A zig-zag pattern of rotationally welded dowels across the interface of a butt joint between two wood planks was shown to yield strong joints without any adhesive. Tests after 2 h in boiling water showed that the joints were able to resist both 2 h immersion in boiling water, as well as the subsequent oven drying. Some unusual densification patterns were observed by X-ray microdensitometry. X-ray microdensitometry analysis of densification patterns in the dowel and at the dowel/substrate interface indicate that further improvement and optimisation of this process should consider minimizing the compression rate at the end of dowel rotation as well as minimization of the insertion impact of the dowel to avoid interfacial microfissures that can sometimes develop.