Final answer:
A wall scratcher is used in construction to score the surface of walls to improve the adhesion of plaster or stucco layers.
Step-by-step explanation:
The main purpose of using a wall scratcher is to score the surface of walls for plastering. This tool creates grooves in the wall's base layer, known as scratch coat, to ensure that subsequent layers of plaster or stucco have something to grip onto, improving the adhesion between the layers. Using a wall scratcher is crucial in construction and renovation projects, especially when preparing walls for plastering to prevent future issues such as cracking or delamination of the plaster.