How to Repair a Cast Iron Pipe

Learn how to patch cracks, breaks, and pinhole leaks in a cast iron pipe with our expert-backed advice.

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Photo: Jay Wilde
Project Overview
  • Total Time: 2 hours
  • Skill Level: Advanced

Over the past 100 years, cast iron pipes have been used in plumbing construction to bring water into homes and remove waste and wastewater. However, cast iron pipes typically only last about 50 to 100 years, so there are many older homes that are now dealing with cracks, leaks, and pipe collapses, leading to serious water damage, time-consuming clean-ups, and costly renovations.

If you have cast iron pipes in your home, it’s a good idea to inspect the pipes about once a month for signs of rust, corrosion, or leaks. Cast iron pipes typically fail due to corrosion from the inside, so without proper inspection, the pipe may collapse, seemingly without warning. In reality, the inside of the pipe can be gradually worn down to the point that certain areas are almost paper thin. 

Pinhole leaks, cracks, and even some larger holes in cast iron can be patched using epoxy or a combination of epoxy and waterproof repair tape, depending on the severity of the damage. Use this guide to learn how to repair a cast iron pipe and determine when it’s time to call in a professional plumber.

Signs of Leaking or Damaged Cast Iron Pipes

Pipes are typically kept out of sight behind walls, under floors, and in ceilings, so it’s not always easy to see problem areas. Once a month, it’s recommended to inspect any exposed parts of a cast iron pipe for any signs of damage. Common signs include leaks, sewer odors, backups, mold growth, isolated areas of lush lawn growth, and cracks in the foundation.

  • Leaks in any exposed parts of the cast iron pipe are relatively easy to spot, but if the damaged area of the pipe is in the wall or floor, you may see signs of damaged drywall or water-damaged floor before realizing the cause is an active leak.
  • Sewer odor can indicate that there is a problem with the drain lines for the home. Check the cast iron pipe in the vicinity where you smelled the odor to track down the damaged area of the pipe before the problem can get worse.
  • Backups, like slow-draining sinks, clogged shower drains, and toilet backups can be a sign your pipes are failing.
  • Mold growth often occurs in damp, dark locations. Given that cast iron pipes tend to be installed in walls, ceilings, floors, and basements, it only makes sense that mold would start to grow in these dark areas if there are leaking or damaged drain lines.
  • Isolated areas of lush lawn growth can act as an indicator of leaking or damaged cast iron pipes. If there is a crack or break in the line running under the lawn, the wastewater from the cast iron pipe can increase the nutrients in the soil, leading to small patches of excessive lawn growth.
  • Cracks in the foundation of the home are a serious indicator that there may be a problem with the plumbing. Leaking pipes can gradually eat away at the soil around the home and foundation walls, leading to structural problems with the walls, floors, and ceilings.

What You'll Need

Equipment / Tools

  • Wire brush
  • Putty knife


  • Paper towels
  • Grit cloth
  • Rag
  • Epoxy for cast iron repair
  • Waterproof repair tape


Repairing a cast iron pipe isn’t a significantly dangerous job, but it’s still a good idea to keep your hands and lungs protected by wearing a mask and a pair of work gloves. Consider using closed-toe shoes, long pants, and a long-sleeve shirt to keep your arms, legs, and feet properly protected while you work.

  1. Locate the damaged area.

    First, figure out where the pipe is damaged. If the damaged location is buried in the wall, ceiling, floor, or under the yard, you may need to call in a professional plumber to avoid doing unnecessary damage to the home.

    However, you can handle minor repairs without calling in a plumber if you find that the cracked or leaking spot is located on an exposed section of the pipe. A good method of finding a minor leak is to wipe down the pipe, then wrap a paper towel around the suspected location. Any wet spots on the paper towel will show up immediately, indicating the exact spot where the pipe is leaking. 

  2. Prepare the cast iron pipe.

    If the cast iron pipe is a water line, turn off the water to the home and open the nearest faucet to drain the water. If the problem pipe is a wastewater line, you'll need to make sure no one uses a sink or flushes a toilet until the repair is complete. Once you've found the damaged area on the cast iron pipe, use a combination of grit cloth and a wire brush to remove any surface rust and clean the cast iron material. Follow up with a rag or cloth to wipe away any leftover debris, so that the epoxy can adhere directly to the pipe without obstruction. 

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    Better Homes & Gardens

    Spread epoxy over damaged area.

    Read and follow the instructions provided by the epoxy manufacturer to prepare the product for use. Some products need to be kneaded before use, while others can be adhered directly to the pipe.

    When the epoxy is ready, completely spread it over the damaged area using a putty knife. Make sure the epoxy patch isn’t too thin or it may leak. Keep in mind that epoxy will dry and harden within about five to 10 minutes, so you can’t take too much time to apply and spread the epoxy.

  4. Apply waterproof tape to large holes.

    If the hole in the cast iron pipe is too big for a simple epoxy patch, you'll need to invest in waterproof pipe repair tape or liner specifically made for this purpose. Apply epoxy over the damaged area, then wrap the layer of pipe repair tape over the epoxy. This will help create a strong seal on the outside of the pipe. 

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    Better Homes & Gardens

    Let the epoxy dry and set.

    Epoxy putty will typically dry and harden within about five to 10 minutes, but it can take up to an hour to properly set. Similarly, it’s a good idea to clamp, hold, or otherwise secure the waterproof tape in position for about an hour to ensure that it bonds and sets properly before running water through the pipes.

  6. Check for leaks.

    After the repair is complete, check the leak by turning on the faucet at the nearest sink. Once the water is running, inspect the damaged areas for any signs of leaks. If you want further confirmation, consider wrapping the pipe with paper towel to check if any water is coming through the new patch.

When to Call a Professional

Cast iron pipes are not always easy to access. In many cases, the damaged areas may be buried inside a wall, ceiling, floor, or even under the ground. While you can spend time cutting open holes in the drywall, opening up the ceiling and floors, and digging in the yard to try to track down the damaged cast iron pipe, it's likely better to call in a professional plumber to find and repair the problem.

Professional plumbers have access to a wide range of tools and devices, as well as years of experience and hands-on training. This combination of skill and the appropriate equipment for the job allows them to locate the issue, diagnose the situation, and come up with a solution. Just keep in mind that if the damage seems like it is beyond a simple patch job, they will suggest the replacement of the pipe, which can be costly. Unfortunately, if the current pipe cannot be fixed, replacing it is the only option.

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