What is the primary effect of expansion joints in preventing cracking in long masonry walls?

• A. They prevent moisture penetration.
• B. They allow differential movement and reduce crack propagation.
• C. They increase bond strength.
• D. They permanently seal joints.

Answer: (B)

Expansion joints are placed in long masonry walls to handle movement that comes from temperature changes, moisture variation, and foundation or structural shifts. When different parts of a wall expand or contract at different rates, stresses can build up and cause cracks. The joint creates a controlled gap that lets those sections move independently, so the stress is relieved within the joint rather than being forced to crack the masonry. By accommodating this differential movement, the joint helps keep cracks from starting or spreading across the wall. The flexible filler and sealant inside the joint accommodate and seal the movement, but the essential purpose is to allow that movement and limit crack propagation, not to permanently seal or to increase bond strength.