Which tool is primarily used for creating horizontal lines during masonry layout?

The tool primarily used for creating horizontal lines during masonry layout is the chalk line. A chalk line consists of a string coated with chalk powder, which is used to snap a straight line across a surface. It is essential for achieving accuracy in layout work, particularly when marking guidelines for bricks or blocks to ensure they are installed in a straight line.

Using a chalk line allows masons to establish a clear reference point over long distances, which is critical for maintaining consistent alignment and levels throughout the masonry project. This tool enables efficient and precise work, which is vital in masonry to ensure structural integrity and aesthetic alignment of the finished product.

While other tools have specific applications — such as a bevel square for checking angles, a trowel for applying mortar, and a level for checking vertical and horizontal lines — none of these serve the primary function of creating a horizontal reference line as effectively as a chalk line does in the layout process.