cast iron sewer pipe repair - man digging trench for sewer line

How to Make an Underground Cast-Iron Sewer Pipe Repair (in 7 Steps!)

Soil can crush or roots can grow into a cracked main sewer line, causing the entire plumbing system to back up. Even without a blockage, a soggy, smelly lawn may indicate a leaking underground pipe.

Excavating your yard to locate and repair a sewer line — and landscaping the damage afterward — is a major job. But you can save money repairing a cast iron sewer pipe yourself. If money is a big factor, then this article is for you.

I’ll take you through the 7 basic steps for repairing a cast iron sewer pipe. In fact, these instructions will work for repairing a plastic sewer pipe too.

Tools & Materials

To get started, you’ll need the following list of tools and materials. But keep in mind, before you make any purchases or rentals, the labor involved in excavating and repairing a sewer line pipe is heavy. Don’t attempt this unless you’re in good physical health.

  • Hammer and mallet
  • Saw (to cut wood)
  • Thick gloves
  • Safety goggles
  • Plywood sheets (as many as needed)
  • Shovel
  • Ratchet cutter (to cut cast iron pipe) or short-handled saw (to cut plastic pipe)
  • 2×4″ wood (to brace trench walls)
  • Stainless steel pipe clamps (fitted to the pipe)
  • Neoprene sleeve
  • Screwdriver
  • Socket wrench or nut driver

1. Mark the Sewer Line

Begin by tracing the path of the sewer line from the main drain to the sewer or septic tank. Ask your local authorities for permission to work on the sewer pipe, and for information about its location and depth.

Next, stake out the path of the sewer line and hire a contractor with a backhoe to dig a trench within 1 foot of the pipe. You can rent and dig the trench yourself, but we strongly recommend you hire an expert for this phase of the project. If you damage the pipe yourself (and it’s easy to do), you’ll be liable. Best to put that liability on someone else.

cast iron sewer pipe repair - 1 mark the sewer line
Step 1 of a cast iron sewer pipe repair: mark the sewer line.

2. Reinforce the Trench

If the soil is loose or sandy, make the trench safe to work in by shoring its walls. Clay soil generally does not require shoring. Gravel soil requires shoring at the bottom only.

Lower sheets of 3/8-9inch exterior-grade plywood into the trench to line the walls. If the soil is especially loose, brace the trench for extra support (see next step).

cast iron sewer pipe repair - 2 reinforce the trench
Step 2 of a cast iron sewer pipe repair: reinforce the trench.

3. Brace the Trench Walls

Cut enough 2x4s, slightly longer than the width of the trench, to brace the walls every three or four feet. Mail each of the supports to the plywood sheets between waist and shoulder height. Leave enough space between braces to dig with a shovel.

cast iron sewer pipe repair - 3 brace the trench walls
Step 3 of a cast iron sewer pipe repair: brace the trench walls.

4. Expose the Main Line (Sewer Line)

Because you likely won’t have access to (or the expertise to operate) a sewer line inspection camera, you will have to find the damaged pipe manually.

To locate the leak, look for an area of wet soil in the base of the trench. Now turn off the main water supply and be sure that nobody uses any fixtures during the repair.

Dig around the broken section of the pipe so that it is completely exposed. When the sewer pipe is plastic, use a plastic replacement pipe. If it is cast iron, replace it with plastic if your local plumbing code permits (it probably will). If not, go ahead and replace it with cast iron. Both are attached with hubless (neoprene sleeves held in place by stainless steel clamps).

Caution: Plumbing supply lines or electrical cables may run parallel to the sewer line. Work with extreme patience and gently text the ground before you dig.

cast iron sewer pipe repair - 4 expose the sewer line
Step 4 of a cast iron sewer pipe repair: expose the sewer line.

5. Prepare to Cut the Cast Iron Pipe

We’re at about the halfway mark in making the cast iron sewer pipe repair. Good job.

Now, with a piece of chalk, mark the section of pipe to be replaced. Make sure all of the damaged pipe is within the chalk lines before you begin cutting.

If you have a plastic sewer pipe, you can cut it with a short-handled saw. If you have a cast-iron pipe, you’ll need to rent a ratchet cutter from a local rental center. For the cast iron pipe, wrap the cutting chain around the chalk line and secure it to the handle. Set the dial to CUT and turn the adjusting knob clockwise to tighten the chain around the pipe.

cast iron sewer pipe repair - 4 expose the sewer line
Step 5 of a cast iron sewer pipe repair: prepare to cut the cast iron pipe.

6. Cut the Cast Iron Pipe

Wearing your safety goggles, pump the handle of the ratchet back and forth to cut through the pipe. Loosen the adjusting knob, unlock the chain, slide the ratchet cutter to the other chalk mark and repeat the process.

Remove the damaged pipe and push loosely wadded paper towels (or old rags) into the remaining pipe ends to block any harmful sewer gas.

cast iron sewer pipe repair - 6 cut the cast iron pipe
Step 6 of a cast iron sewer pipe repair: cut the cast iron pipe.

7. Cut & Fit the New Pipe

Finally, we’ve made it to the last step in your cast iron sewer pipe repair. You’re almost done.

Cut the replacement pipe, whether cast iron or plastic, about 1/4-inch shorter than the old piece that you removed. Slide a loosened clamp onto each standing pipe. Force both ends of the replacement pipe halfway into the neoprene sleeves, then fold the lips of the sleeves back over the pipe.

Fit the section between the standing pipes and fold the sleeves in place with the help of a screwdriver. Position a clamp over each joint, then tighten the clamp screw securely with a socket wrench or nut driver.

Have the repair examined, if required, by someone in charge of the local plumbing codes. Pack the earth you removed earlier around the pipe so it slopes away from the house. Remove the plywood and supports.

PRO TIP: Wait a day or two to be sure there are no leaks before filling in the trench.

cast iron sewer pipe repair - 7 cut and fit the new pipe
Step 7 of a cast iron sewer pipe repair: cut and fit the new pipe.

Final Thoughts: Cast Iron Sewer Pipe Repair

As you can see, excavation and repair of a cast iron sewer pipe are difficult and time-consuming. However, with diligence, patience, and the right tools, you can do this with just a little bit of assistance (like a professional excavator and a friend or two).

If you determine that this job isn’t for you, get a few different estimates. Just make sure they come from plumbers with drain technicians and excavation experts on hand.

Call 1-Tom-Plumber

Don’t hesitate to contact us here or call us at 1-Tom-Plumber (1-866-758-6237) if you need help with any kind of sewer line repair or replacement, whether cast iron or plastic.

1-Tom-Plumber’s certified team of plumbers and drain technicians respond immediately to any emergency plumbing, drain cleaning, or water damage problem. We also handle the excavation of underground water lines and sewer main lines. Our immediate-response team is available every day and night of the year, even on holidays.

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