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(Inspection) Adhesion Testing: How to Make It Stick in Assuring Coating Performance

It has become common practice for specification writers to require minimum tensile pull-off adhesion strength values as part of the acceptance criteria for protective coating work for concrete substrates.  These values are convenient for specifiers because a minimum number provides a black and white basis upon which to define success versus failure. But there is much more to performing and evaluating adhesion testing than a hard and fast number.

Product Number: 63-COAT_DEC21
Author: Randy Nixon / Kirk Shields,
Publication Date: 2021
Industry: Coatings
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It has become common practice for specification writers to require minimum tensile pull-off adhesion strength values as part of the acceptance criteria for protective coating work for concrete substrates.  These values are convenient for specifiers because a minimum number provides a black and white basis upon which to define success versus failure. But there is much more to performing and evaluating adhesion testing than a hard and fast number.  The minimum pull-off value is widely specified without any consideration for substrate strength, surface profile, substrate conditions, the test positions, coating type, or coating thickness (project specific conditions).  What also gets missed with this practice are several essential quality considerations including:

 

  1.                   It’s a destructive test. 
  2.                   The failure plane or interface for the load fixture is generally of greater import than the pull-off strength value itself.
  3.                   The appropriate test standard is often not followed.
  4.                   What equipment was used in establishing an acceptance value? 
  5.                   Not knowing when to perform the tests, how to perform the tests, and how to interpret the results. 
  6.                   How frequent the tests will be performed, by whom, and what the overall acceptance criteria really should be. 

 

This paper will provide guidance on how to avoid these commonplace pitfalls. Using adhesion testing, not as a pass or fail Q.C. criteria in specifications, but rather as a properly executed Q.A. tool.

It has become common practice for specification writers to require minimum tensile pull-off adhesion strength values as part of the acceptance criteria for protective coating work for concrete substrates.  These values are convenient for specifiers because a minimum number provides a black and white basis upon which to define success versus failure. But there is much more to performing and evaluating adhesion testing than a hard and fast number.  The minimum pull-off value is widely specified without any consideration for substrate strength, surface profile, substrate conditions, the test positions, coating type, or coating thickness (project specific conditions).  What also gets missed with this practice are several essential quality considerations including:

 

  1.                   It’s a destructive test. 
  2.                   The failure plane or interface for the load fixture is generally of greater import than the pull-off strength value itself.
  3.                   The appropriate test standard is often not followed.
  4.                   What equipment was used in establishing an acceptance value? 
  5.                   Not knowing when to perform the tests, how to perform the tests, and how to interpret the results. 
  6.                   How frequent the tests will be performed, by whom, and what the overall acceptance criteria really should be. 

 

This paper will provide guidance on how to avoid these commonplace pitfalls. Using adhesion testing, not as a pass or fail Q.C. criteria in specifications, but rather as a properly executed Q.A. tool.

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