What is the function of an S-shaped jointer?

The role of an S-shaped jointer is specifically to tool vertical joints in masonry work. The design of the S-shaped joint allows for the creation of a smooth, well-defined finish on vertical mortar joints between masonry units. This finish not only adds to the aesthetic quality of the masonry but also helps in the proper water drainage from the joint.

When vertical joints are tooled with an S-shaped jointer, they tend to have a slightly rounded edge that can help prevent water from being trapped in the joint, which is crucial for maintaining the integrity of the masonry over time. Additionally, this type of jointer allows the mason to effectively compress the mortar within the joint, providing strength and durability.

The other choices involve tasks that do not align with the primary purpose of an S-shaped jointer, which is explicitly designed for vertical applications. Tools that check height, tool horizontal joints, or split masonry units serve distinct functions that do not pertain to the specific action of toiling vertical joints.