What indicates that a wall may be leaning and potentially unstable?

Unusual gaps between materials in a wall can indeed indicate that the wall may be leaning or at risk of instability. Such gaps often occur when structural elements shift or settle unevenly, leading to misalignments. When a wall leans, it can create spaces that are not consistent with the intended design, such as larger than normal openings between bricks, mortar, or between the wall and adjacent structures. These gaps can be a sign of underlying structural issues, such as inadequate support, soil movement, or deterioration of load-bearing elements.

In contrast, visible cracks in the foundation might indicate a different kind of problem, and while they are certainly concerning, they do not inherently mean that a wall is leaning. Even joints in bricks suggest a neat and consistent appearance rather than instability, which would require uneven spacing to indicate a problem. Walls appearing upright would not signify an issue either, as their vertical alignment is exactly what you would expect in stable structures. Therefore, the observation of unusual gaps serves as a clear and direct indicator of potential leaning and instability in the wall.