This invention relates to an apparatus and method for joining fabric, particularly for joining separate pieces of layered fabric, by means of waterproof seam in a single operation. The seam bonding apparatus comprises a hot-melt adhesive supply (20), a transducer (24) which supplies ultrasonic energy and a sonotrode (23) which directs the ultrasonic energy to an application point on the seam to be bonded. Adhesive, preferably molten nylon, is fed through a passage (25) in the sonotrode (23) via an exit aperture (28) at the end of the sonotrode to the application point. Local heat is applied to the other side of the seam at the application point, and the seam is then subjected to local cooling to form a permanent waterproof seam.