Masonry Firebox Repair

Is a masonry firebox repair necessary?

A new fireboxHere’s what a brand new masonry firebox looks like.

With usage, cracks and gaps in the firebox bricks and mortar, especially at the back wall, are a potential fire hazard and therefore a masonry firebox repair should be done.

The area behind the masonry firebox sidewalls are typically hollow.

Since a fire will produce a minimum of 500 degrees of heat, cracks and gaps in the bricks and mortar will expand and transfer that heat and gases to combustible building materials of the house such as wooden walls studs or drywall.


The solution

In most cases, it is possible to widen the cracks and then fill in with a high temperature mortar patching material.

After the patching, we recommend installing a stainless steel Heat Shield for added protection since it will reduce the heat to the back wall.

Without a masonry firebox repair, the cracks will increase in length and depth and eventually the damage will be beyond patching. In that case, we would refer you to a qualified chimney mason for a more extensive repair or even to have the firebox rebuilt.


  • A firebox in need of a masonry firebox repairCracks in Firebox
  • A firebox after a masonry firebox repairAfter Masonry Firebox Repair
  • A heat shield in front of a masonry firebox repairWith Black Stainless Heat Shield

Please Note

A masonry firebox repair is not the same as rebuilding the firebox.

While we do our best to make as clean a repair as possible, you will see where it has been patched. Also, over time it is likely that the area will need to be patched again, especially if the damage to the back wall was extensive.

The heat shield goes a long way toward protecting the patching.  A heat shield reduces the heat to the back wall, will maintain the patch and will extend the life of the back wall.

In addition, we recommend painting the firebox black after the firebox repair, for a cleaner look and to cover the patch.