TECHNICAL STANDARD
ISO 4628-2
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
ISO
2016
Current
WHAT DOES THIS STANDARD COVER?
ISO 4628-2 specifies a method for assessing the degree of blistering of coatings using pictorial standards and the designation principles of the ISO 4628 series.
WHY IS IT RELEVANT?
Provides a recognised method for consistently recording blistering during coating condition surveys and failure investigations. The classification describes the observed defect; it should not by itself be treated as establishing the cause of blistering.
KEY INSPECTION CONSIDERATIONS
The standard addresses assessment of the degree of blistering of coatings. A consistent rating approach allows blistering condition to be documented and compared. Blistering can occur for different reasons, so the observed condition should be documented before conclusions are drawn regarding its cause.
WHAT THE STANDARD SHOULD NOT BE USED TO ASSUME
A blistering rating does not establish the root cause of blister formation. Visual assessment alone may be insufficient to determine whether deterioration is associated with moisture, contamination, coating application, substrate condition or another mechanism. The rating also does not independently establish the condition of the substrate beneath the coating.
PRACTICAL INSPECTION APPLICATION
During coating surveys or failure investigations, inspectors can identify affected areas, record the applicable blistering assessment and retain photographs and location information. Variations between areas should be documented. Other inspection or testing evidence can then be considered where the cause or significance of blistering needs to be investigated.
RELATED TECHNICAL STANDARDS
RELATED TECHNICAL TOPICS
Condition Assessment Blistering Coating Defects Coating Condition Survey Failure Investigation
RELATED PIL GUIDANCE
A pre-condition coating survey brings visual inspection, testing, sampling and access planning together to support evidence-based maintenance decisions.
A structured approach to investigating protective coating failure through evidence, testing, sampling and project-record review.
RELATED EXPERTISE
Condition Surveys Coating Inspection Testing & Analysis Technical Consultancy
ABOUT THIS TECHNICAL SUMMARY
Paint Inspection Ltd provides this information to help inspectors, engineers, asset owners and contractors understand the practical relevance of commonly referenced protective coatings standards. This page is PIL technical guidance and does not reproduce or replace the published standard. Users should refer to the current published standard, project specification, coating manufacturer requirements and other applicable contract documents when establishing project requirements or acceptance criteria.
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OFFICIAL STANDARD
PIL technical summaries are intended to explain the inspection relevance of industry standards and do not replace the published document.
STATUS AND SOURCE VERIFICATION
Standard number, edition, title and current publication status checked against the official ISO catalogue in September 2026.