Expansion joints in the field of tile floors are essential and required to accommodate building movements and to prohibit cracks in the substrate from telegraphing to the tile finish. This detail illustrates the use of a prefabricated expansion joint profile strip. The perforated horizontal anchoring legs of the profile strip are fully embedded with a cementitious bond coat of adhesive mortar, anchoring the profile strip to the substrate. The movement zone between the vertical legs of the profile strip should be free and clear of mortar, allowing the gasket to expand as the tile expands. Bond breaker tape (not shown in the detail) may be used to keep the movement zone below the gasket free of mortar. The design professional specifies the width, locations, and frequency of field expansion joints.