Along with any part of your home, your fireplace requires maintenance to ensure your family’s safety during its use.  There are three main components to your fireplace; the firebox itself (Modular, Masonry or Metal), the damper / chimney system and the fire brick liner. Fire bricks absorb heat, providing a buffer between the fire and the firebox, maintaining a high temperature and preventing damage to the wall behind a fireplace.  Fire brick mortar and/or fire bricks can become damaged after years of use which can cause a fire brick to fall out or crack.  A cracked or damaged fire brick can be a potential fire hazard and should be repaired or replaced before using the fireplace again.

Repairing Cracked Fire Brick

Supplies Needed:
Fire Cement

Directions (for Individually applied Fire Brick):

1. Clean any soot, grease or dust from the fire brick that is to be repaired – allow brick to dry before beginning the repair.

2. Apply fire cement to the area that is being repaired, using the trowel.  If the brick has broken into more than one piece, apply a layer of cement along one edge of the break and push the pieces firmly back together.  Wipe any excess cement from the brick.  If repairing a crack, work the cement well into the area, removing any excess.

3. Apply heat to the fire brick, gradually increasing the temperature over a three to four hour period.

4. Allow the brick to cool and check for further cracks.  If additional cracks are found, repeat steps 1-3.

Replacing Damaged Fire brick

Supplies Needed:

Carbide-Tipped Scoring Tool meant for cutting tile backer board
Metal Jointer
Brick Trowel
Tuck-Pointing Trowel (narrow enough to fit in the brick joints)
Dry-Mix Refractory Mortar

Directions (for Individually applied Fire Brick):

1. Scrape out the loose mortar.  Rake out the joint with the scoring tool – start gently, probing for areas that are loose.  Dig out the deteriorated mortar until the joint is about ½ to ¾ inches deep and the brick surface on both sides of the joint are mortar free.

2. Brush the joint.  Use an old paintbrush and vacuum to sweep the joints clean.  Brush water onto the joints and brick faces (mortar doesn’t stick to bone-dry brick well).

3. Pack the mortar.  Mix a small batch of mortar according the mortar directions and apply to the brick in line with the joint – pack into the joint with a tuck-pointing trowel.  Pack about halfway full, then press firmly as you pull the pointing trowel (handle first) along the joint until joint is filled.

4. Clean up by scraping the excess mortar off of the brick faces and then wipe immediately with a damp sponge.
Let the mortar dry completely for several days – after completely dry, rough up with a metal chisel if desired so it matches the surrounding mortar.

5. For factory built fireplaces with installed fire brick panels, contact the Fireplace Manufacturer for instructions on replacement/repair.

NOTE: Though each individual mason may have their own technique because of geographic conditions or training, these are some general procedures for repairing cracked fire brick.

Sources:, This Old House