An attachment for a sewing machine to provide simultaneous sewing and sealing of a seam comprises a reel for dispensing a strip of adhesive thermoplastic polymer between fabric members to be sewn. A plurality of heated driven rollers opposed to heated idler rollers having a continuous belt thereover collectively exert heat and pressure on the seam, melting the polymer strip so as to seal the seam. Thread having been treated with adhesive thermoplastic polymer may be employed to seal the punctures in the fabric made by the sewing machine's needle. The driven rollers are driven in synchronization with the operation of the sewing machine, and are engaged with and withdrawn from the seam responsive to operator command.