Overview
EN ISO 4628-1:2016 (CEN endorsed) provides the general introduction and designation system used throughout ISO 4628 for the evaluation of degradation of coatings. The standard defines a uniform convention to describe the quantity, size and intensity of coating defects and uniform appearance changes using a numerical rating scale from 0 to 5. Part 1 establishes the principles applied across the series and is intended primarily for defects caused by ageing and weathering, including uniform changes such as yellowing.
Key Topics
- Rating scale (0–5): A numerical system where 0 denotes no detectable defect or change and 5 denotes very severe change; intermediate whole-number ratings (and permitted half-steps if specified) provide discrimination across the full range.
- Quantity of defects: Designation follows a qualitative scale (e.g., 0 = none, 1 = very few, up to 5 = dense pattern). A grid method (see ISO 10289) may be used for scattered small defects.
- Size of defects: Average size is designated using the Sn notation (S = size, n = rating). Typical visibility thresholds are defined (e.g., S2 just visible with normal corrected vision; S4 > 0.5 mm up to 5 mm).
- Intensity of uniform changes: Colour or uniform appearance changes (such as yellowing) are rated 0–5 (0 = unchanged, 5 = very marked change).
- Assessment conditions: Visual assessment is carried out under suitable illumination as specified in ISO 13076, initially without magnification and then with magnification where required.
- Expression of results: Results combine defect type, quantity and size (for example, "blistering 2(S2)") and should include area or percentage coverage and any clarifying remarks (e.g., "confined to edges").
Applications
This part of ISO 4628 is a foundational tool for:
- Routine and laboratory inspection of painted and varnished surfaces to assess degradation after ageing, weathering or exposure tests.
- Quality control and acceptance criteria in manufacturing and maintenance of coatings.
- Reporting and comparison of inspection results where consistent, repeatable terminology and ratings are required.
- Assessing defect types not covered by other parts of ISO 4628 when a general designation system is needed.
Practical benefits include consistent inspection language, clearer test reports, and compatibility with pictorial or specific evaluation methods provided in subsequent parts of the ISO 4628 series.
Related Standards
ISO 4628 is a multipart standard. Relevant associated documents include:
- ISO 4628-2 - Assessment of degree of blistering
- ISO 4628-3 - Assessment of degree of rusting
- ISO 4628-4 - Assessment of degree of cracking
- ISO 4628-5 - Assessment of degree of flaking
- ISO 4628-6 & -7 - Assessment of degree of chalking (tape and velvet methods)
- ISO 4628-8 - Delamination and corrosion around artificial defects
- ISO 4628-10 - Filiform corrosion
Normative references and assessment support:
- ISO 13076 - Lighting and procedure for visual assessments of coatings (illumination requirements)
- ISO 10289 - Grid method for assessing scattered small defects
Test Reporting (minimum contents)
A compliant test report shall include identification of the coating, a reference to ISO 4628-1, surface examined and location, assessment results (type, rating and size), illumination used, anomalies observed and the examination date.
Using EN ISO 4628-1:2016 ensures standardized, comparable evaluation of coating degradation across laboratories, inspectors and regulatory contexts.
