Brick, a common building material, is highly resistant to fire. Its composition and manufacturing process give it high resistance to high temperatures. This resistance stems from processes that occur long before a brick is ever laid in a wall.
The Science of Brick and Fire
Bricks are primarily composed of natural materials such as clay and shale, sometimes mixed with sand or other stabilizers. These raw materials are shaped and then subjected to an intense firing process in kilns. During manufacturing, bricks are fired at extremely high temperatures, typically ranging from 800°C to 1200°C (approximately 1,472°F to 2,192°F).
This high-temperature treatment removes water content and organic materials from the clay, fundamentally altering its molecular structure. The process results in a dense, ceramic-like material that is chemically inert and non-combustible. Unlike wood, which readily burns due to its carbon-rich composition, bricks do not ignite, feed a flame, or produce significant smoke or toxic gases when exposed to fire.
What Happens to Brick in Extreme Heat
While brick does not combust, prolonged exposure to extreme heat can still affect its physical properties. Spalling occurs when trapped moisture turns to steam, causing the surface to flake or chip. This can also happen if the brick’s surface heats significantly faster than its interior.
Cracking results from thermal expansion and contraction. Structural components, including bricks and mortar, expand at varying rates when heated, creating internal stresses. Rapid temperature changes, such as when hot bricks are suddenly cooled by water during firefighting efforts, can also induce thermal shock and lead to cracking. Discoloration may also occur due to intense heat or soot deposition.
Although bricks themselves maintain their integrity well, mortar joints can be more susceptible to heat damage. Cement mortar, for instance, can begin to disintegrate at temperatures around 450°C (842°F). This weakening of the mortar can compromise the overall structural integrity of a brick wall, even if the bricks remain intact.
Brick as a Fire-Resistant Material
Brick’s properties make it an effective fire-resistant construction material. It acts as a robust barrier against fire and smoke. Its low thermal conductivity slows heat transfer through walls, helping contain fires and prevent spread.
In a building fire, brickwork helps maintain structural integrity for extended periods. Unlike materials that deform or melt rapidly when heated, brick remains stable, providing valuable evacuation time. This capability makes brick common in fireplaces, chimneys, and as a general building material to enhance fire safety, often protecting structures from exterior fires for an hour or more.