8.1 EXAMINING THE DOLLY
a)
Cohesive Failure:
The coating fails within the body of a
coating layer leaving the same coating on the surface and on
the dolly face.
b)
Adhesive failure:
Is a failure at the interface between layers
(intercoat) where one pulls away from the other. The
“coating” on the dolly face will not be the same as that on the
test area.
c)
Glue failure:
When no coating is present on the dolly it must be
recorded as a failure of the glue. This is normally due to
incorrect or insufficient mixing of the component parts of the
adhesive, incompatibility between the adhesive, the coating,
the dolly, and / or the test surface - see Section 5 - ‘Securing
the Dolly’ on page 8 for more information.
8 ASSESSING THE RESULTS
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Dolly Face
Substrate
a) 100% Cohesive Failure
b) 100% Adhesive Failure Between Two
Layers
c) Glue Failure
Layer 2
Substrate
Glue
Dolly Face
Key
Layer 1
Layer 3
Many National and International Standards including ISO 4624 & ASTM D4541, require the user to
record not only the pull-off force but also the nature of the fracture by examining the bottom of the dolly
and assessing the adhesive / cohesive failure.
