What is the first coat called in a standard three coat plaster application?

In a standard three-coat plaster application, the first coat is referred to as the scratch coat. This initial layer serves several important functions. It is applied directly onto the lath (a framework of thin strips of wood or metal that provides support for the plaster) and is typically textured to create a suitable surface for the subsequent layers to adhere to. The scratching of the coat gives it a rough texture, which promotes bonding with the second layer, known as the brown coat.

The scratch coat is essential for establishing a solid foundation for the plastering system, allowing for better overall adhesion and reducing the likelihood of cracks as the plaster sets and cures. Understanding the role of each coat in plaster application is crucial for achieving a durable and aesthetically pleasing finish. Familiarity with the terminology and the function of the scratch coat is vital for anyone involved in plastering work.