Cast iron sewer pipes, though long lasting and durable, are brittle and will crack if accidentally knocked. Though always best to repair cast iron cracks by replacing the broken pipe section, epoxy putty will seal the crack so the pipe is again usable. The putty comes in a tub in two separate colours, and it starts to cure (harden) when it comes into contact with air you begin to mix it to one uniform colour.
Wipe off all oil and dirt using a rag and solvent. Thoroughly brush the cracked area using a steel brush -- this helps to create an abrasive surface for the putty to bond to the pipe. Wipe off any small metal filings caused through brushing the pipe.
Cut the required amount of epoxy putty from its tube. Roll and knead the putty with your hands into one uniform colour -- wear rubber gloves if the putty irritates your hands. Apply the putty along the length of the crack on the cast iron pipe, making sure to cover the area around the crack to a width of 1/2 inch. Start applying the putty no more than one and half minutes after you finish kneading.
Wet your finger tips to smooth out the putty, thinning out the putty edges where it meets the cast iron pipe. Thoroughly wash your hands with hot water and soap after applying the putty to the pipe.
The putty will fully cure after one hour, with the cast iron pipe usable after this time. Epoxy putty operates in temperatures up to 149 degrees Celsius.