Mason's Line

The line gets reset and re-tensioned at every course, usually stretched from corner to corner with line blocks that hook over the brick already laid, or from line pins driven into the joint. A mason lays to the line rather than to eye, buttering each brick and setting its outer edge to just kiss the string. On a long retaining wall or a straight run of veneer, skipping this step is how a wall ends up with a visible wave or bow that shows under raking light even though each individual brick looks fine.

We reset the line every single course on chimneys and long wall runs rather than trusting a few widely spaced checks, because small drift compounds fast over twenty or thirty courses. That matters more here than in milder climates: a wall that's slightly out of plane collects water in low spots along the face, and that water is what feeds the freeze-thaw cycle that eventually spalls brick or cracks joints. A dead-straight wall laid to the line sheds water evenly and ages a lot more predictably.