What could happen if masonry is exposed to too much heat?

• A. The mortar between bricks, blocks, and stone may degrade and show signs of weakening
• B. Masonry becomes waterproof
• C. Concrete blocks will always spall completely
• D. The whole wall becomes stronger

Answer: (A)

Excessive heat damages the mortar that binds masonry units together. When masonry is heated, the cementitious mortar loses strength and its bond to bricks, blocks, or stone can deteriorate, especially if moisture is present. Heat can also drive out moisture and cause internal pressure, leading to cracks and weakened joints. As the mortar deteriorates, the overall integrity of the wall diminishes, reducing its ability to carry loads and resist further fire exposure.

Heat does not magically make masonry waterproof; cracking and spalling can actually increase water intrusion. Spalling of blocks is not guaranteed to occur in every situation, and a wall does not become stronger from heat—the opposite is true, as high temperatures weaken the structure.