Which type of brick arrangement is considered the least stable?

The stack bond is considered the least stable type of brick arrangement due to its vertical alignment of bricks without overlapping. In a stack bond, each course of bricks is directly aligned with the ones above and below it. This configuration creates a continuous line without the interlocking strength seen in other bond patterns. The lack of staggered joints means that there is less resistance to horizontal forces, such as those caused by wind or seismic activity, making this bond arrangement more susceptible to failure under such stresses.

Other bond types, such as Flemish bond, English bond, and running bond, incorporate staggered bricks that enhance structural integrity by distributing load and resisting lateral forces more effectively. Their designs allow for greater stability, which is why they are preferred in masonry construction over the stack bond.