Lath is the system of components that secure mortar to the supporting structure by means of a mechanical bond. The primary functions of stucco lath are to provide perimeter alignment for the stucco membrane, and an interlock between the supporting structure and the stucco mortar. Stucco lath must be able to receive and support fresh stucco mortar, and provide reinforcement for the first mortar application. Ideally, lath and stucco mortar combine to form an integral unit. This unity depends on the type and effectiveness of the bond between the two systems.

A mechanical bond is obtained by a process involving characteristics of the mortar as it changes from to a hardened state. Upon application, the stucco mortar completely encases and clings to the lath. As it hydrates the mortar slowly hardens around the lath, eventually resulting in the formation of permanent keys. The internal support provided by the embedded lath serves to increase the strength of the resulting stucco membrane.