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Replacing Cast Iron Waste Pipe


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Two sections of cast iron sewer pipe in my home need to be replaced due to cracking and splitting from a masonry support shifting. Immediately upstream is a T that goes up to the bathroom sink and vent and continues to the WC. I intend to repair it with PVC. The home was build circa 1950. I certainly don't want to replace any of the upstream piping.

Should I replace all the downstream cast iron piping while I'm at it? It seems to be in good shape but is part of a tangle due to modifications over the years.

If I just replace the two lengths I must fit the PVC into a cast iron hub. Do I use a donut or caulking? I'm am afraid of putting much downward pressure on the pipe with the hub to force the PVC into it.

On the upstream end I will have to put in a new hanger on the end of a T. How do I fasten the hanger between the two joists? Originally there was a piece of wood put between the two joists to which the hanger is attached. I don't see how this piece was fastened in place. I could toenail another piece but I'm not sure that will be strong enough.

You can find a set of pictures here http://home.comcast.net/~cplamb/piping/pictures.htm

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What Scott said, replace all that is accessible in one swoop. Remember the rule of slope is 1/4" per foot for horizontal runs.

Use the correct fittings. There are Tee's and elbows that are not correct to use in drain work. If you don't know, find somebody that knows which fittings are correct and learn from them.

If you can't figure out how to nail something, screw it. [:)]

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  • 2 months later...

I would replace all of the cast iron while I was at it. Sooner more than later it will need it. I would bet that you have more cracks that you can't see. Have you also considered having the main sewer line scoped?

Use Fernco fittings http://www.fernco.com/plumbing/flexible-couplings

Those rubber ferncos are meant for underground work,not inside od a house or building.

You should use no-hub or mission style couplings for exposed work.

As far as cutting out cast iron and sandwhiching a piece of plastic back in there its better to use the same material for a repair on a continuous line,once you come off the main onto a seperate line its ok to switch materials as long as you continue to the end of that line.

I used to see a lot of cast iron 3"-4" stacks where somebody chopped out a chunk of pipe and slid a pvc san tee in there with a couple ferncos then wondered why the stack would look like the leaning tower of pisa after a couple months.

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