Cast-iron is used mostly in older homes for the installation of sewer pipes. Though very durable and soundproof, it is brittle and can crack. Epoxy putty can be used to repair a crack. Available in a tube, the putty comes in two colours and starts to cure after it is kneaded and comes into contact with air.
Sand the cracked area thoroughly with 80-grit sandpaper to remove all signs of rust or dirt. If old epoxy putty exists around the crack, use a 4 1/2-inch angle grinder to remove the putty and smooth the area around the crack. Wipe the area using a damp rag to remove all dust, then use a dry rag to remove all moisture from the area.
Cut the desired amount of putty from the tube. Knead and roll it in your hands until the putty changes from two colours to one uniform colour.
Press the putty onto the cracked area of the cast iron pipe. Apply it within 1 1/2 minutes of kneading. Cover the pipe with the putty by one inch on all sides of the crack. Use damp fingers to smooth out the putty while it is curing. The putty will harden in eight minutes and fully cure after one hour.
If the epoxy putty makes irritates your skin, wash your hands and wear rubber gloves to apply the putty.