I have a 2 inch cast iron pipe that is leaking at the cement line of a second floor condominium. The common line connects 3 stacked bathrooms.

My plan is to remove the concrete around the pipe that is leaking and if it is small and isolated using bondo to repair it, place an access panel where we cut the drywall in case we need to access that area again. Is using bondo to repair a 2 inch crack in cast iron a plausable repair?

If the crack is more extensive, my question relates to the best way to remove the 35 feet of cast iron piping. Should I open the ceiling in the garage; disconnect the plumbing on the first floor and slide the pipe through the open concrete; then cutting the concrete on the second floor disconnecting the second floor and sliding the pipe down to the garage and so on? Or as we slide the pipe down for second to first floor cut the pipe in small sections. And replacing the cast iron pipe, how would you proceed? Should I put a sleeve around the pipe that goes through the concrete? What material sleeve do you reccommend.

I can do the work with a friend, just need to know the logistics. Thank you.

2 Answers 2


Since this unit is one in a building of condos, an improvised DIY job is not acceptable; the job must be done right. I would assume that there is a collar that the pipe passes through, that is, the concrete is not adhering to the cast iron pipe. I would think that you must remove the broken section by making at least three cuts with an iron pipe cutter. Then insert a new section and connect with approved couplings.

Find out if you can use PVC or ABS plastic for the replacement section. The replacement section may have to be in two parts if the hole is tight. Really sounds like a professional job to me.

  • 1
    The problem with verticle cast is once it starts leaking I find it easier in the long run to replace the run. You may find if you replace a verticle section other sections above start leaking. This can turn into a big job fast since others use the same line. If your repair fails before cutting the pipe make sure to get approval or you might be liable for everything above being replaced.
    – Ed Beal
    Commented Sep 6, 2017 at 18:53
  • I have heard that some local codes require multi-unit structures to use cast iron above the slab. I've heard the reason is lack of combustibility of cast iron, and I've heard there is lower noise from cast iron. Which is it? As far as I am concerned only plastic should be used anywhere, unless the liquid being drained is extremely hot. I walked through one "mansion" under construction and noticed cast iron vertical runs from the story above joining to plastic (PVC IIRC) above the slab. I wondered why. Commented Sep 6, 2017 at 23:05
  • We are going to break the concrete around the cast iron pipe that is leaking to see if there is a sleeve. I am doubtful there is one as the cast iron is original from 1978 and the permit and inspection process then as far as code requirements was non existent. If there is a sleeve it should make it a lot easier to remove. I purchased a rotor hammer with a long chipper and drill bit so I don't see the difficulty of making a hole around the existing pipe if needed. Yes, it is a noise issue and all of the plumbers have bid with cast iron. Small pipe, not heavy, no soder, just clamps I can do it Commented Sep 6, 2017 at 23:29
  • Why do you need to enlarge the hole? Is this approved? Just cut the pipe above and below the concrete (two cuts above and two below, so four cuts total), then hammer the middle section out or it may fall out. If you do choose to enlarge the hole or find you have to to get the pipe out or the new one in, then the fire code will probably require you to seal it up next to the new pipe to reduce the potential for the spread of fire. Commented Sep 7, 2017 at 19:13

I got the job done with my handyman. It took 1 1/2 hours to open the walls and cut the concrete and 4 hours to replace the line and connections, which included an hour going to the store to pick up the material. We strapped the pipe on the first and second floor and foamed all of the openings. We did have to cut the 2x6 plate in the wall to make the hole bigger to slide the pipe through as the hole from the first and second floor were not straight and the pipe would not fit through. Took another 1 1/2 hours to close the openings, replace the mirror on the first floor where the wall was opened; and replace shelves that needed to be removed to access behind the bathroom sinks. My lowest bid was $2,800.00 which did not include opening or closing the walls; Total cost with handyman to do everything including parts $927.00

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