How many coats are required when installing gypsum over metal lath or wire mesh?

When installing gypsum over metal lath or wire mesh, the requirement is typically for three coats. This procedure consists of a scratch coat, a brown coat, and a finish coat.

The scratch coat is the first layer applied directly to the metal lath or wire mesh, allowing for good adhesion. After the scratch coat has set, the brown coat is applied, which serves to build up the thickness and provide a level base for the final finish. The finish coat is the last layer, providing a smooth surface that is suitable for painting or other finishes.

This three-coat system not only enhances the durability of the installation but also ensures that the finished surface has the desired appearance and integrity. Each coat serves a distinct purpose in creating a stable and reliable gypsum surface over metal lath or wire mesh.