How to Repair a Cast Iron Pipe

Learn how to repair small crumbles or leaks in an old cast iron pipe with our expert-backed advice.

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Old cast iron drainpipes can behave unpredictably. Sometimes a small section of a pipe starts to crumble or a joint begins to leak even though most of the pipe is sound. If this is the case in your home, you can—in most cases—easily make the repair yourself. However, if a cast iron pipe fails at several points, the most economical solution is to replace it with PVC pipe, which is a job for a professional.

Cast iron pipes are very heavy and must be held in place with special clamps and framing members. When doing repair work on a cast iron pipe, it's important not to disturb these clamps—if one weakens, a long section of pipe could come crashing down. In addition, some older cast iron joints were sealed with molten lead, but this does not pose a danger to your health because only wastewater passes through the pipes. If you need to patch a joint on a cast iron pipe, expect to spend an hour or more doing so. If you're just patching a hole, it may take even less time.

What You Need

  • Wire brush
  • Hammer
  • Cold chisel
  • Putty knife
  • Repair paste or plumber's epoxy
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Step 1: Clean Away Corrosion

If you spot water or a bad smell coming from an old leaded joint, use a cold chisel and hammer to gently tap the lead back into the joint. Use a wire brush and rag to clean away any corrosion.

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Step 2: Fill with Repair Paste

Fill the resulting void with cast iron pipe repair paste, using a putty knife to apply the paste evenly.

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Step 3: Fill Any Holes

If a pipe rusts through or is punctured, clean the opening with a wire brush and fill the hole with a two-part plumber's epoxy. Check the manufacturer's instructions for drying time, and make sure the pipe isn't in use until the patch has been completely set.

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