AbstractA series of nondestructive and destructive tests were performed on samples of aluminumto-aluminum bonded plates. The specimens featured a range nominal thickness of the adhesive layer from 0.0 up to 0.5 mm. It was found that a commercial bondtester was inappropriate for assessing the thickness of the adhesive in this range. However, the frequency peak of an ultrasonic echo signal from the adhesive layer was a reliable indicator of bond thickness. It is proposed that nondestructive assessments of the bond thickness could serve as an indicator of the longterm resistance of the adhesive to water ingress and bond degradation.