Linear vibration welding of good quality pine (Pinus sylvestris) wood from Sweden containing a small proportion of a native mixture of terpenoic acids, known under the collective name of rosin, has been shown to yield joints of much upgraded water resistance. This has been shown to be due to the protecting influence the molten rosin from the wood itself has on the welded interphase, because of the water repellency of rosin. Joints of unusually high percentage wood failure but modest strength were obtained, rosin apparently reinforcing the welded interphase to yield weldline strengths always much higher than the strength of the surrounding wood. (C) Koninklijke Brill NV, Leiden, 2011.