Cast iron wall thickness concerns

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RCbuilds

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I'm reworking the DWV in the basement of my 1969 split level for my laundry room. I'm tapping into what was a 4" cast iron floor drain.

I would like to use a mission coupling to tie in my new 4" PVC, but due to space constraints, the only place I could cut into the existing cast iron was the horizontal leg of the old trap. Surprisingly, the cast seems incredibly strong for its age and being underground and wet for 50 years.

My concern is that due to the way the trap was cast, the wall thickness on the top of the pipe is thinner than the bottom where the weir of the trap was located. (1/8" vs. 3/16").

I suppose the only other option would be to remove the remaining cast and use a donut (not a fun venture considering this is 30" under my basement floor). Will a mission be okay on here? I'd appreciate any advice on this. Thanks!

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Reach4

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I expect a donut is OK. A shielded coupling, such as Mission, is OK. A non-shielded flex coupling is even OK since it will be buried. I am not a pro.
 

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Thanks Reach4. I played around a bit with the remainder of the cast iron on the trap that was pulled after I cut them apart. The thinner wall section definitely took some pressure to crack with a pair of pliers, but broke more easily than the normal cast thickness. I'm a firm believer in "do it right the first time".
 

Tuttles Revenge

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Unless the cast iron is paper thin (more or less ish) it will be fine. There isn't a lot of uniformity to older cast iron. Being that its a circle and your shielded coupling will be applying mostly uniform force it should be good. Think of trying to crush an egg in your hand. Shielded couplings OK under slab. Unsheilded not OK under slab inside the foot print of a structure (UPC at least). Insert donut OK under slab.
 
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