True or false: Heat exposure can cause masonry mortar to degrade and show signs of weakness.

• A. True
• B. False
• C. Not sure
• D. No effect

Answer: (A)

Heat exposure can degrade masonry mortar and weaken its bond. Mortar holds bricks or blocks together by binding them through hardened cementitious material, and its strength comes from hydration products that form during curing. When heated, moisture inside the mortar can turn to steam and create internal pressures, while dehydration of hydration products occurs as temperatures rise. This combination can lead to cracks, loss of cohesion, and reduced bond between the bricks and the mortar. Differential heating and cooling between the mortar and the masonry units also causes expansion and contraction at joints, promoting microcracking and eventual spalling or crumble of the mortar. In fires or prolonged high heat, these effects can become pronounced, making the wall weaker and more likely to fail or deteriorate. Signs you might observe include cracked or crumbling joints, loose bricks, and overall loss of joint integrity.