What is the minimum number of coats required for gypsum plaster applied over metal lath?

Gypsum plaster applied over metal lath typically requires a minimum of three coats to achieve proper adhesion, thickness, and finish quality. The first coat, known as the scratch coat, is applied to form a key for the subsequent layers. It is followed by a second coat, commonly referred to as the brown coat, which builds up the thickness and further embeds the lath. Finally, the third coat, known as the finish coat, provides a smooth surface that is ready for decoration or painting. Each coat serves a distinct purpose and contributes to the overall durability and performance of the plastering system.

While it may seem feasible to achieve a satisfactory finish with fewer coats, the three-coat system is the industry standard due to the structural integrity it provides and the quality of finish achievable. This requirement also accounts for potential settling or movement within the underlying structure, ensuring that the plaster remains intact and aesthetically pleasing over time.