What is a common issue that can occur with bricks when exposed to heat?

When bricks are exposed to heat, especially during a fire or extreme temperature changes, a common issue that arises is spalling. Spalling occurs when the surface of the brick becomes damaged and starts to flake off or break away, which can happen due to the rapid expansion and contraction of the material caused by the heat. This phenomenon compromises the structural integrity of the brick and can lead to further damage over time as moisture seeps into the exposed areas.

The other options do not accurately reflect typical outcomes associated with heat exposure on bricks. While it is true that some bricks may sustain minor damage without showing outward signs, this is not a common issue tied specifically to heat. Total disintegration of bricks, although theoretically possible under extreme and prolonged heat, is far less common than spalling. Lastly, the idea that bricks become completely waterproof is misleading; exposure to heat typically leads to changes in their properties, but not waterproofing. In fact, once damaged, bricks can become more susceptible to moisture infiltration. Therefore, spalling is the most relevant and frequent consequence of heat exposure for bricks.