Learn how to repair small crumbles or leaks in an old cast-iron pipe.


Old cast-iron drainpipe 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, you can easily make a repair. But if a cast-iron pipe is failing at several points, the most economical solution is to replace it with PVC pipe. This is a job for a professional.

When working with cast-iron, understand that the pipe is very heavy and must be held in place with special clamps attached to framing members. Never disturb these clamps; as if one weakens, a long section of pipe could come crashing down. Also, some older cast-iron joints were sealed with molten lead, but don't worry. This is not a danger to your health because only wastewater passes through the pipes.

If you need to patch a joint, expect to spend an hour doing so. If you're just patching a hole, it'll take even less time. Before you begin make sure the pipe is well-supported. 

What You Need

  • Wire brush
  • Hammer
  • Cold chisel
  • Putty knife
  • Repair paste or plumber's epoxy

Step 1: Clean Away Corrosion

If water or a bad smell comes 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 the corrosion.

Step 2: Fill with Repair Paste

Fill the resulting void with cast-iron pipe repair paste. Use a putty knife to apply the paste.

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 two-part plumber's epoxy. Check the manufacturer's instructions for drying time. Don't use the pipe until the patch has completely set.

Comments (1)

September 12, 2018
We repair cast iron pipes using the trenchless repair method. We use a picote drain cleaning machine to remove rust and loose debris. We then use a high pressure water jetted to clean the pipe. After the pipe is clean we use the patented perma-liner epoxy resin to create a new pipe . You now will have sewer lines that will have a 100 year life and a 50 year warranty. For more information see our website trenchless-repairs.com