Embodiment of a disclosed seam tool (10) comprises a rigid backing configured to be positioned about a seam region (24) defined by at least two adjacent pattern segments (12, 14). The rigid backing further includes an injection port (20) and, typically, a gas outlet port (22), fluidly coupled to the seam region. The disclosed device may further include a resilient liner (54) which contacts and forms a seal with surfaces of the pattern segments. Compensating grooves may be formed in the resilient material to allow complete filling of the seam region by weld-forming material. An injection fitting may be operably coupled to an injection port to provide an improved ability to receive weld-forming material to form welds. A method for forming a weld between plural, adjacently positioned pattern segments also is disclosed. The method comprises positioning the disclosed embodiments of the seam tool about a seam region defined between adjacent pattern segments.