🔩 Assessment of the degree of cracking of paint coatings by comparison with pictorial standards — quantity of cracks on a 0–5 scale (from none to a dense pattern), size on a 0–5 scale (from not visible under ×10 magnification to a width above 1 mm), depth: a — surface cracks of the top coat, b — through the top coat, c — through the whole system, notation e.g. 2(S3)b, PN-EN ISO 4628-4

Materials and NDT PN-EN ISO 4628-4

Overview

WHAT THE STANDARD COVERS. Scope from the PKN catalogue card of PN-EN ISO 4628-4:2016-03 (English version), in full (our translation of the Polish card text): “This part of ISO 4628 specifies a method for assessing the degree of cracking of coatings by comparison with pictorial standards. NOTE See ISO 4628-1 for the system for designating the quantity and size of defects and the intensity of changes in appearance of coatings and for the general principles of the system.” We DO NOT HAVE the text of the 2016 edition: we read the final draft ISO/FDIS 4628-4:2015 (voting 17.09–17.11.2015) from the iTeh preview, from the cover to Figure A.2 of Annex A — Clauses 1–6, Figures 1–2 and the beginning of Annex A; the second preview (SIST EN ISO 4628-4:2016) contains only the earlier draft ISO/DIS 4628-4 of 2014. We therefore give the numbers from the FDIS — they may have been changed editorially in the published edition.

ACCORDING TO THE TEXT OF ISO/FDIS 4628-4:2015 (Clauses 1–6, Figures 1–2, Annex A up to Figure A.2). The standard was prepared by ISO/TC 35, subcommittee SC 9 (secretariat BSI). The third edition replaces the second (ISO 4628-4:2003); according to the foreword of the DIS the changes are the introduction in Table 2 of a lower limit for visual assessment of defects and the reference to ISO 13076 for illumination. Scope (Clause 1): a method for assessing the degree of cracking of coatings by comparison with pictorial standards; the designation system is described in ISO 4628-1. Normative references: ISO 4628-1 and ISO 13076. Definition (3.1): degree of cracking — rating characterizing cracks in a coating in terms of quantity, size and depth. Assessment (Clause 4): the quantity of cracking is assessed according to Table 1, using as an example Figure 1 (cracking without preferential direction) or Figure 2 (cracking in one preferential direction, which occurs with substrates such as wood, “anisotropic” substrates); other forms of cracking occur, but the principle of assessing quantity is the same. Table 1 — quantity of cracks: 0 — none, i.e. no detectable cracks; 1 — very few, i.e. small, barely significant number of cracks; 2 — few, i.e. small but significant number; 3 — moderate number; 4 — considerable number; 5 — dense pattern of cracks. If specified, the average size of the cracks is assessed according to Table 2: 0 — not visible under ×10 magnification; 1 — only visible under magnification up to ×10; 2 — just visible with normal corrected vision (up to 0,2 mm); 3 — clearly visible with normal corrected vision (larger than 0,2 mm up to 0,5 mm); 4 — large cracks, larger than 0,5 mm up to 1 mm wide; 5 — very large cracks, generally more than 1 mm wide; footnote: defects larger than 0,2 mm are typically visible with normal corrected vision. With cracks of various sizes the rating of the largest cracks numerous enough to be typical of the area is quoted. If possible, the depth of cracking is indicated by reference to the level of the coating system to which the cracks penetrate; three main types are distinguished: a) surface cracks which do not fully penetrate the top coat (“checking”); b) cracks which penetrate the top coat, the underlying coat(s) being substantially unaffected; c) cracks which penetrate the whole coating system. The assessment is carried out under good illumination according to ISO 13076. Expression of results (Clause 5): numerical ratings of quantity and — if specified — size, together with the depth (a, b or c) and the approximate dimensions of the area or its proportion of the total area in percent; example: quantity 2, size 3, cracks through the top coat with the underlying coats unaffected — “cracking; degree of cracking 2(S3)b”; the assessment may be amplified in words, e.g. “cracking in one preferential direction”, using the descriptions in Annex A. Test report (Clause 6): data identifying the coating, a reference to ISO 4628-4, type, size and location of the surface examined, result according to Clause 5, illumination, unusual features, date of examination. Figures 1 and 2: panels of area 100 cm² to 200 cm² for quantities 1–5; Figure 2 — cracking in one direction, e.g. due to brush marks or wood grain. Annex A (informative): examples of types of cracking with ASTM (e.g. ASTM 8, 6, 4, 2) and TNO designations — Figure A.1 “irregular”, Figure A.2 “long line”; this is where the extract we read ends.

STATUS (cards as of 02.10.2026). The card of PN-EN ISO 4628-4:2016-03 (English version) has no “Withdrawn” header — the standard is CURRENT: published 08-03-2016, 26 pages, price group M, Chemistry Sector, KT 175 Paints and Varnishes, ICS 87.040, “Introduces: EN ISO 4628-4:2016 [IDT], ISO 4628-4:2016 [IDT]”, “Replaces: PN-EN ISO 4628-4:2005 – Polish version”. PN-EN ISO 4628-4:2005 (Polish version, introduced ISO 4628-4:2003) — withdrawn 08-03-2016 and replaced by the 2016-03 edition. The PKN search for “PN-EN ISO 4628-4” (02.10.2026) also shows PN-EN ISO 4628-4:2004 (English) and PN-ISO 4628-4:1999. There is no Polish version of the 2016 edition. Referenced standards: PN-EN ISO 13076:2020-03 (lighting and procedure for visual assessment of coatings; introduces ISO 13076:2019) and PN-EN ISO 4628-1:2016-03 (designation system) — both without a “Withdrawn” header (cards, read 02.10.2026).

