The purpose of scratching the scratch coat is to:

The purpose of scratching the scratch coat is to:

• A. Improve adhesion by providing a keyed surface
• B. Remove surface moisture
• C. Apply color
• D. Create air voids

Answer: (A)

Scratching the scratch coat creates a keyed, rough surface. That roughness provides a mechanical grip for the next plaster layer, so as it sets it locks into the grooves and ridges rather than trying to bond to a smooth surface. This keying greatly increases adhesion and helps prevent delamination of the subsequent coat. It isn’t about removing moisture, adding color, or creating air voids—the finish and curing processes handle those. The key is the mechanical interlock the scratched surface offers for the next layer.

Scratching the scratch coat creates a keyed, rough surface. That roughness provides a mechanical grip for the next plaster layer, so as it sets it locks into the grooves and ridges rather than trying to bond to a smooth surface. This keying greatly increases adhesion and helps prevent delamination of the subsequent coat. It isn’t about removing moisture, adding color, or creating air voids—the finish and curing processes handle those. The key is the mechanical interlock the scratched surface offers for the next layer.