What may occur if the lintel over doors and windows in a masonry wall rusts?

When the lintel over doors and windows in a masonry wall rusts, one of the primary concerns is the structural integrity of the masonry system itself. The lintel is a critical component that supports the weight of the wall above openings such as doors and windows. If the lintel rusts, it can weaken, causing it to lose its ability to support that weight effectively. This structural failure can lead to cracks at the tops of openings, as the masonry above begins to sag or shift due to the lack of support.

As the lintel deteriorates, it may no longer hold the wall above in place, resulting in the formation of cracks that often appear right at the tops of the door and window openings. This phenomenon is a clear indicator of structural distress and highlights the importance of maintaining lintels to avert potential and more severe issues.

While other options may touch on potential effects of lintel failures, the specific outcome of cracking at the tops of openings is directly correlated with the rusting of the lintel, making this choice the most accurate in this context.