Properties and Benefits: Lath are thin strips of wood used as a key for lime plaster. When the plaster has failed the lath can be clearly seen. Sometimes the laths need replacing because Lath can deteriorate over the years due to insect infestation or rot, especially if modern less breathable plasters or paints have been applied. Oak is a popular choice of timber for the lath. Sawn lath is straighter with a less textured surface than split Lath and is best for repairing lathed walls.