DeFelsko Adhesion Testers

Adhesion is the ability for a coating such as paints and varnishes to adhere to a substrate termed as ‘substrate adhesion’ or the ability for a coating to adhere to multiple coats in the system which is termed ‘inter-coat adhesion’. For coatings to perform satisfactorily, they must adhere to the substrate on which they are applied including metal, concrete, wood, and more.

What is pull-off adhesion testing?

In accordance with ASTM D4541/D7234, ISO 4624, and others, adhesion testers evaluate the adhesion (pull-off strength) of a coating by determining the greatest tensile pull-off force that it can withstand before detaching. Breaking points, demonstrated by fractured surfaces, occur along the weakest plane within the system consisting of the dolly (loading fixture, pull stub), glue, coating layer(s), and the substrate.

The PosiTest AT series measures the force required to pull a specified test diameter of coating away from its substrate using hydraulic pressure.

Why is it necessary to test adhesion?

The goal of adhesion testing is to produce a coating failure. Coating adhesion is an indicator of how well the surface was prepared and how well the coating has bonded to the surface and/or additional coating layers. Testing adhesion offers a quantifiable method of determining if a paint or coating system is fit-for-purpose and ready to meet the quality demands of job specifications.