How to get Kerdi shower drain into cast iron flange base?

[tekoa]

I'm a DIYer remodeling an existing bathroom. My plan is to use Schulter's system for waterproofing including the appropriate Kerdi drain. The old shower drain flange might be hard for me to remove. In large part, because I don't know how it is attached.

I looked at the Kerdi Drain with Residential Adapter. It seems ideal for a four bolt (square pattern) setup. But I have a three bolt hole (triangular pattern) existing flange in the concrete subfloor. The drain base holes are 3 inches apart in a triangle pattern as shown in the link below. There aren't preset holes for this pattern in the Kerdi adapter ring.

https://imgur.com/a/Mi6iLtV (link to a picture of my existing drain base)

Looking at the Schulter Drain Residential Adapter CAD drawing, I see that if I drilled my own holes into the adapter ring, I would have to drill right into the center edge of the adapter ring. That area seems to be only the orange rubber gasket section. There isn't any metal backer in that area. I don't want to cause any water leaks by leaving too little supporting gasket to create the seal.

What can I do to get a Kerdi drain into my shower setup?

Should I:

1. plan to have this existing drain base removed, then use a different Kerdi Drain kit? What documentation is there on how to bond a Kerdi drain to cast iron? Is this where I should consider a service weight gasket (Fernco donut) style setup somehow to attach some Kerdi drain to the pipe?
2. Should I drill holes in the Kerdi adapter ring and hope that small amount of gasket between the edge and my new holes is enough to keep things water tight?

I appreciate your help.
Thanks, John

 

[mike fiore]

if you have access to underneath i would cut out old base and fix floor then attach kerdi drain to cast iron with no hub connector 4 or 2 band type. Thats without seeing underneath or whole base. Basically youre #1

 

[tekoa]

if you have access to underneath i would cut out old base and fix floor then attach kerdi drain to cast iron with no hub connector 4 or 2 band type. Thats without seeing underneath or whole base. Basically youre #1

Thanks Mike. I should have mentioned this is in a concrete slab so I don't have access underneath.

I figure removing old base was better. But that may mean for my skill level I need a plumber to remove the old base and attach the new Kerdi drain correctly.

What are most common ways the (cast iron?) base/flange would be attached to the drain pipe? Would removing more concrete around the edge and a pry bar get the removal job done most likely?

 

[mike fiore]

slab is tough . in that case i would would remove base and flange. and use shluter stainless steel adapter to connect to cast with a no hub connecter....I dont know of any other options if you want to use shluter system.

 

[tekoa]

slab is tough . in that case i would would remove base and flange. and use shluter stainless steel adapter to connect to cast with a no hub connecter....I dont know of any other options if you want to use shluter system.

Thanks again Mike. I'm learning about no-hub connectors for the first time in the last 36 hours. I hadn't realized what that Kerdi drain no-hub outlet style was even for.

So I guess I'd need to drill up concrete around the drain pipe to make room for the no-hub connector.

So this would be a no-hub connector with a metal shielded piece, and not the flexible coupling style I'm assuming...

 

[Mikey]

I did that in Florida. Cut out enough of the slab to use the Kerdi drain into PVC, then conventionally into the old house system. The hard part was profiling the slab to the proper slope.

 

[mike fiore]

Thanks again Mike. I'm learning about no-hub connectors for the first time in the last 36 hours. I hadn't realized what that Kerdi drain no-hub outlet style was even for.

So I guess I'd need to drill up concrete around the drain pipe to make room for the no-hub connector.

So this would be a no-hub connector with a metal shielded piece, and not the flexible coupling style I'm assuming...

Exactly..give youreself extra room to fit together but also make sure you backfill for support

 

[chiraldude]

Maybe a dumb question but is it necessary to have a waterproof barrier around the drain in a cement slab? Cement and mortar don't care about water and the only thing below cement is soil.

 

[mike fiore]

yes because if it gets wet it will create mold.

 

[chiraldude]

I guess I still don't get it. Mortar gets packed around the drain flange level with the slab then thinset then tile then grout.
Where would mold have a place to exist? Under the slab around the cast iron pipe? How would it affect the living space with concrete, mortar, thinset, tile, and grout in between?
Unless there are cracks in the slab but then you should use an isolation layer like ditra not the thin kerdi membrane.

 

[mike fiore]

youre right ...with tile no moisture would get through and no membrane would be needed

 

[tekoa]

Here's where I'm at. I abandoned connecting to the top and opted to replace down to the p-trap. I've dug down to the p-trap and to the horizontal trap arm.

While using PVC primer and cement, I realized I only did a coat of cement on the coupling but not the pipe itself. How important is that coat of PVC cement on the pipe itself?

 

[Mr_David]

Maybe a dumb question but is it necessary to have a waterproof barrier around the drain in a cement slab? Cement and mortar don't care about water and the only thing below cement is soil.

cement is the bonding agent in concrete.
You mix cement with sand to make mortar and sand and gravel to make concrete.
If you don't put down a waterproof membrane under tile it will leaker out to the surrounding wall enclosure
Tile grout is not water proof. It cracks and often separates.

 

[Mikey]

Maybe a dumb question but is it necessary to have a waterproof barrier around the drain in a cement slab? Cement and mortar don't care about water and the only thing below cement is soil.

Yes.