Abstract: Joining together two materials by a mechanical interlock resulting from "chips" at their interface is disclosed. The chips, composed of one of the two materials to be joined or of a third material are partially embedded into the surface of the first material when that material is formed so as to form surfaces which "overhang" the first material. Thereafter, the second material is formed against the overhanging surfaces of the chips to establish the mechanical interlock. This technique is particularly useful in anchoring a dissimilar material to a polymeric material having poor bondability and/or a high melt temperature, for example fluoropolymers, as illustrated by the forming of a liner for a pump casing, or the like, by rotational molding.