An update on the revised international cross-cut paint testing standard
Published: September 2020
We’ve revised the international standard on how paint coatings resist separation when cut. This blog post reviews how the test has changed.
Paints and varnishes change the aesthetic appeal of objects, and also protect them. It’s therefore important they don’t delaminate; but how can you assess the resistance to separation of coatings in a consistent and reproducible way? By using BS EN ISO 2409:2020 Paints and varnishes. Cross-cut test.
This international standard has been around since 1972. It’s well-established and widely used wherever laboratory or field testing of paints and varnishes is conducted. Settings where it’s applied include in aerospace, rail and defence companies; in high precision engineering; by door and window suppliers; by paint and coating manufacturers; by aluminium products suppliers and metal façade experts; by architectural powder coating manufacturers; in test laboratories and by metal finishing producers.
Resistance to separation
2020 sees the publication of the fifth edition of the standard, which will replace the 2013 version. The document specifies a test method for assessing the resistance of paint coatings to separation from substrates when a right-angle lattice pattern is cut into the coating, penetrating through to the substrate.
The standard includes specifications on the apparatus used, in particular the cutting tool. It deals with general requirements as well as those for single and multi-blade cutting tools.
The standard then looks at how sampling should be approached; covers the preparation of test specimens, and then looks at the procedure to be followed.
Subsequent sections deal with the evaluation and expression of results; how to designate test results, the precision of results and test reports. The Annex covers examples of suitable procedures for removing loose paint which comprise brushing, using pressure-sensitive adhesive tape or the use of compressed air or nitrogen.
Pass/fail or classification
The method described in BS EN ISO 2409 may be used either as a quick pass/fail test or, where appropriate, as a six-step classification test. When applied to a multi-coat system, it’s possible to assess the resistance to separation of individual layers of the coating from each other.
Although the test is mainly intended for use in the laboratory, it’s also suitable for field testing. The test can be carried out on finished objects and/or on specially prepared test specimens.
Although the method can be applied to paint on hard (e.g. metal) and soft (e.g. wood and plaster) substrates, these different substrates need a different test procedure.
Note that this method is not suitable for coatings of thicknesses greater than 250 gm or for textured coatings. That’s because coatings designed to give a rough patterned surface will give results which show too much variation.
Revisions to the standard
Germany initially requested that BS EN ISO 2409 be updated when the standard was undergoing its systematic review. Members of the responsible ISO technical committee then agreed to proceed with a full revision.
As a result a number of changes have been made, the most important of which are that Clause 3 on "Terms and definitions" has been added; Clause 4 on "Principle" has been added; the general requirements for the use of single-cutting tools and multi-cutting tools have been updated; references to commercially available cutters have been deleted; coating of the test panels has been deleted from Clause 7, because final test specimen are assumed; and finally the text has been editorially revised and the normative references have been updated. It’s hoped these revisions will ensure the standard’s usefulness for many more years to come.