Bricks are inherently non-combustible ceramic materials composed mainly of clay or shale. These materials, mixtures of silica and alumina, do not ignite or burn when exposed to fire. This property makes them a highly valued component in construction for fire safety. A standard brick cannot catch fire because its manufacturing process essentially pre-burns the material.
The Composition That Prevents Burning
A common brick is made from naturally occurring, oxidized mineral compounds, primarily silica and alumina. These raw materials are formed into blocks and then subjected to intense heat treatment known as kilning. During this firing process, which typically reaches temperatures between 1,800°F (982°C) and 2,400°F (1,316°C), all organic matter and moisture within the clay are completely removed.
This high-temperature exposure transforms the clay into a durable ceramic body. The heat causes a process called vitrification, where silica components melt and fuse together, creating a dense, stable material. Since the material has already endured temperatures far exceeding those of a typical house fire, there is no remaining combustible content to fuel a flame. Bricks do not contribute to the start or spread of fire.
Brick Performance Under Intense Heat
While a brick will not burn, it does react to the prolonged and extreme heat of a major fire. Bricks possess a high thermal mass, meaning they absorb and store heat energy slowly, which delays the transfer of heat to the other side of a wall. This property allows brick walls to provide a significant fire resistance rating, often delaying structural failure for hours.
The most common form of damage to a brick under fire conditions is known as spalling. Spalling occurs when the brick surface breaks away or chips off, often due to rapid temperature changes or the expansion of trapped moisture. Intense heat causes the surface layer to heat much faster than the interior, creating internal stress that leads to flaking.
Spalling can also be exacerbated by water from fire hoses hitting the superheated brick, causing a sudden, violent contraction that cracks the material. Prolonged exposure to extreme heat can eventually lead to a loss of structural integrity and softening of the mortar joints. Mortar tends to weaken faster under high heat than the brick, affecting the overall stability of the wall assembly.
Fire Risk in Brick Buildings
The presence of brick does not automatically render a building fireproof, as the overall safety profile depends on the entire construction system. A brick building consists of many other highly combustible materials, such as wood framing, floor joists, and roof trusses. Fire spreads quickly through these non-brick components.
Interior finishes like drywall, insulation, and the contents of the building are all fuel sources for a fire. The brick exterior often functions as a robust fire barrier that contains the fire within a compartment or protects the interior structure from an external blaze.
Because a brick wall slows the rate of heat transfer, it provides occupants with valuable time for evacuation and for fire services to arrive. If the fire penetrates the interior structure, the non-brick elements can burn and collapse, even if the exterior masonry shell remains standing. The fire rating of a wall is a function of the entire assembly—including the brick, the mortar, and internal wall components—not just the brick material alone.