This part of ISO 4628 describes a method suitable, in particular, for rating the degree of chalking on white or coloured exterior coatings and coating systems on rough surfaces (i.e. those having a roughness greater than segment 4 of reference comparator G as described in ISO 8503-1).
The test method specified may also be used for the assessment of the degree of chalking of coatings and coating systems on smooth surfaces, but the method specified in ISO 4628-6 is preferable for this purpose.
The test method is applicable to coatings and coating systems on mineral substrates, e.g. fibre cement, brick, concrete and renderings, independent of the structure of the surface. The method can be used quite effectively by experienced operators and is recommended for laboratory use as well as for on-site evaluation.
NOTE 1 When a reference to this test method is included in specifications, the test conditions (i.e. weathering method and substrate) should be agreed 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. See, however, the Note to Table 1.
ISO 4628-1 defines the system used for designating the quantity and size of defects and the intensity of changes in appearance of coatings and outlines the general principles of the system. This system is intended to be used, in particular, for defects caused by ageing and weathering, and for uniform changes such as colour changes, for example yellowing.