Assessment of degree of chalking by velvet method

BS EN ISO 4628-7:2003 pdf free.Paints and varnishes- Evaluation of degradation of coatings一Designation of quantity and size of defects, and of intensity of uniform changes in appearance一 Part 7: Assessment of degree of chalking by velvet method.
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 outines 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 referenced documents are indispensable for the application of this document. For dated references, only the edition cited applies. For undated references, the latest edition of the referenced document (including any amendments) applies.
ISo 4628-1, Paints and varnishes一Evaluation of degradation of coatings一Designation of quantity and size of defects, and of intensity of uniform changes in appearance一Part 1: General introduction and designation system ISo 4628-6:1990, Paints and vamishes 一Evaluation of degradation of paint coatings 一Designation of intensity, quantity and size of common types of defect一Part 6: Rating of degree of chalking by tape method ISO 8503-1，Preparation of stee/ substrates before application of paints and related products一Surface roughness characteristics of blast-cleaned stee/ substrates 一Part 1: Specifications and definitions for ISo surface profile comparators for the assessment of abrasive blast-cleaned surfaces.
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
3.1 chalking appearance of a loosely adherent fine powder on the surface of a flm arising from the degradation of one or more of its constituents
4 Principle Loosely adherent powder is removed from the coating under test, using a suitable fabric. The degree of chalking is assessed with reference to a rating scale.
5 Materials
5.1 Fabric, as agreed between the interested parties, to rub against the surface being tested. Black wool felt, velvet and velveteen have proven particularly effective for light coatings and a white fabric for dark coatings.
6 Assessment Carry out the assessment in duplicate, unless otherwise agreed.
Using the index finger, press the fabric against the coating under test with firm pressure. Rotate the fabric once through an angle of 180. Remove the fabric and assess the degree of chalking under diffuse light by reference to the rating scheme given in Table 1.
A mechanical apparatus is preferred if comparative results are to be obtained; the coating may also be wiped once with the fabric.
Examples of plictorial standards for sessing the degree of chalking are glven in IsO 4628-6:1990, Figure 1.
The amount of powder may vary over a given area. Therefore, the test shall be carried out at an average location on the coating. On large surfaces, the assessment shall be made at several locations, and the mean and range reported.
Ratings obtained with coatings exposed to natural weathering shall be treated with caution, as dirt from the atmosphere deposited on the surface can give abnormally high values of the degree of chalking.
7 Test report
The test report shall contain at least the following information:
a) all details necessary to identify the coating tested;
b) a reference to this part of ISO 4628 (ISO 4628-7:2003);
c) the type of surface examined, its size and, if appropriate, its location;
d) the numerical rating of the degree of chalking in accordance with Clause 6 (mean value, range and number of assessments);
e) all details necessary to identify the fabric used;
f) whether the result was obtained using the index finger or a particular apparatus (details to be indicated);
g) details of any deviation from the procedure specified;
h) any unusual features (anomalies) observed during the assessment;
i) the date of the examination.BS EN ISO 4628-7 pdf free download. Assessment of degree of chalking by velvet method