Removing the Firebrick
Before removing the firebrick, make note of the brick’s layout. Putting it back together can be like working a puzzle, so take a picture with your cell phone or digital camera before you begin working. Since you will be repairing cracked firebrick, this is a good time to replace any broken firebricks as well. Remove the firebricks, inspect them for cracks and set them aside for repair.
Repairing the Firebrick
Bricks that have cracks will accept wood stove cement. Some wood stove cements come premixed, while others require mixing. Use the cement appropriate to the application desired. Mixing it yourself will allow you to control the mixture, while using the premixed version lead to a thick and sticky application. Wet the area of the crack with a rag and apply the wood stove cement using a putty knife. Run over the application with a wet rag to smooth out the area. No sanding is necessary as this is going inside the stove.
Reinstalling Firebricks
Follow the picture you took to replace the firebrick in the wood stove. Make note that most stoves will have a metal lip under which the firebrick sits. The firebox sides often require a line of bricks stood up vertically on end and abutted one next to the other with the widest side facing the firebox. Some stoves may require the installation of the firebrick on the bottom first. Each stove’s firebox firebrick setup will vary according to stove manufacturer. Review your owner’s documents for specific installation of the firebrick.
Other Considerations
While replacing and repairing the firebrick, this is a good time to look at the fiberglass stove gasket as well, which might require replacing. If a firebrick is cracked or broken, this often means the stove has gone through a few winters. So review all areas of the stove that may need repair or maintenance. Don’t forget to run a chimney brush through the stovepipe, an easy rental from a tool yard or hardware store. Airtight wood stoves create more creosote in the pipe that requires annual cleaning.