What is the difference between 'lath and plaster' and 'plaster over gypsum board'?

• A. Lath and plaster uses gypsum board backing; plaster over gypsum board uses lath backing.
• B. Lath and plaster uses lath backing; plaster over gypsum board uses gypsum board backing with veneer plaster.
• C. Both methods use gypsum board backing with veneer plaster.
• D. They are the same technique with identical backing.

Answer: (B)

The difference comes down to the backing and how thick the plaster coating is. In traditional lath and plaster, plaster is applied over a framework of lath (wood or metal) that provides a rough surface for the plaster to key into, and the plaster is built up in multiple coats to create a thick, durable wall. In plaster over gypsum board, the backing is gypsum board (sheetrock) and a veneer plaster coat is applied on top as a thin final skin, resulting in a lighter system that relies on the gypsum board as the substrate.

That’s why the statement that matches reality is: lath and plaster uses lath backing; plaster over gypsum board uses gypsum board backing with veneer plaster. The other descriptions mix up the backing or imply both use the same approach.