My firebrick has some cracks. What should I do?

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My firebrick has some cracks.  What should I do?

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  • The Knowledgebase is organized into a series of questions and answers having to do mostly with technical troubleshooting and understanding of kilns.
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My firebrick has some cracks. What should I do?

Firebrick cracks as it is heated and cooled- it is to be expected. When the kiln is hot, all the cracks fill in from the expanding brick. The biggest firebrick slabs are made with ceramic fiber expansion joints to accommodate this natural occurrence. Not every brick or slab cracks right away, but it seems that all bricks in the kiln, especially the slabs, will crack eventually.

  1. Keep the stainless steel bands around the slabs and the sections tight.
  2. Have a solid floor kiln stand like recent L&L stands, or add a 14ga galvanized steel or aluminum/ stainless steel plate between an older hollow-center stand and the slab.
  3. With bad cracks, fill with NON-RCF ceramic fiber- not too much- just full, not stuffed!
  4. Use a top shelf in the load to block falling brick chips and to secure a very cracked lid for a little while.
  5. Re-gluing slab pieces with high temp cement and water may work well for a while too, or they may crack again right away.

See this video:

Additional Actions to Take

  1. Dig out any loose particles with a small knife.
  2. Brush and vacuum the surface of the brick clean to remove any loose material or crumbling firebrick.
  3. Wet the brick surface lightly with clean fresh water. Use a paint brush or spray bottle (make sure there is no soap residue in the bottle).
  4. Apply a thin coat of brick cement all over the hole. This is defined as about 1/32" to 1/16" thick. Do this with your finger, a small brush, or a spatula.
  5. Fill hole with the special grout material. Apply grout with a spatula (like plaster). You can also use your finger. Push it into the hole. It is OK to let it be a rough surface or slightly larger than the hole it is filling.
  6. Let dry for 24 hours.
  7. Take some rough sandpaper and sand surface to even it out with the rest of the firebrick.
  8. Run the First Firing Cycle ( See first-firing.pdf in the Operation Section or see this search link).
  9. You can brush on brick facing afterward if you desire.
  1. Cut out an area around the brick chip with a small knife, saw or router. The hole that you make should have 90 degree angles so that a square or rectangular block will fit in the hole.
  2. Cut a piece of firebrick to fit into this cut out hole. The piece should be slightly smaller than the hole (by about 1/16" to 1/8").
  3. Both the hole and the brick piece should be brushed and vacuumed clean.
  4. Wet the surface lightly. (Both the hole and surface of the block that you are going to insert in the hole). Use a paint brush or spray bottle (make sure there is no soap residue in the bottle).
  5. Apply the Kiln Cement to the surface of the piece that you are going to put in the hole. Use only about 1/32" or 1/16" of cement.
  6. Insert cut piece of firebrick immediately and push into place so that it makes contact on all sides with the underlying firebrick.
  7. Let dry for 24 hours at minimum.
  8. Cut off and/or sand off excess brick and cement.
  9. Cover with Brick Facing and allow to dry for another 24 hours.
  10. Turn kiln onto low for 3 hours to dry totally.
  11. Run the First Firing Cycle (See first-firing.pdf in the Operation Section).

See this video: