Abstract: Method and apparatus for patching or seaming thermoplastic mesh fabrics, such as used in the papermaking industry by means of an ultrasonic welding tool. The tool is provided with one or more tips having raised surface portions or projections adapted for contacting the plastic mesh at a plurality of spaced points whereby ultrasonic welding is accomplished without substantial disruption or dimunition of the generally uniform porosity inherent to the mesh fabric. The method modifications involve the use of templates for guiding the positioning and movement of the ultrasonic welding tips for both butt seaming and overlap seaming of the opposed edges of thermoplastic mesh fabric. In the butt seaming technique, the outermost weft filaments of the opposed edges of the plastic fabric are replaced by one heat stabilized filament and the picket ends of the fabric are interdigitated about this stable filament preparatory to the welding step.