Wood Lath

Plaster over wood lath was used approximately between 40 to 120 years ago.  Application includes the wood lath and three coats of cement and plaster materials. The wood lath was about 3/8 inch thick and about 1 1/2 inches wide.  It was nailed across the wood studs and had spaces of about 1/4 inch between each piece, which acted as a keyway for the first coat of the plaster to ooze through and attach to the lath.  This first coat is called the ground (or scratch) coat.  The second coat is the same material, and is called the brown or scratch coat. The third or final coat is a hard coat plaster, and is called the finish coat.  The ground and scratch coats are each 1/4 inch to 3/8 inch thick. The finish coat is about 1/8 inch thick.  Well maintained home with plaster and wood lath walls are usually dependable for 100 to 120 years or more.

Plaster and wood lath ceilings may experience cracking as the system ages.  The ceilings may crack in one direction after 35 to 45 years.  Larger ceilings/rooms typically crack before smaller ceilings. Between 45 and 60 years, cracks perpendicular to the first cracks may develop.  Between 70 to 80 years, sections of some ceilings are likely to separate from the lath.  After 80 to 100 years, many of the plaster ceilings may need replacement or significant repairs.