HOW MANY LABORATORIES AND IN WHAT FORM (copy of the accreditation scope database, data up to 17.09.2026, read 02.10.2026). The number 4628-4 appears in 9 records at 9 laboratories: AB 023, AB 089, AB 128, AB 163, AB 369, AB 1424, AB 1552, AB 1631, AB 1700. In the current scopes on the PCA website (read 02.10.2026) the number appears at all 9: with the year “2016-03” at AB 089, AB 163, AB 1424, AB 1552, AB 1631 and AB 1700, without a year at AB 023, AB 128 and AB 369. No row with the number is set in bold italics (at AB 1700 the suspension concerns another part of the scope). The “Laboratories” tab searches entries BEGINNING WITH “PN-EN ISO 4628-4” and shows all 9 laboratories and 9 positions — checked with the tab query on the labcoda.pl production server on 02.10.2026.

WHAT THE LABORATORIES TEST (positions in PCA). The same 9 laboratories as for Part 5 (flaking): paint coatings, paint systems on metal substrates, coating products; property “cracking” or “assessment of degree of cracking”, visual method, at AB 023 “also in situ”; at AB 1552 and AB 1424 next to PN-EN ISO 4628-1:2016-03, at AB 128 next to ASTM D714 (blistering) in the same group of assessments.

WHERE A SEEMINGLY CORRECT RESULT IS EASY TO GET. In quantity: the 0–5 scale is DESCRIPTIVE (from “very few” to “dense pattern”), not numerical — the comparison with Figure 1 or 2 decides; with a wooden substrate or brush marks Figure 2 has to be used. In size: the rating is required only when specified; rating 2 reaches up to 0,2 mm, and the 0,2 mm limit is the threshold of visibility with normal corrected vision — ratings 0 and 1 require a ×10 magnifier. In depth: type a (“checking”) does not penetrate the top coat; confusing a with b changes the conclusion about protection of the substrate at the same numbers. In the text: the numbers come from the FDIS draft, not from the published 2016 edition.

WHAT WE DO NOT GIVE. We do not have the published text of the 2016 edition or the rest of Annex A (figures after A.2 and descriptions of the other types of cracking); we do not describe the photographs of the standards or the lighting requirements of ISO 13076.

Method principle

The coating surface under test is compared visually with pictorial standards (Figure 1 or 2) and the quantity of cracks is rated on a descriptive 0–5 scale, and if specified the size on a 0–5 scale (from not visible under ×10 magnification through the thresholds of 0,2 mm, 0,5 mm and 1 mm width) and the depth (a — within the top coat, b — through the top coat, c — through the whole system) under lighting according to ISO 13076; the result is noted e.g. as 2(S3)b.

Applications

• Paint coatings and paint systems on metal substrates after ageing and corrosion tests — 9 laboratories, always together with other parts of ISO 4628
• In situ assessment of coatings on structures (AB 023)
• Coatings on wood and with marked brush marks — cracking in one direction according to Figure 2

Key parameters

Standard

Standard number

PN-EN ISO 4628-4:2016-03 (wersja angielska; EN ISO 4628-4:2016 IDT, ISO 4628-4:2016 IDT)

Title (PL)

Farby i lakiery — Ocena zniszczenia powłok — Określanie ilości i rozmiaru uszkodzeń oraz intensywności jednolitych zmian w wyglądzie — Część 4: Ocena stopnia spękania

Title (EN)

Paints and varnishes — Evaluation of degradation of coatings — Designation of quantity and size of defects, and of intensity of uniform changes in appearance — Part 4: Assessment of degree of cracking

Step-by-step procedure

1. Preparing the assessment

   Description of the surface examined (type, size, location); lighting according to ISO 13076. PN-EN ISO 4628-4:2016-03 current (cards as of 02.10.2026).

2. Quantity

   Comparison with Figure 1 (without preferential direction) or 2 (one direction — wood, brush marks) and rating 0–5 according to Table 1.

3. Size (if specified)

   Rating 0–5 according to Table 2 for the largest cracks typical of the area; ratings 0 and 1 — with a ×10 magnifier, from rating 2 — by eye.

4. Depth

   Where possible, indication of type a, b or c according to the level to which the cracks penetrate.

5. Result and report

   Notation e.g. “degree of cracking 2(S3)b”, dimensions or proportion of the area, verbal description according to Annex A, lighting, unusual features, date of examination.

Required equipment and apparatus

Health and safety (OHS)

• Visual assessment without reagents; for in situ assessment — rules for work on a structure; the draft standard we read contains no safety warnings
• TECHNICAL NOTE: the quantity scale is descriptive and requires comparison with the appropriate figure; the size numbers in this entry come from the draft ISO/FDIS 4628-4:2015, not from the published edition

Frequently asked questions