ISO 4628 Determination of the amount and extent of defects and the intensity of uniform changes in appearance in coatings

The ISO 4628 standard, “ Paints and varnishes – Assessment of deterioration of coatings – Determination of the quantity and size of defects and the intensity of uniform variations in appearance,” published by the International Organization for Standardization (ISO), consists of the following sub-sections published under the same title:

ISO 4628-1 Part 1: General Identification and Identification System describes a system for determining the amount and extent of defects and the intensity of changes in the appearance of coatings and outlines the general principles of the system used throughout the ISO 4628 series of standards. This system is specifically designed for defects resulting from aging and weathering, and for uniform changes such as yellowing. Other sections of this standard provide pictorial standards or other tools for assessing specific types of defects. Wherever possible, existing assessment schemes have been used as the basis. This standard is also used to assess defects not covered by other sections.

This standard adopts a uniform convention for determining the quantity and extent of defects and the intensity of changes by rating on a numerical scale ranging from 0 to 5. "0" indicates no defects or changes, while "5" indicates defects or changes so severe that further discrimination is unreasonable. Other ratings are defined to provide optimal discrimination across the entire range of the scale. Intermediate half-steps are permitted, if specified, to provide a more detailed report of observed defects or changes.

The amount of small defects distributed over the test area can be assessed using a grid method. Details of such a method are described in ISO 10289.

ISO 4628-2 Part 2: Assessment of the degree of blistering describes a method for assessing the degree of blistering of coatings by comparison with pictorial standards. The pictorial standards provided in this section show blisters of sizes 2, 3, 4, and 5, with each size having a density (density) of 2, 3, 4, and 5. ISO 4628-1 defines the system used to describe the amount, size, and intensity of changes in the appearance of coatings and outlines the general principles of the system. This system is designed to be used specifically for smooth changes, such as defects resulting from aging and weathering, and color changes such as yellowing.

For the purposes of this standard, degree of blistering refers to the rating that characterizes the bubbles in a coating in terms of quantity (density) and size.

ISO 4628-3 Part 3: Assessment of the degree of rusting describes a method for assessing the degree of rusting of coatings by comparison with pictorial standards. The pictorial standards provided in this section show coated steel surfaces deteriorated to varying degrees by a combination of through-the-coating rust and visible under-rust.

The illustrated standards are selected from the European rust scale published by the Confederation of European Paint, Printing Ink and Artist Colour Manufacturers' Associations. The correlation between the ISO scale and the European rust scale is shown in the table in the appendix to the standard (Appendix B).

For the purposes of this standard, degree of rust refers to the degree that describes the extent of rust formation (rust break-up and visible sub-rust) in a coating.

ISO 4628-4 Part 4: Assessment of the Degree of Cracking describes a method for assessing the degree of cracking in coatings by comparing them with pictorial standards. ISO 4628-1 describes the system used to determine the amount and extent of defects and the intensity of changes in the appearance of coatings and outlines the system's general principles. This system is designed to be used specifically for defects resulting from aging and weathering, as well as for uniform changes in color, such as yellowing.

For the purposes of this standard, degree of cracking refers to the grading that characterizes cracks in a pavement in terms of quantity, size and depth.

ISO 4628-5 Part 5: Assessment of the Degree of Flaking" describes a method for assessing the degree of flaking of coatings by comparing them with pictorial standards. ISO 4628-1 describes the system used to determine the amount and size of defects and the intensity of changes in the appearance of coatings and outlines the general principles of the system. This system is designed to be used specifically for defects resulting from aging and weathering, as well as for uniform changes in color, such as yellowing.

For the purposes of this standard, degree of flaking refers to the gradation that characterizes the flaked areas in a coating in terms of quantity, size and depth.

ISO 4628-6 Part 6: Assessment of the degree of chalking by the tape method provides pictorial reference standards for determining the degree of chalking of paint coatings. It also describes a method for grading the degree of chalking. When using this method, it is important to be careful to distinguish between true degradation products and adhering dirt, especially when chalking is light.

For the purposes of this standard, chalking refers to the appearance of a fine powder loosely adhering to the surface of a paint coating, resulting from the deterioration of one or more of its components.

Chalking is removed from the coating being tested using adhesive tape. Chalking adhered to the tape is examined against a contrasting background (black or white, whichever provides greater contrast), and the degree of chalking is assessed using a grading scale.

ISO 4628-7 Part 7: Assessment of the degree of chalking by the velvet method describes a suitable method for assessing the degree of chalking on coating systems, particularly those on white or colored exterior coatings and on rough surfaces. The test method described can also be used to assess the degree of chalking on coatings and coating systems on smooth surfaces, but the method specified in ISO 4628-6 is preferred for this purpose.

The test method is applicable to coatings and coating systems on mineral substrates, such as fiber cement, brick, concrete, and plaster, regardless of the surface structure. This method can be used effectively by experienced operators and is recommended for laboratory use and on-site evaluation.

Loosely adhering dust is removed from the coating under test using a suitable cloth. The degree of chalking is assessed using a grading scale.

ISO 4628-8 Part 8: Assessment of the degree of delamination and corrosion around a scratch or other artificial defect on a coated panel or other coated test specimen caused by a corrosive environment describes a method for assessing delamination and corrosion around a scratch or other artificial defect on a coated panel or other coated test specimen. This section does not cover the assessment of pitting corrosion or pitting depth. Examples of corrosive environments include artificial atmospheres such as salt spray, used in the test method specified in ISO 9227, and seawater immersion, used in the test method specified in ISO 15711. Natural environments can also be used. The extent of other defects can be determined simultaneously with delamination and corrosion. The methods are as follows:
- Bubbling (according to ISO 4628-2 standard)
- Rust (according to ISO 4628-3 standard)
- Cracking (according to ISO 4628-4 standard)
- Exfoliation (according to ISO 4628-5 standard)
- Filiform corrosion (according to ISO 4628-10 standard)

In principle, delamination around a scratch or other artificial defect is assessed directly at the end of the test period, immediately after the test panel has been removed from a previous conditioning environment, or after a specified period of conditioning. Corrosion around the scratch or other artificial defect is assessed immediately after the test panel has been removed from a previous conditioning environment or after the coating has been removed. Both the degree of delamination and the degree of corrosion are determined by measurement and calculation.

The standard “ISO 4628-9 Part 9: Evaluation by image processing” has not been published yet.
ISO 4628-10 Part 10: Assessment of the Degree of Filiform Corrosion describes a method for assessing the extent of filiform corrosion developing from a scratched mark by measuring the longest filament and the most frequent filament length. The pictorial examples provided in the appendix to this section illustrate the various gradations of the longest filament and the most frequent filament length (Annex A). Comparison of test panels with the illustrations in Annex A does not invalidate the mandatory numerical assessment (Methods 1 or 2). ISO 4628-1 applies to the system of identifying the amount and size of defects and the intensity of changes in the appearance of coatings, and to the general principles of the system.

For the purposes of this standard, filiform corrosion refers to the type of corrosion that progresses in the form of threads beneath a layer of paint, varnish or related product, usually starting from bare edges or local damage to the coating.

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