What is a major problem with masonry construction?

The five masonry challenges we see most often in existing buildings are brick demolition, mortar decay, sandstone erosion, algae growth, and efflorescence. Typical stone walls don't allow leaks, but modern concrete masonry units (CMU) are more porous. The materials used in its construction, and the design itself, make the CMU block very susceptible to leaks, which poses a risk to a foundation. This problem is also common if very old bricks were used in construction, as they are most likely unfired clay bricks.

Humidity is one of the most common causes of failure in masonry buildings. Water can easily seep into masonry walls exposed to the elements, and this could compromise their structural integrity. Water that enters a masonry wall and freezes and thaws will put pressure on everything the structure.