🔩 Degree of blistering of paint and other coatings — comparison with pictorial standards of blisters of sizes 2–5 and quantities (densities) 2–5, assessment in good lighting according to ISO 13076, designation in the form e.g. "2(S2)" together with the size of the area evaluated, PN-EN ISO 4628-2

Materials and NDT PN-EN ISO 4628-2

Overview

WHAT THE STANDARD COVERS. Scope from the PKN card, in full (our translation): "This part of ISO 4628 specifies a method for assessing the degree of blistering of coatings by comparison with pictorial standards. The pictorial standards in this part of ISO 4628 illustrate blisters of sizes 2, 3, 4 and 5, and their quantities (densities) 2, 3, 4 and 5 for each size. 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 have a sample of ISO 4628-2:2016 (third edition of 2016-01-15) from the cover to Figure 3 (page 5).

ACCORDING TO THE 2016 EDITION (foreword, Clauses 1–6, Figures 1–3). The standard was prepared by ISO/TC 35 "Paints and varnishes", subcommittee SC 9 "General test methods for paints and varnishes"; the third edition replaced ISO 4628-2:2003 and changed: a) a normative reference to ISO 13076 on lighting during assessment was added, b) a note on the visibility of blisters of size S1 was added. According to its foreword the 2003 edition (the second) was mainly an editorial revision of the 1982 edition — the pictorial standards were replaced by computer-generated images, and binary images for the calibration of optical systems were added. The ISO 4628 series: part 1 — general principles and designation system, 2 — blistering, 3 — rusting, 4 — cracking, 5 — flaking, 6 and 7 — chalking by the tape method and by the velvet method, 8 — delamination and corrosion around a scribe, 10 — filiform corrosion. Definition (3.1): degree of blistering is the assessment of blisters in a coating with regard to their quantity (density) and size. Assessment (Clause 4): the quantity and size of blisters are assessed according to Figures 1–4; NOTE — blisters of size S1 are not visible with normal corrected vision, only at ×10 magnification; if the test area has blisters of different sizes, the size of the blisters typical of the area is given; the assessment is carried out in good lighting according to ISO 13076; when an optical imaging system is used, it is calibrated with the images of Annex A. Expression of results (Clause 5): the quantity (density) and size of blisters according to Figures 1–4, together with the approximate dimensions of the area evaluated or its share of the whole surface in percent — e.g. a coating with blisters of quantity 2 and size 2 (Figure 1 a)) is recorded as "blistering; degree of blistering 2(S2)". Report (Clause 6): identification of the coating, reference to ISO 4628-2, type of surface tested, its size and location, result according to Clause 5, lighting, any deviations noted and the date of the test. Figures 1–3 show blisters of sizes 2, 3 and 4 in quantities 2, 3, 4 and 5 — designations from 2(S2) to 5(S4).

STATUS (state of the card on 30 September 2026). The card of PN-EN ISO 4628-2:2016-03 (English version) has no "Withdrawn" header — the standard is CURRENT: published 08-03-2016, 24 pages, price group M, Chemistry Sector, KT 175 for Paints and Varnishes, ICS 87.040, "Introduces: EN ISO 4628-2:2016 [IDT], ISO 4628-2:2016 [IDT]", "Replaces: PN-EN ISO 4628-2:2005 - Polish version". PKN search for "PN-EN ISO 4628-2" (30 September 2026): PN-ISO 4628-2:1999 — "Withdrawn and replaced by PN-EN ISO 4628-2:2004 - English version", that one — "Withdrawn and replaced by PN-EN ISO 4628-2:2005 - Polish version", and that in turn — "Withdrawn and replaced by PN-EN ISO 4628-2:2016-03 - English version", which carries no label.

HOW MANY LABORATORIES AND IN WHAT FORM (copy of the accreditation-scope database, data loaded up to 17 September 2026, read on 30 September 2026). 10 records at 10 laboratories — the same number of cells in the current PCA documents. The notation "PN-EN ISO 4628-2:2016-03" — 6 laboratories (AB 089, AB 163, AB 1424, AB 1552, AB 1631, AB 1700), without a year — 4 (AB 023, AB 128, AB 369, AB 910). The "Laboratories" tab looks for notations that BEGIN with "PN-EN ISO 4628-2" and will show all 10 laboratories — checked with the tab's query on the production server labcoda.pl on 30 September 2026: 10. Current scopes on the PCA website (read on 30 September 2026, issues from 16.07.2025 to 01.09.2026): the entries with this standard are not suspended (AB 1700 has another part of its scope suspended).

