ISO 4628-4:2016 pdf free download.Paints and varnishes — Evaluation of degradation of coatings — Designation of quantity and size of defects, and of intensity of uniform changes In appearance — Part 4: Assessment of degree of cracking.
1 Scope
This part of ISO 4628 specifIes a method for assessing the degree of cracking of coatings by comparison with pictorial standards.
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.
2 Normative references
The following documents, in whole or In part, are normatively referenced in ISO 4628-4 and are indispensable for its application. For dated references, only the edition cited applies. For undated references, the latest edition of the referenced document (Including any amendments) applies
ISO 13076, Paints and varnishes — Lighting and procedure for visual assessments of coatings
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
3.1
degree of cracking
rating characterizing cracks in a coating in terms of quantity, size, and depth
4 Assessment
Assess the quantity of cracking by reference to Table 1. and using as example jggJ. or Figure 2. depend ing on the type of cracking.
NOTE Figure 1 shows cracking without preferential direction and Figure 2 shows cracking in one preferential direction, which occurs with substrates such as wood (anisotroplc” substrates). Other forms of cracking occur, but the principles of assessing the quantity remain the same.
Where the test area exhibits cracks of various sizes, quote as the size rating that of the largest cracks which are numerous enough to be typical of the test area.
If possible, indicate the depth of cracking by reference to the level in the coating system to which the cracks penetrate. A distinction is made between three main types of failure by cracking:
a) surface cracks which do not fully penetrate the top coat (i.e. checking);
b) cracks which penetrate the top coat, the underlying coat(s) being substantially unaffected;
c) cracks which penetrate the whole coating system.
Carry out the assessment under good illumination, as specified In ISO 13076.
5 Expression of results
Express the numerical ratings of the quantity and, if specified, size of the cracks, together with the depth of cracking (a, b, or c), shown in Figures 1 and Z together with the approximate dimensions of the area concerned, or its proportion to the total area, expressed as a percentage.
For example, for quantity 2, size 3 with the cracks penetrating the top coat and the underlying coat(s) are substantially unaffected, report the result as
— cracking; degree of cracking 2(S3)b.
If necessary, the assessment may he amplified in words, for example cracking in one preferential direction and by using the descriptions given in Annex A.
6 Test report
The test report shall contain at least the following information:
a) all details necessary to identify the coating examined;
b) a reference to this part of ISO 4628, i.e. Iso 4628-4;
c) the type of surface examined, Its size and. If appropriate, its location;
d) the result of the examination in accordance with c1ause.5;
e) an indication of the illumination under which the assessment was carried out;
f) any unusual features (anomalies) observed during the assessment;
g) the date of the examination.