ISO 4628-6:2011 pdf 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 6: Assessment of degree of chalking by tape method.
5 Procedure 5.1 Allow the surface to dry at room temperature before carrying out the test. Place a piece of the adhesive tape (4.1) on the dry coating by applying firm pressure and rubbing with a finger. The length of the tape should be at least 40 mm. Remove the tape perpendicularly to the surface and lay it on a background (4.2) of the appropriate colour to give the greater contrast, with the adhesive in contact with the background. Assess light-coloured coatings on the black background and dark-coloured coatings on the white background. Under consistent illumination, immediately assess (see 5.5) the degree of chalking by comparing the amount of chalk on the tape with the pictorial reference standards in Figure 1. The more background that is visible, the lower the rating. Report the illumination in the test report. 5.2 The degree of chalking may also be determined quantitatively using a suitable photoelectric instrument to compare the transmittance of the chalked tape with that of unused tape. In this procedure, the adhesive tape shall not be placed on a background (4.2) but on a clean glass slide or open support, which is placed in the optical beam of the instrument [2],[3] . A transmittance of less than 70 % of that of the unused tape indicates chalking. This instrumental method shall only be used if the pattern of chalking residues on the tape is homogeneous. 5.3 The degree of chalking can vary over a given area. On large areas with a uniform surface (no texture), the determination should preferably be made at several locations and the mean and range reported. Apply the tape to an area of the panel that has not been used for previous measurements to avoid false readings. 5.4 Ratings obtained with coatings exposed to natural weathering shall be treated with caution as dirt deposited on the surface from the atmosphere can give false values of chalking.