What observable issue may indicate deterioration of masonry units?

Spalling is a significant observable issue that can indicate the deterioration of masonry units. It occurs when sections of the masonry surface flake off or chip away, often as a result of moisture penetrating the masonry. This process can be exacerbated by freeze-thaw cycles, chemical exposure, or mechanical impacts. When spalling occurs, it reveals underlying damage and weakness within the masonry, which, if not addressed, can compromise the structural integrity of a building.

In contrast, while crumbling, color fading, and uneven surfaces can indicate some issues with masonry, they do not specifically point to the deterioration characteristic of spalling. Crumbling may suggest general breakdown but lacks the distinctive nature of surface damage that spalling represents. Color fading typically refers to aesthetic concerns rather than structural issues. Uneven surfaces can be a sign of settling or other structural problems but do not necessarily indicate the degradation of the masonry itself. Therefore, spalling stands out as a more direct indicator of masonry deterioration.