Home Tap to Call Now

Why Is My Firebox Cracked?

Fireplaces are beautiful centerpieces in many homes. But, they require routine maintenance to keep them safe and efficient. Gas byproducts from burning wood take their toll on your fireplace and chimney system, but the firebox often suffers the most. Let’s look at what role the firebox plays in your chimney, what causes cracks, and what you can do about it.

Fireplace, firebox repair Marshfield, MA

What is the Firebox?

The firebox is the part of your fireplace where the fire burns, which means it’s the one component that’s exposed to the most heat. Typical fireboxes are made either from brick or stone, but sometimes metal. Modern fireboxes are constructed with materials designed to withstand the extreme heat produced by your fire, such as firebricks and refractory masonry. Factory-built fireboxes are mostly made from metal, but a refractory, heat-resistant material typically protects the firebox itself.

What Causes Firebox Cracking?

Regardless of the quality of the materials or the construction, all stone and brick fireboxes are prone to cracking, not necessarily from the heat but from other factors listed below.

  • Water
    Brick and stone are porous materials that absorb water like a sponge. If water gets into your chimney and down into the fireplace, it causes the material to swell and crack. Also, once water gets into the brick and mortar, it undergoes a freeze/thaw cycle, causing the water to expand, leading to cracks.
  • Wear & Tear
    Modern fireboxes are made from refractory mortar and firebricks designed to withstand the extreme temperatures produced by the fire. However, although these materials are fire-resistant, they will deteriorate over time due to the continuous heating and cooling cycle.
  • Lack of Maintenance
    Because the firebox must withstand heat and the sands of time, it’s important to hire a certified chimney service for annual inspection to reinforce or seal portions that show signs of wear. Routine maintenance is key to preventing long-term damage and ensuring your fireplace is safe.
  • Shoddy Construction
    While not as common, the materials used and the actual construction play a huge role in how long your fireplace lasts. We sometimes see fireplaces that were improperly built or were built with the wrong materials, causing them to deteriorate more quickly than they should.
  • Structural Movement
    A poorly constructed foundation or Mother Nature can cause your chimney to shift, putting stress on the entire structure, leading to chimney tilting and a damaged firebox.

The Importance of Immediate Firebox Repair

Although fireplaces are warm, inviting, romantic focal points of a home, they can be dangerous if not used properly or if you ignore damage. As strong as fireboxes are, time and use take their toll, resulting in damage. And, the damage differs based on the material used to construct the firebox. As mentioned, masonry fireboxes are prone to damage resulting from poor construction, water damage, and creosote acids that wear down the masonry.

We typically see the refractory panels wearing out with a factory-built firebox, leading to cracks, either in the panel itself or around the joints. Cracks and gaps in the firebox can allow toxic gases to enter your living room or allow heat to contact the combustible materials behind your fireplace and chimney, putting your family at risk of fire. Firebox deterioration, once started, will only get worse, which is why you must call a professional chimney repair service at the first sign of trouble to keep your fireplace safe and avoid expensive repairs down the road.

Firebox Repair vs. Replacement

Replacing a firebox is an expensive, time-consuming job, so it’s natural for homeowners to desire to go down the repair route before investing in a replacement. The severity of the damage and the age of the fireplace are the most significant factors when determining whether you can get by with repairs or if it’s time to replace it. If you have a masonry firebox, you have several repair options depending on the situation, including:

Tuckpointing & Joint Repair

For cracked or loose bricks and mortar, we may use a process called tuckpointing to fix the problem. Tuckpointing involves removing the damaged mortar and replacing it to restore strength and stability.

Firebox repair South Shore, MA


In cases where the damage is too extensive, or if your fireplace was constructed with inferior materials, we recommend completely rebuilding the firebox. A complete rebuild is the best option if your fireplace is no longer safe to use or when the cost of the repairs is close to the cost of rebuilding.

While your fireplace and firebox won’t last forever, you can extend their lifespan and make it more enjoyable to use by calling a certified chimney sweep service for annual maintenance and inspection. At Above & Beyond Chimney Service, we have over two decades of industry experience in fireplace and chimney repair, inspection, cleaning, maintenance, and rebuilding.

Our professional technicians are fully licensed and certified members of the National Chimney Sweep Guild. We strive to provide you with an experience that exceeds your expectations. If you live in South Framingham or the South Shore area, contact us today to book an appointment at 781-282-0415 or via our online form.