Variation in coating hardness during the EN 927-6 weathering test: influence of pigmentation

IRG/WP 16-40739

L Podgorski, L Malassenet, C Reynaud

The objective of the SERVOWOOD project is to develop and establish European Standards that will facilitate the prediction of service life for exterior wood coatings. Within this project an extensive round robin exercise has been carried out by five partners to establish the repeatability and reproducibility of the EN 927-6 artificial weathering test. This round robin included the exposure of the Internal Comparison Product, a semi-transparent alkyd stain described in EN 927-3, as well as its unpigmented version. Previous studies have shown that Persoz hardness was a useful property to study performance of exterior wood coatings exposed to natural and artificial tests. In this work, in addition of conventional assessment such as cracking and gloss, the Persoz pendulum was used to study hardness variation of the two coatings versus exposure time (from 0 to 12 weeks). Results showed that the exposure led to an increase in hardness for both coatings. However when cracking developed a decrease in hardness was found as cracks probably induced frictional forces on the pendulum which slowed down. For the semi-transparent stain, pigments clearly limited the hardness increase which probably explains that no cracks were found. A slight decrease in hardness was observed for the semi-transparent stain at the end of exposure. It was attributed to the significant change of gloss which may also contribute to slow down the pendulum due to a change in the surface roughness.


Keywords: wood, coating, weathering, hardness, pendulum

Conference: 16-05-15/19 Lisbon, Portugal


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