Cohesive and adhesive failure
The two ways a coating can break in an adhesion test. Cohesive failure runs through the film itself, meaning the bond to the substrate was the stronger of the two. Adhesive failure follows the interface with the substrate, which implicates preparation or contamination rather than the coating.
This distinction is the reason an adhesion test is worth running. A cohesive failure measures a property of the coating; an adhesive failure measures the job that was done underneath it.
A result that reads as acceptable on strength but fails adhesively at the steel is a warning, not a pass — it says the bond gave way first, and the same surface will do it again under service load.
Sources and references
- StandardASTM D4541-22 — Standard Test Method for Pull-Off Strength of Coatings Using Portable Adhesion TestersASTM International · accessed August 29, 2026