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.

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