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.
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