Grinding Cast Iron Pipe?

Factual Questions
1

There’s a cast iron soil stack in my basement that descends into the concrete floor. The clean out opening had an iron plug that was rusted in place, and removing the plug tore up the threads on the stack.

I’m no plumber, but it seemed that an easy fix would be to grind away the ruined threads, line the opening with epoxy putty and screw in a plastic plug while the epoxy was setting up.

I tried using a half-round file, some cylindrical grinding stones on an electric drill, and also wire brush attachments
Several hours of work hasn’t come close to removing the remnants of the old threads.

Any advice?

(The iron stack is about 3’ high and the pipe above it is plastic.)

2

IANAP but why not cut off the pipe and use a fernco type coupling to join the cast irno stub and the PVC pipe? Seems a lot easier.

3

If you’re going to epoxy a piece into it, why do the olds threads need to removed?

Rather than epoxy a plug into it, why not epoxy a short piece of pipe with internal threads that will accept a screw-in plug, thus allowing it to be serviced in the future?

4

Filing cast iron is pretty much impossible. You would need an actual stone grinder (angle grinder). And a small one at that to get inside the flange.

Why not just use an expanding rubber plug? Something like this - http://www.shawplugs.com/turn-tite-expandable-rubber-plugs-c-249.html

I bet you could get something similar at Home Depot or wherever.

5

You can’t grind cast iron. The normal process is to scribe and break it, which you also don’t want to do in that spot. I believe the best way would be to find an adapter that would fit into the hole and the other end having the plug. These must be available somewhere as the problem is common. Epoxy the adapter in the hole. They may even make one with an expander to avoid the epoxy.

6

That sounds like the way to go. Thanks.

Mildly amusing detail:
When a drain rooter company came in several weeks back, they took off my crude fix (plastic bag held in place with a hose clamp), and after rooting the drain they attached a plastic cap sealed with a wax ring.

That worked great until the first time someone took a long hot shower.

Gary T:The epoxy fix was supposed to create new usable threads. You either grease the new cap to keep it from sticking, or just gently screw it in to cut the threads and then gently screw it out when the putty starts to harden.

I’ve used that technique before on ruined screw holes in wood and metal, but never on water pipe.

7

[quote=“Baal_Houtham, post:6, topic:551390”]

Gotcha. Thanks for the explanation. Now I’m thinking you could still do this without removing the old threads if the new plug was of appropriate size. Would that work?

8

you may need to goop some epoxy to bring the surface smooth to the height of the remaining threads so that an expanding plug can be inserted without getting torn up and it would have lots of sealing surface.

9

Some interesting suggestions here.

As Al says the there must be a solution ( or more likely several solutions) as it is bound to be a common problem. I assume you do not have a plumber friend or you would just ask them. I’ll be talking to a plumber today so I will ask him his opinion. This is an issue that I have wondered about myself, as I am doing more renovations and could very likely end up dealing with.