Scratch Coat

Definition

A scratch coat is the first coat in a three-coat application of plaster.

Purpose

The purpose of a scratch coat is to provide a rough, textured base layer that adheres well to the substrate and allows subsequent plaster coats to bond effectively.

Examples of Use

• In traditional plastering, the scratch coat is applied to lath or masonry surfaces as the initial layer.
• Stucco applications use a scratch coat to create a strong foundation for the finish coats.
• Scratch coats are used in tile installations to prepare walls for a smooth, even surface.

Related Terms

• Brown Coat: The second coat in a three-coat plaster system, applied over the scratch coat.
• Finish Coat: The final coat of plaster that creates a smooth, decorative surface.
• Lath: A base layer of wood or metal strips used to support plaster.

Notes

The scratch coat must be properly mixed and applied to ensure good adhesion and a solid foundation for the following plaster layers.