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L-joint based testing for service life prediction of exterior plywood in out of ground contact conditions
2006 - IRG/WP 06-20342
Good biological performance of several plywood types in exterior conditions is most probably related to altered wood moisture behaviour compared to solid wood. Therefore a test set up was developed, using EN 330 L-joint testing methodology, to facilitate differentiation of plywood for exterior applications. The proposed test set up is an adaptation of an accelerated L-joint method introduced by Van Acker and Stevens (2003). Regular L-joints are used to expose plywood specimens as an infill window system. The L-joints simulate bottom corners of a low quality joinery unit. Accelerated testing is based on a moistening device using a drip irrigation system feeding a horticultural rock wool sponge as wetting agent. This keeps the lower corner of the plywood sample wet and creates a moisture gradient in the panel. The specimens are inclined for 10 degrees, the face veneer of the plywood is facing south and inclined 45°. The newly developed exposure method is intended to be severe and acts as a simulation of a worst case situation. The accelerated weathering makes differentiation among several plywood products possible after only one year of outdoor exposure. Visual appreciation of the tested plywood, mass loss measurements, alterations in moisture absorption and desorption patterns and isolations of fungi present on the samples help to rank plywood in view of fit for purpose for use class 3 exposure conditions.
J De Smet, I De Windt, J Van Acker


Service life prediction of plywood
2007 - IRG/WP 07-20367
Plywood is the wood based panel showing the best physical and mechanical properties for application under moist construction conditions. Appropriate physico-mechanical durability for exterior applications in transportation or construction systems can be guaranteed by assessment of the glue bond quality and mechanical characteristics. However, due to the fact that mainly non-durable wood species are used for plywood production, there is a need to specify the biological durability of plywood in relation to service life. With the European standard ENV 12038 a tool is available to evaluate the intrinsic biological durability of plywood material. According this standard plywood has to be tested against wood rotting basidiomycetes using a test procedure equivalent to the EN 113 procedure for the assessment of wood preservatives when testing of solid wood. Testing a large amount of different commercial plywood products according to this standard showed that the test procedure is too severe, offering no possibility to differentiate between panel types (e.g. the influence of a coating could not be distinguished). To be able to use the ENV 12038 as an aid for service life prediction the test procedure needs to be adapted and the results need to be linked to data collected during outdoor field testing. Service life prediction of plywood requires a combination of durability testing and evaluation of moisture related properties, and relates this to data collected during outdoor field testing and in service data (derived from e.g. surveys). Furthermore there is a need to identify a simple methodology to interrelate product properties and intended service life for different use class conditions. This paper suggests an approach to enable implementation in practice for plywood.
J Van Acker, J De Smet


Non-destructive monitoring of structure and moisture dynamics of plywood exposed outdoors to improve service life prediction and fit-for-purpose design
2015 - IRG/WP 15-20570
Plywood is an important construction material yet prone to water uptake, which can decrease strength and increase decay risk. To predict service life and improve fit-for-purpose design, it is crucial to understand the moisture behavior and structural changes of plywood. In this research, several plywood specimens were exposed outdoors for approximately one year. During this period, the moisture distribution in different layers of the exposed plywood specimens was monitored continuously and detailed field weather information was collected simultaneously. The internal structure of the specimens was also investigated by periodically scanning using 3D X-ray CT. The moisture distribution throughout the different plies is not always homogeneous. The second layer can accumulate a significant amount of water in outdoor weathering conditions, giving rise to high Time of Wetness (TOW) and long rainfall events can keep wetting the inner layers of plywood. TOW, moisture dynamics and wood species used are the main factors causing structural changes of the plywood veneers in service mainly occurring as cracks. Most internal structural changes were found in the second veneers of plywood specimens. The glue line between veneers can hardly be ruptured after exposing outdoors for one year. Plywood with veneers showing a slow water sorption and fast water desorption could effectively avoid internal moisture accumulation and cracks in service. Based on the knowledge of the relationship among weathering data, internal moisture behavior and structural changes in service, the dedicated plywood could be designed by optimizing the characteristics, i.e. veneer wood species, veneer thickness, glue type and such. The above knowledge could also contribute to the service life prediction of plywood.
W Li, J Van den Bulcke, I De Windt, M Dierick, J Van Acker


The registration of wood preservatives under the Pesticides Act of 1962 in the Netherlands
1976 - IRG/WP 364
J Van der Kolk