The effects of exposure to humid conditions in the extended cataplasm ageing test, based on ISO 9142, Procedure E2 on the mechanical properties of adhesively bonded joints, were investigated as a part of a comprehensive study on the ageing of an acrylate adhesive and a Silane-terminated polymer (STP) adhesive. The adhesives were applied in aluminium and Zn-electroplated steel substrates with various surface treatments (a smooth surface, a roughened surface, andanodized and blank aluminium) to observe the effect of ageing on joints with various substrates. The predominant effect of high relative humidity in the cataplasm test was compared with the results of immersion in water according to ETAG 002. It is shown that both ageing methods had a significant degrading effect on bond strength, on stiffness, and on the failure mode. However, water immersion had a more serious effect on the acrylate adhesive, especially in anodized aluminium joints, and the cataplasm test caused slightly greater worsening of the adhesive properties of STP.