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EN 302-1 and EN 205 are among the most commonly used standards for the approval as well as research of wood adhesives to evaluate bond strength. The present study investigates the sensitivity of the lap-joint samples to a possible error in groove cutting as well as the influence of using steam-treated and untreated beech wood on tensile shear strength. The lap-joint specimens cut with 0.5 mm too shallow and 0.5 mm too deep grooves was compared with samples cut precisely within the tolerances mentioned in the standards. A comparison of tensile shear strength between the joints manufactured out of steam-treated and untreated beechwood has been made. The results show a significant influence of groove depth on the resulting tensile shear strength. While deep groves (+0.5 mm) underestimate, shallow grooves (−0.5 mm) overestimate it dramatically. Additionally, the joints with steam-treated beech wood delivered lower tensile shear strength than those of untreated beech wood bonds when there is a considerable wood failure percentage. When the ultimate tensile shear strength of the adhesive bond approaches the shear strength parallel to the grain of wood, the impact of steam-treated beech wood on the estimation of adhesive bond strength is higher. [ABSTRACT FROM AUTHOR]

Depending on the expected use of timber structures and wood-based panels jointed with adhesives, Eurocode/European standard defines various service classes for the design of buildings, where different moisture ranges might be expected. As a result, it can be assumed that the amount of moisture in the adherend has a significant impact on wood-adhesive bond lines. In-situ nanoindentation was used to investigate the influence of moisture on mechanical properties in service conditions for commonly used structural and non-structural wood adhesive systems (polyvinyl acetate adhesive PVAc, a flexible two-component melamine-urea-formaldehyde adhesive MUF, urea-formaldehyde adhesive intended for form pressing applications UF A, and particle board urea-formaldehyde adhesive UF B, and a phenol-resorcinol-formaldehyde adhesive PRF). The urea-formaldehyde adhesive intended for form pressing applications and PRF adhesives displayed better stability in elastic behaviour and very little change in creep behaviour at elevated relative humidities. The thermoplastic adhesive PVAc, particleboard urea-formaldehyde (UF A), and MUF adhesive systems with flexible thermoplastic components showed lower stability with increasing relative humidity levels above 66%. The two-component MUF adhesives showed increasing creep with increasing flexible second component at elevated relative humidities. The pre-polymerized adhesive PVAc turned out to be the most sensitive one to moisture. [ABSTRACT FROM AUTHOR]