Hi all! Have a question about connecting a new shower drain and p-trap(2" ABS)to cast iron under slab. Specifically, what coupling would be appropriate buried underground in this scenario. I cut behind the bell end on the old cast iron horizontal pipe, removing the old cast iron p-trap. Coupling will join the existing horizontal cast iron drain pipe to 2" ABS DWV pipe. My choices are un-shielded couplings (like typical rubber fernco type with 2 bands at ends of coupling) vs a no-hub stainless full shielded coupling. This coupling will be buried below the slab in the bathroom under the shower. So, underground within footprint of house. Which style coupling is correct for this installation? Is a shielded no-hub coupling the way to go?

I posted a pic of a few styles of couplings... from standard Fernco to heavy duty No-Hub shielded.

Also posted is a pic of what I put together with a standard Fernco coupling joining the cast iron to the new 2" ABS.
I just used a standard Fernco in this pic to illustrate the connection I need to make. Nothing is glued up or assembled yet.

I think the shielded coupling, heavy duty or not, is a neoprene sleeve like a Fernco Proflex, which is not rated for buried applications.

The rubber coupling to the right is the same as the strong back 1056-22RC, except the strong back has an additional shear ring in the middle for extra reinforcement. The stear ring can be ordered separately. Both can be used underground and buried. I personally prefer the strong back version.

Thanks! Yes, I did see that the Fernco Proflex is listed as above ground only. I thought the Fernco MD and HD no-hub couplings were rated underground use... but I am looking at the specs and find no mention. Weird. They seem to be full stainless rings and shield.

As you say, the Fernco Strong Back 1056-22RC is listed as underground approval. I have one coming in the mail tomorrow.
Was just wondering if those burly fully shielded stainless no-hub couplings with four straps and the special shield were better connectors for this application. I am kinda confused here. I was reading that some people were against using a regular fernco buried, instead saying that a shielded no-hub was the right connection underground.

So are shielded no-hub couplings only for above ground use to resist shear forces?

I am not a pro just a very active DIYer so may be a pro will weigh in with better info.

I have used the Fernco PROFLEX in above ground applications and the other two for underground applications several times. Since PROFLEX is limited to above ground applications according to Fernco's web site, I concluded (perhaps incorrectly) that all coupling with a thin neoprene sleeve, whether reinforced by two or four SS straps and whether torqued to 60#in or 80#in are for above ground applications. To me the basic difference is one is using a thinner neoprene sleeve and the other two are using much thicker rubber sleeves.

Also bear in mind, the reason to use one vs the other may not only have to do with watertight seal and smooth transition from one pipe material to another, it may also have something to do with the ability of the sleeve to resist abuse from a mechanical snake sent down the drain the clear a blockage and that snake may be fitted with a spinning chain or a cutting head or whatever, may be a thicker rubber will also withstand physical abuse better.

Finally, when I repair or replace a section of pipe, whether PVC or cast, I measure the gap and cut a piece precisely in between. With a thick rubber sleeve, you can slide the sleeve off to one side, fit the pipe in between so there is no gap, then slide the two coupling back over. It is possible to do the transition with no gap at all if you cut the pipe end squarely and measure correctly. With a neoprene sleeve, there is a lip in the middle of the sleeve, so you cannot slide the sleeve over. The thin neoprene must be fitted onto one pipe first, then roll the other side back like rolling a sock, then once the pipes are aligned you roll that end over the other pipe. When you do it this way, it is much harder to do it with no gap, there is always a neoprene lip in the middle and some gap which I personally do not like.



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Thank you, sum. I appreciate your insight and the information. Really helpful!



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Shear ring fernco and support it underneath with concrete