What is a fire-cracked brick?
A fire-cracked brick is one that cracked during firing, often internally as well as on the surface, and sounds cracked rather than clear when tapped. The cause is a fault in the firing cycle, typically cooling too fast or exposure to outside air at the wrong moment. There is no single settled English trade term; it is described as a fire-cracked or firing-cracked brick. Dutch has a specific word for it, ratelaar, which is where this entry originates.
How it differs from a hollow-sounding brick
The two faults are easily confused, but they are not the same defect.
| Fire-cracked brick | Hollow-sounding brick | |
|---|---|---|
| Defect | Cracks, including through the core | Internal voids |
| Cause | Rapid cooling, draught during firing | Uneven firing, core lags behind |
| Sound | Cracked, cut short | Dull, rattling |
| Visible | Cracks usually show on the face | Face can look perfectly sound |
Why they are sorted out
The brick is weakened along its cracks and takes up water through them.
- Keep them out of fair-faced brickwork. The cracks stay visible and tend to extend over time.
- Keep them away from frost. Water in a crack expands on freezing and opens the brick further.
- Keep them out of heavily loaded positions. Under a lintel, a trimmer joist or a column base, use a sound brick.
- Take care when cutting. A cracked brick breaks unpredictably along the existing fault line.
- Sort on delivery, not on the scaffold. Picking through bricks while laying costs time and produces worse work.
Spotting them on site
Hold the brick loose in one hand and tap it with a piece of steel or a second brick. A sound brick rings clear and short; a cracked one sounds split, as if the note breaks off early. Then look at the header faces: hairline cracks that carry on around a corner point to a crack running right through. For dry internal work that will be plastered and lightly loaded, such bricks often remain usable, provided they are stacked separately and used knowingly.
Checking bricks for firing cracks on site
- Sort on delivery: Not on the scaffold: picking through bricks while laying costs time and produces worse work.
- Tap the brick: Hold it loose in one hand and tap it with a piece of steel or a second brick.
- Listen to the note: A sound brick rings clear and short; a cracked one sounds split, as if the note breaks off early.
- Inspect the header faces: Hairline cracks that carry on around a corner point to a crack running right through.
Related terms
- Hollow-sounding brick
- Firing crack
- Drying crack
- Clinker brick
- Common brick
- Reject brick
Want to learn more about construction terms? Visit our knowledge base at fredsdiyplans.com.