Overview
EN ISO 4624:2023 - Paints and varnishes: Pull-off test for adhesion (ISO 4624:2023) is the CEN-endorsed international method for assessing adhesion of single or multi-coat paint and varnish systems by a controlled tensile (pull-off) test. The standard specifies three distinct test methods (A, B and C) using bonded dollies and a tensile tester to measure the force required to detach or rupture a coating perpendicular to the substrate. EN ISO 4624:2023 supersedes EN ISO 4624:2016 and includes technical updates such as added guidance for larger dollies (up to 100 mm) for concrete and new requirements on adhesive selection relative to substrate/coating materials.
Key Topics and Requirements
- Three methods prescribed
- Method A: Two-dolly (sandwich) configuration - suitable for rigid and deformable substrates (thin metal, plastics, wood).
- Method B: Single-dolly testing from one side - suitable for rigid substrates only.
- Method C: Use of dollies where one dolly acts as the painted substrate (special configurations).
- Substrate considerations: Different procedures are given for deformable vs rigid substrates; sandwich constructions are recommended to avoid substrate distortion.
- Adhesives and dollies: Dollies are bonded to cured coatings using suitable adhesives; the standard includes requirements for adhesive selection and dolly sizes (including larger sizes for concrete).
- Measurements and results: The test records breaking strength (tensile stress at failure) and the nature of the fracture (adhesive/cohesive failure), providing relative adhesion ratings.
- Preparation and conditioning: Specifies sample preparation, coating application, drying/curing, thickness control and ambient conditioning in line with referenced ISO documents.
- Precision and reporting: Includes guidance on number of determinations, ambient conditions, and the required content of test reports.
Applications and Users
- Practical uses
- Quality control for paint and coating production
- Comparative R&D testing of coating formulations and surface treatments
- Service-life qualification and specification compliance
- Failure analysis and root-cause investigation of coating breakdown
- Who uses it
- Coatings manufacturers and formulators
- Independent test laboratories and QC departments
- Specifiers, architects and contractors for protective coatings (metal, concrete, wood, plastics)
- Research institutions studying adhesion performance
Related Standards
- ISO 1513 - Examination and preparation of test samples
- ISO 1514 - Standard panels for testing
- ISO 2808 - Determination of film thickness
- ISO 3270 - Temperatures and humidities for conditioning and testing
- ISO 4618 - Paints and varnishes vocabulary
- ISO 15528 - Sampling
- ISO 2409 - Cross-cut test (alternative adhesion evaluation)
EN ISO 4624:2023 is essential for anyone specifying or testing coating adhesion, offering standardized, reproducible pull-off test methods for a wide range of substrates and industrial applications.