Overview
ISO 4628-6:2023 defines a standardized tape method to assess the degree of chalking of paint coatings. The document supplies pictorial reference standards and a clear procedure for removing chalking with adhesive tape, comparing residues against contrasting backgrounds, and reporting results. The standard emphasizes differentiating true degradation (loose powder) from adhering dirt and recommends using printed pictorial standards for reliable visual comparison.
Key Topics
- Principle: Chalk is lifted from the surface with a transparent adhesive tape and assessed against a contrasting background (black or white) to determine the chalking rating.
- Materials: Use a transparent, colourless self-adhesive tape of at least 15 mm width and a matt black or white background with short pile (card or velvet is suggested). The tape type affects results and shall be agreed and recorded.
- Procedure highlights:
- Allow the surface to dry at room temperature before testing.
- Apply firm pressure to a tape length of at least 40 mm, then remove perpendicularly and lay adhesive side down on the selected background.
- Assess immediately under consistent illumination and compare to the pictorial reference standards.
- For quantitative checks, a photoelectric transmittance method may be used: a transmittance below 70% of unused tape indicates chalking (only if residue pattern is homogeneous).
- Practical cautions: Distinguish dirt from true chalking (especially with slight chalking); natural weathering can deposit atmospheric dirt and skew results; perform blank tests for low-gloss coatings.
Applications
This part of ISO 4628 is intended for:
- Visual and instrumental evaluation of chalking on painted surfaces during quality control, weathering tests, and inspection.
- Producing consistent, traceable ratings for coatings research, product development, maintenance decisions, and comparative studies.
Benefits include a replicable visual scale, defined materials and steps to reduce inter-laboratory variability, and an option for instrumental quantification where appropriate.
Related Standards
- ISO 4628-1 - general introduction and designation system for defect and change ratings (numerical values correspond to ISO 4628-1).
- ISO 4618:2023 - provides the definition of "chalking" used in this document.
Reporting and Traceability
The standard requires test reports to include sample identification, reference to ISO 4628-6:2023, method details (weathering type, tape identification, background, illumination), numeric rating, whether the assessment was visual or instrumental, deviations, anomalies, and the test date. Recording the tape manufacturer and exact background used is essential for reproducibility.
For reliable visual assessment, the standard recommends using printed pictorial reference standards purchased from ISO member bodies rather than electronic copies.