (hydraulic) TesterPosition 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

Measuring Pull-off Adhesion using the Type V (hydraulic) TesterContinue pumping

uniformly (<150 psi/ second)

Monitor pull rate using LCD display (psi/s)

Display holds maximum pressure of pull-off

Record value, or press memory pad (*) to store value

Depress green button to zero display *

Measuring Pull-off Adhesion using the Type V (hydraulic) TesterAutomatic version

applies hydraulic pressure to actuator without pumping of a lever

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)

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

Measuring Pull-off Adhesion using the Type VI (hydraulic) TesterLift 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

Measuring Pull-off Adhesion using the Type VI (hydraulic) TesterTurn 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)

Special Requirements for Pull-off Adhesion of Coatings on ConcreteStandard 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 comprehensiveSSPC CCI (Concrete Coating Inspector)

Training Program contains more detailFour considerations described

Special Requirements for Pull-off Adhesion of Coatings on Concrete1. 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 performedScoring is done prior to attachment of loading

fixture (except if loading fixture is square)Scoring coatings <20 mils may also be requiredWhen attaching loading fixture, verify adhesive

does not flow into groove

Special Requirements for Pull-off Adhesion of Coatings on Concrete2. Loading Fixture Size

Unlike steel, concrete is non-uniform and contains cement and aggregate

Round loading fixture diameter should be 2” (50 mm) to ensure test is performed over a representative area

Square loading fixtures are used with some testers

3. Loading Rate The pressure loading rate should be 30 psi/second;

the test should be completed in 5-30 seconds

Special Requirements for Pull-off Adhesion of Coatings on Concrete4. Compressive Vs. Tensile Strength

Concrete has high compressive strength (i.e., 4000 psi), but low tensile strength (i.e., 400 psi)

Low pull-off values common Plane of fracture commonly within the

concrete When fracture occurs in the concrete, report

the minimum coating tensile adhesion properties; actual coating tensile strength remains unknown

Recording the Type and Location of BreakAdhesion Break: A break between coating layers

or between the substrate and first coating layerCohesion Break: A break within a single coating

layerGlue Break: Coating adhesion and/or cohesion

strength exceeds bonding strength of the adhesive

If multiple locations of break occur, estimate the percentage of each (e.g., 75% cohesion within primer; 25% adhesion between primer and intermediate coats)

Illustration of Various Illustration of Various Locations of BreakLocations of Break

Recording the Type and Location of BreakDisregard 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”)

Pitfalls to AvoidDetermine which tester to use. Different testers

generate different pull-off values on the same coatingVerify testing equipment has current calibrationPerform testing in triplicateThe rigidity of the substrate can affect the testingClean 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 coatingAllow the adhesive to cure. Conducting pull tests before

adhesive is cured often results in glue breaksVerify perpendicular pullSupport pull-off device on vertical surfaces

ReportingGeneral Nature of Test

Substrate type and coating system (thickness, type, surface orientation)

Field or laboratory testingAir temperature and relative humidityTesting apparatus employed; loading fixture type/dimensionsAdhesive type employedNo. of tests performedLoad applied (pull-off values, in psi, KPa or MPa)Mean and range of pull-off valuesLocation of break (between coats, within a coat, between

substrate surface and primer, etc.)Note scoring, if employed (and any other deviations from

procedure)

THE ENDTHE END