Why are expansion joints required within long stucco or masonry runs?

• A. To reduce moisture intrusion.
• B. To accommodate thermal expansion and contraction and prevent cracking.
• C. To simplify maintenance.
• D. To increase load-bearing capacity.

Answer: (B)

When masonry or stucco runs are long, they are exposed to temperature changes that make materials expand and contract. If that movement is restricted, stresses build up and cracks appear along the wall. Expansion joints create deliberate gaps that are backed with flexible material, allowing each section to move independently. This movement absorption prevents cracking, delamination, and other damage that would occur from restrained movement. The joints are filled with a flexible sealant (often with a backer) to keep water out while still accommodating motion. They’re placed where movement is likely to be greatest—at intervals in long runs and at transitions in plane or height—so the system can accommodate thermal expansion and contraction safely. While joints can also help manage moisture and crack patterns, their primary purpose is to prevent cracking by allowing expansion and contraction. They do not increase load-bearing capacity.