A system for joining and adhering a pair of abutting panels to a rigid substrate and providing a seal against thermal and moisture transfer. The system is comprised of an elongated receptacle member with a base and a pair of spaced vertical elements extending upwardly from the base and forming a channel, to be placed under and between edges of the panels to be joined. The receptacle member is firmly attached to the rigid substrate by fastening means passed through the base. The adjacent side walls of the vertical elements include a plurality of vertically spaced, downwardly angled teeth projecting inwardly towards the center of the channel. An elongated resilient insert member includes a cap and a projection extending downwardly from said cap. The opposed side wall surfaces of the projection include a plurality of vertically spaced, upwardly angled teeth projecting outward from said projection a sufficient distance to engage the downwardly angled teeth of the receptacle member when the projection is inserted in the channel. The cap of the insert member has a convex upper surface and a concave lower surface so that when the projection of the insert member is inserted in the receptacle member, the resilience of the cap exerts a slight upward force on the projection providing a positive engaging force that tends to lock the projection in the receptacle member. A layer of adhesive-sealant is attached to the lower concave surface of the cap on each side of the projection and is disposed to contact and seal the cap to the panels to be joined.