ISO 4628-4:2016

Overview

ISO 4628-4:2016 - Paints and varnishes - Assessment of degree of cracking specifies a standardized, visual method for evaluating cracking in organic coatings. The method uses comparison with pictorial standards to designate the quantity, size and depth of cracks as part of the broader ISO 4628 series on evaluation of coating degradation. The standard supports consistent, repeatable visual inspections for ageing- and weathering-related failures.

Key topics and requirements

• Assessment method: Degree of cracking is assessed by direct visual comparison with pictorial reference figures (no instrumentation required).
• Quantity (density) rating: Scale 0–5 (0 = none; 1 = very few; 2 = few; 3 = moderate; 4 = considerable; 5 = dense pattern).
• Size rating: Scale 0–5 based on visibility and width:
  • 0 = not visible under ×10 magnification
  • 1 = only visible under magnification up to ×10
  • 2 = just visible with corrected vision (up to 0.2 mm)
  • 3 = clearly visible (larger than 0.2 mm up to 0.5 mm)
  • 4 = large (0.5 mm to 1 mm)
  • 5 = very large (generally >1 mm)
• Depth classification: Three main types:
  • a) surface cracks (do not fully penetrate topcoat),
  • b) cracks penetrating topcoat only,
  • c) cracks penetrating whole coating system.
• Lighting: Assessments must be carried out under appropriate illumination - normative reference to ISO 13076 (lighting and procedure for visual assessments).
• Reporting format: Numerical ratings and depth expressed together (example: "cracking; degree of cracking 2(S3)b") and include area or percentage affected.
• Test report content: Must identify the coating, reference ISO 4628-4, surface type and size/location, results, illumination used, anomalies, and date.

Applications

• Quality control and acceptance testing of painted surfaces after lab or field exposure
• Failure analysis and root-cause investigations for cracking and weathering
• R&D and comparative testing of coating formulations and protective systems
• Contract specification, inspection and handover reporting for building, marine, and industrial coatings
• Standardized documentation for procurement, certification and regulatory compliance

Who uses this standard

• Paint and varnish manufacturers and formulators
• Coatings laboratories and test houses
• Specifiers, architects and asset owners
• Inspectors, coating applicators and maintenance contractors
• Certification bodies and quality assurance teams

Related standards

• ISO 4628-1 (general designation system for coating defects)
• ISO 13076 (lighting and procedure for visual assessments)
• Other parts of ISO 4628 (blistering, rusting, flaking, chalking, delamination, filiform corrosion)

Keywords: ISO 4628-4:2016, degree of cracking, coating degradation, visual assessment, pictorial standards, crack size rating, crack depth, paints and varnishes.