How to Repair a Cast Iron Pipe Leak

Updated July 20, 2017

Cast iron pipes last for a long time, but this does not mean they cannot become damaged and start to leak. Leaks are usually caused by corroding sections, often around the leaded joints. A do-it-yourselfer can repair small leaks in joints and small holes, but a professional should handle large leaks. Cast iron pipes need proper care and maintenance in order to last.

Turn off the water supply to the pipe. Tap the joint lightly with a cold chisel and hammer. Cast iron pipe joints are soldered with lead; use a cold chisel to push the lead back into the joint.

Clean the repair area by removing rust with a wire brush and dusting away debris with a clean rag.

Fill the leaking area with a cast iron repair paste applied with a putty knife.

Let the area dry before letting water or waste re-enter the pipe.

Remove all rust and corrosion from the hole with a wire brush. Dust away debris with a clean rag.

Apply plumber's epoxy around the hole so the patch is flush with the existing area, using a putty knife. Follow the manufacturer's instructions on how to mix the epoxy.

Let the area dry before letting water or waste re-enter the pipe.


Do not disturb the pipe's supports. If the cast iron pipe supports are disturbed, the heavy pipe could fall down, injuring anyone in its way. Call a professional to repair sections of pipe or large repairs. Waste pipes contain toxic waste that can be hazardous to your health.

Things You'll Need

  • Cold chisel
  • Hammer
  • Wire brush
  • Clean rag
  • Cast iron repair paste
  • Putty knife
  • Two-part plumber's epoxy
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About the Author

Rachelle Proulx has been writing since 2000. She co-owns a pet-sitting company, providing her the experience to cover pet care and small business. Proulx is also a flooring specialist who writes about flooring options, preparation, application and maintenance.