QUANTITY AND ITEMS. Assessment of the degree of blistering alone — AB 089, AB 1424, AB 1552, AB 1631, and AB 023 "blistering, also in situ"; blistering as one of the characteristics in the evaluation of degradation of coatings — AB 128 (together with ASTM D714), AB 163 and AB 369 (with parts 1, 3, 4, 5, 6 and 8 of the series), AB 1700 (with parts 1, 3, 4, 5 and 10); AB 910 — in an entry for corrosion resistance in salt spray, together with PN-EN ISO 9227 and PN-EN ISO 10289. Items: paint, varnish, organic and inorganic coatings, paint systems and anticorrosion coatings, as well as products of metal, plastics and composites, builders' hardware and parts of machines and equipment (AB 1552). The entries have no numerical ranges.

ALONGSIDE THIS STANDARD. The same entries include: PN-EN ISO 4628-1 — the designation system (AB 163, AB 1552, AB 1700 with the year 2016-03, AB 369 without a year), other parts of the series (AB 163, AB 369, AB 1700) and ASTM D714 — at AB 128; according to the table of contents, Annex B of the standard (informative) gives the relationship between the scales of ISO 4628-2 and ASTM D714. The salt spray test according to PN-EN ISO 9227 has a separate entry in the Knowledge Base. "Blisters" in another sense — resistance of bitumen shingles to blistering according to PN-EN 544 (AB 008), the bubble emission method of leak testing according to PN-EN 1593 (8 laboratories) or blisters in the insulation of pre-insulated pipes — are other quantities, not the degree of blistering of coatings.

WHERE A SEEMINGLY CORRECT RESULT IS EASY TO GET. First — lighting: since the 2016 edition the assessment is carried out in lighting according to ISO 13076, and the report must state it — a result without it is incomplete. Second — size S1: blisters of size S1 cannot be seen with the naked eye, only at ×10 magnification — "no blistering" assessed without a magnifier does not exclude S1. Third — blisters of different sizes: the size typical of the area is given, not the largest or the smallest. Fourth — area evaluated: a degree of blistering without the size of the area evaluated or its percentage share cannot be compared between specimens. Fifth — scales: an assessment according to ASTM D714 (AB 128) uses a different scale; the conversion between the scales is given in Annex B, whose content we do not know. Sixth — optical system: assessment with an image analyser requires calibration with the images of Annex A.

WHAT WE DO NOT GIVE. The sample ends at Figure 3: we do not give Figure 4 (blisters of size 5), the calibration images of Annex A, the relationship between the scales of Annex B or the definitions of the quantity and size scales from ISO 4628-1 (apart from the note on size S1).

Method principle

Blisters in the coating are compared with the pictorial standards (Figures 1–4) showing blisters of sizes 2–5 in quantities (densities) 2–5, and a degree of blistering is assigned in the form "quantity(Ssize)", e.g. 2(S2), together with the size of the area evaluated. The assessment is carried out in good lighting according to ISO 13076; when an optical imaging system is used, it is calibrated with the images of Annex A.

Applications

• Paint, varnish, organic and inorganic coatings, paint systems and anticorrosion systems — in the scopes of 10 laboratories
• Evaluation of the degradation of coatings after ageing and corrosion tests, e.g. after the salt spray test (AB 910)

Key parameters

Standard

Standard number

PN-EN ISO 4628-2:2016-03 (wersja angielska; EN ISO 4628-2:2016, ISO 4628-2:2016 IDT)

Title (PL)

Farby i lakiery — Ocena zniszczenia powłok — Określanie ilości i rozmiaru uszkodzeń oraz intensywności jednolitych zmian w wyglądzie — Część 2: Ocena stopnia spęcherzenia

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 2: Assessment of degree of blistering

Step-by-step procedure

1. Preparing the assessment

   Define the test area and its dimensions (or its share of the surface); provide lighting according to ISO 13076. PN-EN ISO 4628-2:2016-03 current (state of the card on 30 September 2026).

2. Comparison with the pictorial standards

   Compare the blisters with Figures 1–4; with different sizes take the size typical of the area; check S1 at ×10 magnification.

3. Recording the result

   "Blistering; degree of blistering quantity(Ssize)", e.g. 2(S2), with the dimensions of the area or its share in %.

4. Report

   Identification of the coating, reference to ISO 4628-2, type and size of the surface, result, lighting, deviations, date of the test.

Required equipment and apparatus

Health and safety (OHS)

• Visual assessment without particular hazards — rules for handling specimens after corrosion and ageing tests
• SUBSTANTIVE NOTE: without the lighting and the size of the area evaluated the result is incomplete; size S1 requires ×10 magnification

Frequently asked questions