What is the likely cause of a horizontal crack in the mortar of a 60-year-old brick masonry house?

• A. Excessive sand in the mortar mix
• B. Defective brick bonding
• C. Improper ceiling joist installation
• D. Differential settlement

Answer: (D)

A horizontal crack in the mortar of an exterior brick wall often signals movement of the wall itself, most commonly from differential settlement of the foundation. When different parts of the foundation settle unevenly, the wall experiences lateral and vertical stresses, which tend to open up joints in a relatively straight, horizontal line. Over many years, this pattern becomes evident as a long, continuous horizontal crack.

In a 60-year-old house, soil conditions, changing moisture, backfill, or nearby footing issues can contribute to uneven settlement, making this the most plausible cause.

Excess sand in mortar tends to weaken the mortar and cause cracking or spalling more randomly rather than producing a clean horizontal crack across a wall. Defective brick bonding affects how bricks join together but doesn’t typically create a persistent horizontal joint crack. Improper ceiling joist installation relates to roof/ceiling framing, not the masonry wall itself, so it wouldn’t be the primary cause of a horizontal mortar crack.