kerdi drain questions? [Archive] - Ceramic Tile Advice Forums - John Bridge Ceramic Tile


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02-25-2008, 09:04 PM

Can you attach the kerdi drain to galvanized steel or cast iron pipe. If so, should the plumber install the drain onto the pipe first, and then mud the floor, then kerdi?
There is no access the next leve down from underneath. Everything has to be done from inside the bathroom. What height should the drain be installed above the plywood before the mud goes in?

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02-25-2008, 09:17 PM
If the pipes are galvanized, I'd tear the floor up and replace. If cast iron, depends on how old they are. If they're in good condition, you can probably get away with leaving it.

Safer to replace.

Assuming you have enough vertical height on the riser from the trap, you'd cut it off, use a no-hub connector to attach a pvc or abs (depending on which drain you have), then glue the drain onto the stub sticking up. If you don't have enough height, you'll have to tear things up, find a good place to break the existing stuff off, then transition to plastic.

A mudbed floor needs to be in the order of 1" thick or more at the drain if over plywood floor. If it is a slab, you can make it less. It is critical to seal the drain to the floor with mortar or cement. It is also critical to have the drain plumb.

03-02-2008, 05:58 PM
I noticed in Schluters installation DVD that the installer installs the drain in the floor opening and then I guess they attach the drain trap and piping from the ceiling on the level underneath.

Can you still use the kerdi drain if you have only access from inside the bathroom or if your doing a basement for example where there is no access and you could only work from up top. If so, how do you do it?


Tool Guy - Kg
03-02-2008, 06:24 PM
Absolutely! Take a look at this thread inna Liberry that Mike2 made (

Take a look at the picture "Diagram providing rough-in details". It shows the critical dimensions needed so you can work from the "ground, up" with the plumbing. With the top of the 2" drain pipe at the correct height, it's a simple matter of installing the Kerdi drain on top of it. :)

Brian in San Diego
03-02-2008, 06:28 PM

First of all, the moderators of the forum would like all of us to abide by a "one project, one thread" protocol. I see you started two threads with the same title "slc question" and this is the second thread you've started with a kerdi drain question. Please ask all your questions for your bathroom project one one thread, that way we know what you've asked and the answers you received.

The kerdi drain can most certainly be installed from above. If you are building a mud bed the height of the mud at the drain is determined and then the 2" riser coming from the trap can be measured and cut to length. The drain gets glued to it and the mud bed gets packed around it.


03-02-2008, 06:29 PM
OK. Does it get messy?, when I start putting the mortar around the opening and then start gluing the pipe. MY concern is that I might get a bad connection with the pvc glue or it might dry to quickly (it sets up fast) before I get a chance to level the drain.

How do you check to see if that connection(between the drain and drain pipe) for leaks after the glue dries?

I posted before I got a chance to read your thread. You're saying that I put the drain first and after it dries I pack the mud underneath it?


Brian in San Diego
03-02-2008, 06:39 PM

Dry fit everything first. Sand inside the drain and outside the pipe. Deburr the pipe so you can slide the drain off and on. All the leveling gets done prior to starting the mud bed.

That's correct. Install the drain and after it's dried pack your mud bed. If PVC or ABS glue is used properly there shouldn't be a big mess. You have to thoroughly coat the pieces but they don't have to have glue slopped everywhere.


03-02-2008, 08:15 PM

Just like Brian said, glue in the drain first, and make sure it's reasonably level. After that's finished, you can pack your mud in around it. I usually take a few shovels of my mixed mud and add a little extra water to it, just to make it pack under the drain easier. You dont want it soupy, just a little more damp than usual. Keep a small torpedo level across the Kerdi drain flange because you can easily throw it off as you pack mud underneath the plastic Kerdi drain flange.