Which coat is applied first in a three-coat exterior plaster system?

Which coat is applied first in a three-coat exterior plaster system?

• A. Finish coat
• B. Brown coat
• C. Primer coat
• D. Base coat

Answer: (D)

The first coat in a three-coat exterior plaster system is the base coat. This coat forms the foundational layer that bonds to the substrate and establishes a flat, even surface with enough thickness to receive the remaining coats. It also provides a key or rough texture, which helps the next coats grip and stick properly. If you skip this early layer or apply the final finish coat directly onto the substrate, adhesion and a smooth, durable finish suffer. After the base coat sets, the next layer—the brown coat—adds additional thickness and strength and is worked to a uniform plane. The final layer, the finish coat, is then applied to provide the desired texture, color, and surface performance. The primer coat concept isn’t part of the standard three-coat sequence for exterior plaster; primers may be used in other contexts, but they aren’t a primary coat in this system.

The first coat in a three-coat exterior plaster system is the base coat. This coat forms the foundational layer that bonds to the substrate and establishes a flat, even surface with enough thickness to receive the remaining coats. It also provides a key or rough texture, which helps the next coats grip and stick properly. If you skip this early layer or apply the final finish coat directly onto the substrate, adhesion and a smooth, durable finish suffer.

After the base coat sets, the next layer—the brown coat—adds additional thickness and strength and is worked to a uniform plane. The final layer, the finish coat, is then applied to provide the desired texture, color, and surface performance.

The primer coat concept isn’t part of the standard three-coat sequence for exterior plaster; primers may be used in other contexts, but they aren’t a primary coat in this system.