The standard test method covered in ASTM D4541-17 – Standard Test Method for Pull-Off Strength of Coatings Using Portable Adhesion Testers is used for evaluating the pull-off strength (otherwise known as adhesion) of a coating system from metal substrates. The Pull-off strength determined by this procedure is a performance property, and it may be referenced in specifications.
The pull-off test is performed by securing a loading fixture, such as a dolly or stud, to the surface of the coating being tested with a glue. A testing apparatus is attached to the loading fixture and aligned to apply tension to the test surface. The force applied to the loading fixture is then gradually increased and monitored until either the loading fixture is detached or a specified load value is reached.
While that is the general idea of the test, in accordance with the ASTM D4541-17 standard, pull-off strength testing of coatings can be carried out through five particular methods:
- Test Method B — Fixed Alignment Adhesion Tester Type II
- Test Method C — Self-Alignment Adhesion Tester Type III
- Test Method D — Self-Alignment Adhesion Tester Type IV
- Test Method E — Self-Alignment Adhesion Tester Type V
- Test Method F — Self-Alignment Adhesion Tester Type VI
Each of these testing methods varies in the apparatus used and ranges covered, as well as the procedures with which correlate. These methods are detailed in Annex A of the ASTM D4541-17 document.
Please note that previous versions of ASTM D4541 included a Test Method A. However, this has been eliminated, as its main use is for testing concrete substrates. For guidance on the standard test method for testing the adhesion of coatings on concrete, refer to ASTM D7234-19: Standard Test Method for Pull-Off Adhesion Strength of Coatings on Concrete Using Portable Pull-Off Adhesion Testers.
There are two main protocols for this standard test. Protocol 1 (test to fracture) determines the maximum perpendicular forces that a surface area can withstand before a plug of material is detached. Protocol 2 (pass/fail) determines if the coated surface remains intact at a defined load criteria.
The protocol determines the goal of the test. Therefore, the purchaser or specifier is to designate a specific test method procedure and test protocol when calling out this standard.
Detailed guidance on the test preparation, apparatus, test procedure, calculation, and reporting of results can be found in the ASTM D4541-17 document.
ASTM D4541-17 – Standard Test Method for Pull-Off Strength of Coatings Using Portable Adhesion Testers is available on the ANSI Webstore.