Clay fire pits are a decorative alternative to steel or stone fire pits. Unfortunately, over time, cracks can appear in the clay walls of a fire pit, most commonly due to moisture seeping into the clay and then expanding due to high temperatures. Hairline cracks are common and usually not a concern. Larger cracks, however, should be repaired before the fire pit is used further.
Carefully use a putty knife or pocket knife to remove any loose chunks of clay from the crack. If you are using a pocket knife, use one that you don't intend to keep sharp.
Sand the crack with coarse grain sandpaper to remove any remaining loose chunks of clay. Use a coarse grain sandpaper so that the edges of the crack are slightly scuffed, allowing the patch to adhere more effectively.
Purchase automotive bondo from an automotive supply store or castable refractory cement from a well-stocked hardware store. Whichever filler you choose to use, read the label to ensure that it will withstand high temperatures.
Mix the filler according to the manufacturer's instructions.
Apply the filler to the crack using a putty knife. Use the point of the knife to ensure that the filler fills the crack completely.
Use the flat edge of the putty knife to scrape away excess filler.
Allow the filler to dry completely. Drying can take anywhere from two days to two weeks depending on the depth of the crack and the weather. Cool, damp weather will require longer drying times than warm, sunny weather.
Sand the filler with coarse grain sandpaper until it is flush with the wall of the fire pit.
Paint the crack, or the entire fire pit, if desired. Use a primer and paint resistant to high temperatures. High temperature paint can be purchased at most well-stocked hardware stores.
Seal the fire pit with a high temperature sealant. You can purchase high temperature sealants at most well-stocked hardware stores. If you are unsure of which sealant to use, talk to a hardware store staff member and describe your project. The staff member will be able to direct you to the correct product.