A Preface
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The committee responsible for this document is ISO/TC 35, Paints and varnishes, Subcommittee SC 9, General test methods for paints and varnishes.

The second edition removes and replaces the first edition (ISO 4628-7:2003), which has been technically revised with the following changes:

a) Graphic reference standards for digital powder levels 1 to 5 have been copied from ISO 4628-6:2011;

b) Added normative reference to ISO 13076 for assessing lighting.

ISO 4628 consists of the following sections under the general heading Paints and varnishments – Assessment of coating degradation – designation of the number and size of defects, and the intensity of uniform changes in appearance:

— Part 1: General introduction and specifying the system

— Part 2: Assessment of the degree of foaming

— Part 3: Assessment of the degree of rust

Part 4: Evaluation of the degree of cracking

— Part 5: Assessment of the degree of peeling

— Part 6: Assessing the degree of chalking by the tape method

— Part 7: Assessing the degree of chalking by the velvet method

— Part 8: Assessing the degree of delamination and corrosion around marking or other artificial defects

— Part 10: Assessment of the degree of filamentous corrosion

ISO 4628-7-2016 – Assessment of ageing of lacquers and varnish coatings – Assessment of the number and size of defects and the intensity of uniform changes in appearance – Part 7: Assessment of the powder grade by the velvet method

1 Scope
This part of ISO 4628 specifies a method particularly suitable for assessing the degree of chalking of white or coloured outer coatings on rough surfaces and coating systems (i.e. coatings with roughness greater than that of the reference comparator section G 4 as described in ISO 8503-1).

The specified test method can also be used to assess the degree of pulverization of coatings and coating systems on smooth surfaces, but for this purpose the method specified in ISO 4628-6:2011 is preferred.

The test method is applicable to paints and coating systems on mineral substrates, such as fiber cement, brick, concrete, and rendering, independent of surface structure. The method can be used very effectively by experienced operators and is recommended for laboratory and field evaluation.

Note 1 When a reference to the test method is included in the specification, the test conditions (i.e. the aging method and the substrate) need to be agreed upon between the interested parties.

Note 2 The method described in this part of ISO 4628 is a relative ranking method and is therefore not suitable for use in agreements between parties. But see the description of Table 1.

Note 3 For the number and size of defects, the intensity of changes in the appearance of the coating and the general principles of the system, please refer to the specified system of ISO 4628-1.

2 Normative references
The following documents are referred to normatively in whole or in part in this document and are required for their application. For dated references, only the cited version applies. For undated references, the new version of the reference (including any revisions) applies.

ISO 13076, Paints and varnishes – Lighting and procedures for visual assessment of coatings

ISO 4628-7-2016 – Assessment of ageing of lacquers and varnish coatings – Assessment of the number and size of defects and the intensity of uniform changes in appearance – Part 7: Assessment of the powder grade by the velvet method

3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.

3.1 Pulverization

A loosely adhered fine powder appears on the surface of the film, which results from the degradation of one or more components

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