This test method covers a procedure for evaluating the
pull-off strength (commonly referred to as adhesion) of a
coating system from metal substrates. Pull-off strength of
coatings from concrete is described in Test Method D7234. The
test determines either the greatest perpendicular force (in
tension) that a surface area can bear before a plug of material
is detached, or whether the surface remains intact at a pre�scribed force (pass/fail). Failure will occur along the weakest
plane within the system comprised of the test fixture, adhesive,
coating system, and substrate, and will be exposed by the
fracture surface. This test method maximizes tensile stress as
compared to the shear stress applied by other methods, such as
scratch or knife adhesion, and results may not be comparable.
Significance and Use
The pull-off strength of a coating is an important
performance property that has been used in specifications. This
test method serves as a means for uniformly preparing and
testing coated surfaces, and evaluating and reporting the
results. This test method is applicable to any portable apparatus
meeting the basic requirements for determining the pull-off
strength of a coating.
Variations in results obtained using different devices or
different substrates with the same coating are possible (see
Section 10). Therefore, it is recommended that the type of
apparatus and the substrate be mutually agreed upon between
the interested parties.
The purchaser or specifier shall designate a specific test
method, that is, B, C, D, E, or F when calling out this standard.
Apparatus :-
- Adhesion Tester, commercially available, or comparable
apparatus - Loading Fixtures, having a flat surface on one end that
can be adhered to the coating and a means of attachment to the
tester on the other end. - Detaching Assembly (adhesion tester), having a cen�tral grip for engaging the fixture.
- Base, on the detaching assembly, or an annular bearing
ring if needed for uniformly pressing against the coating
surface around the fixture either directly, or by way of an
intermediate bearing ring. A means of aligning the base is
needed so that the resultant force is normal to the surface.