Firebox Repair
The firebox takes the heat, so it is the part of a fireplace that cracks first. Some cracks are cosmetic. Others let heat through to the structure, and it takes a close look to tell which.
What the firebox is made of
A masonry fireplace has a firebox lined with firebrick set in thin mortar joints. Many factory-built fireplaces use manufactured panels instead. Both are meant to take the heat of a fire and shield what is behind them, but both wear out.
Common problems
| Problem | What it means |
|---|---|
| Hairline cracks in firebrick | Often cosmetic, but worth watching |
| Cracks wider than a hairline, or bricks that have shifted | Heat may be getting through to what is behind the firebox |
| Missing or crumbling mortar joints | The brick is no longer held in place or protected |
| Spalled or missing firebrick | The lining is thin or open in that spot |
| Cracked, warped or missing panels in a factory-built unit | They can often be replaced. See firebox panel replacement. |
| Heavy rust and flaking | Water is entering from above. See chimney leak repair. |
Repair options
- Repointing the firebox joints with a mortar made for fireplace use
- Replacing broken or missing firebrick
- Replacing panels in a factory-built firebox
- Resurfacing, in suitable cases
- A larger rebuild of the firebox lining if the damage is widespread
What is right depends on how bad the damage is and what is behind it. The wrong product, such as ordinary wall patch, will not survive the heat, so we only use materials meant for the purpose.
When to stop using the fireplace
If cracks are large, bricks are loose or you can see daylight, a hole or damage to the structure behind the firebox, stop using it until it has been inspected. For a fuller look at the fireplace, see fireplace inspection.
Cracks that look the same can mean very different things. The fix starts with understanding why the firebox cracked.
What the work involves
How a firebox repair goes
- InspectWe examine the firebox and what is behind it where we can.
- DiagnoseWe find out why it cracked or failed.
- RepairWe repair with materials made for fireplaces.
- CheckWe confirm the result and explain what to watch.
Questions
Frequently asked questions
Are cracks in firebrick normal?
Hairline cracks are common with age and heat. Wider cracks or movement need a closer look.
Can I patch it myself with a store-bought product?
Only products made for fireplace use can take the heat, and a patch over a bigger problem hides it.
Why does my firebox have white or rusty marks?
Often water. A cap or crown problem is a common cause.
Is a damaged firebox a fire hazard?
It can be if heat is reaching the structure behind it. That is why we recommend an inspection.
Ready to have your chimney looked at?
Call us, or send a scheduling request. We will contact you to confirm a time. Your appointment is not confirmed until we do.