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I am in the middle of replacing a drain in the concrete floor of my basement. I'm replacing it because the current drain is terribly rusted, and was quite crooked in terms of not being flush with the floor. I'm getting ready to seal the concrete and figured I might as well put in a nicer drain. Now that I've broken out the concrete around it, I can see that it's a St. Louis style drain, and I'm assuming it's cast iron.

I had been thinking "Why on Earth do they make these water-channeling fixtures out of cast iron when cast iron rusts so easily? I thought maybe that was just how it was done in the old days, but that now you wouldn't see iron being used for plumbing. However, now I'm looking for fixtures to replace the rusted drain with, and I notice a lot of these are made of ductile iron. I know that ductile iron is a different alloy, but does it not rust? I'm looking to install something that won't rust, so I need to figure out if ductile iron is off limits.

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  • Cast iron is a fine plumbing material, especially when your society has not invented a quality plastic yet. Some steels rust much slower than normal steel, Cor-Ten and railroad rails are two examples. Iron rusts much slower than typical steel, however will still rust in presence of a corrosive - don't use iron piping downstream of a soda fountain for instance.
    – Harper - Reinstate Ukraine
    Mar 29, 2016 at 2:22

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Ductile Iron dose rust but at a much slower rate than Cast Iron I only use it when the owner wants the old style piping (Okam and lead) for the seal. I believe it will out last you and any kids if it has a protective coating it will last over 75 years if memory serves but I haven't installed any in years I usually change to ABS and a no hub (also called a fernco coupling). I think the No hub and abs is much easier to install. so those art the 2 methods I use.

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  • Could you elaborate on why an owner would want old style piping "for the seal?" What's better about the seal?
    – bubbleking
    Mar 28, 2016 at 23:51
  • Ductile iron pipes can also be obtained with cement or plastic inner liners, further decreasing the possibility of rust.
    – iLikeDirt
    Mar 29, 2016 at 0:09
  • Or can be painted with epoxy paints to same effect. I don't know about "for the seal" but the closet flange is soldered to the pipe with a great deal of solder with a bond capable of carrying hundreds of pounds, and is certainly not ever going to leak.
    – Harper - Reinstate Ukraine
    Mar 29, 2016 at 2:25

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