It’s perfectly normal for every kiln to to develop heat generated cracks over time and use. We all know that firebrick cracks, but so can ceramic fiber. As each material heats and cools, it will expand and contract with each firing. This will inevitably cause those pesky cracks. Most cracks in your fiber are minor and mostly cosmetic, but they can also occur on a firing surface on an all fiber kiln. Since the fiber is such a good insulator, those cracks you see on the surface hardly allow any heat to be lost. That is... unless you have a gaping hole to the outside.
If you’re not sure what kind of material your kiln is made from, here’s the lowdown on how can you tell a ceramic fiber kiln from a firebrick kiln from Arnold Howard, Engineer at Paragon, "Ceramic fiber is white, light-weight, and has a fairly smooth surface. Firebricks are porous. A firebrick firing chamber has seam lines where the firebricks are cemented together."
Arnold’s easy to follow instructions for filling damaged areas of ceramic fiber are listed below... so, go get yourself a caulking gun and let’s get to it!
HOW TO REPAIR A CERAMIC FIBER KILN WITH PYROLITE
1) Unplug the kiln. Scrape/sand the ceramic fiber to remove glass, ceramic glaze, or other melted contaminants. Remove as little fiber as possible. If a heating element is located where you are scraping, avoid touching the element.
2) Vacuum the dust from the damaged area. Remove all the contaminant. Otherwise it will melt and embed deeper into the firing chamber. Keep the vacuum cleaner nozzle at least 2” from the thermocouple and the controller. This is to avoid damaging the controller with static electricity, which can build up on the nozzle.
3) Squeeze the Pyrolite into the gouge. Pyrolite is similar in consistency to window caulking. Smooth the Pyrolite with a small putty knife or credit card and smooth it evenly. Allow it to dry before firing the kiln. You can send to level and smooth after the Pyrolite is fired.
I hope this little cosmetic tip helps you spruce up, and makes you and your kiln feel young again!