Lath

A lath or slat is a thin, narrow strip of straight-grained wood used under roof shingles or tiles, on lath and plaster walls and ceilings to hold plaster, and in lattice and trellis work.

Lath has expanded to mean any type of backing material for plaster including a metal wire mesh or expanded metal that is applied to a wood or metal framework as matrix over which stucco or plaster is applied and wallboard products called gypsum or rock lath. Also reed mat was historically a lath material. One of the key elements of lath, whether wooden slats or wire mesh, are the openings or gaps that allow plaster or stucco to ooze behind and form a mechanical bond to the lath where gypsum lath relies more on a chemical bond.

The word is recorded from the late 13th century and is likely derived from the Old English word *læððe, a variant of the word lætt. This in turn would seem to stem from a Proto-Germanic word *laþþo, from which have sprung words in many Germanic languages, e.g. Dutch lat, German Latte; the root has also found its way into Romance languages, cf. Italian latta, French latte, and is related to German lade, laden denoting a board, plank, sash, shutter, counter and hence also a shop.

Gypsum lath (rock lath) consists of gypsum plaster sandwiched between two sheets of absorbent paper, the finish side treated with gypsum crystals for the plaster to chemically bond to and sometimes perforated to allow mechanical bonding. It was improved in 1910 by the paper wrapping the edges and multiple variations were developed in the 1930s. Gypsum lath is commonly used in place of wood since it is noncombustible, easy to use, and gives better results. The popularity of the lath and plaster method declined in the 1950s, as it was replaced by the less expensive drywall method. Gypsum lath is available with a foil facing which acts as a vapor barrier and heat reflector, and as a veneer base for plaster veneer.

...
Wikipedia