Adhesion removal testing determines the adhesion of a coating to a substrate by applying pressure to a loading device glued to the coating. The tear test measures tensile strength, while the pull test uses an adhesion tester to exert force until the weakest component loses its bond. Results are recorded as tensile strength, adhesive rupture point, or cohesive failure point.
Adhesion removal testing, also called paint stripping testing, is a process used to determine the performance and adhesion of a coating to a particular substrate, such as concrete. This test is done by gluing a loading device, known as a dolly or stub, to the coating with an epoxy resin. A coherent measured pressure is then applied to this loader in an attempt to break the bond of the loader to the surface coating, break the bond of the coating to the substrate, or break the surface of the substrate itself.
As a near-surface test, the tear test determines the tensile strength of the bond, rather than the sheer strength of the coating, which is tested by additional procedures such as the knife test, scratch test, and tape test. The tear test should require a significant amount of pressure to be able to break the bond of suitable substrate coatings. In the case of stronger coatings, it is actually possible to break the substrate before the bond with the coating is broken.
The pull test is done using a machine called an adhesion tester. Pull testers come in three styles: mechanical, pneumatic, and hydraulic. This test rig is designed to provide the vertical pulling force needed to perform an accurate test. For the most accurate result, the pullout test equipment must deliver this force in a plane perpendicular to the test surface.
The adhesion tester works by exerting a controlled and measured force on the carriage. These loading devices are available in different sizes to accommodate the physical properties of various substrate types and to provide the ability to accurately determine a wider range of pull force measurements. The pull-off test ends when the weakest component in the system loses its bond with the other components. This system includes: the carriage, the epoxy adhesive, the surface coating and the substrate.
If the carriage is pulled out of the surface coating without damaging the adhesion of the coating to the substrate, the pressure measurement required to do so is recorded as the tensile strength of the surface coating. When the bond between the coating and the substrate is broken, this measurement is recorded as the adhesive rupture point. If the surface coating or substrate fails, this measurement is recorded as the cohesive failure point.
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