Indentation and pendulum hardness tests: two convenient assessment methods of the performance of exterior wood coatings

IRG/WP 15-40689

L Malassenet, L Podgorski, M Truskaller, G GrĂ¼ll

Developing formulations of exterior wood coatings with long service life is a big challenge. For many years in Europe the performances have been mainly evaluated through weathering tests (within the EN 927 series) followed by visual assessment (blistering, flaking, mould growth, chalking and cracking), colour and gloss measurements, and adhesion tests. Very recently the importance of the mechanical properties of coatings has been taken into consideration within the CEN/TC 139/WG2 and a test method (CEN/TS 16360) has been suggested to assess the film extensibility by indentation of a coating on a wooden substrate. In 2014 this technical specification was added in the EN 927-2 standard. The aim of this work was to investigate this destructive indentation test for several commercial acrylic coatings applied on spruce and Scots pine. In addition, pendulum hardness tests were carried out as a non-destructive test to gain further information about mechanical properties of the tested coatings. The influence of thickness was examined. This work discusses the advantages and the limits of both methods. They allowed a discrimination of the coatings studied and gave a similar ranking for most of the coatings. The paper also shows the relationship between pendulum hardness variation and long-term performances. Indentation and pendulum hardness tests are shown as useful investigations in addition of the conventional assessment framework of exterior wood coatings.

Keywords: wood coating, film mechanics, performance, indentation, hardness, pendulum

Conference: 15-05-10/14 Vina del Mar, Chile

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