Fire bricks are heat resistant bricks used to line the interior of fireplaces, kilns and stoves. They insulate and reflect the heat back into the fire, maintaining a high temperature and preventing damage to the wall behind a fireplace. A cracked fire brick can allow heat to escape and should be repaired. Due to the high temperatures that fire bricks are exposed to, fire cement should be used. Repairing fire bricks is a quick, easy and cheap job.
Clean any soot, grease or dust from the fire brick that is to be repaired. Allow the brick to dry before beginning the repair.
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, again removing any excess.
Apply heat to the fire brick, gradually increasing the temperature over a three- to four-hour period.
Allow the brick to cool, and check for any further cracks. If cracks are found, repeat steps 1 through 3.