Kerdi Drain - before or after shower pan mud? - Contractor Talk - Professional Construction and Remodeling Forum

bob_cntrctr · 08-01-2009, 04:54 PM

Gentlemen,

I'm going to break down and try a Kerdi drain. Not the whole shower kit - just the drain. The Schluter instructions say the preferred installation method is to mud the shower pan then press the drain flange on top. The drain flange should be installed first only if it's absolutely necessary, and then you should leave at least a one-inch gap for the mud to go under.

What's got me about the preferred method is this: unlike a traditional drain where the flange is under 2" of concrete before you start yanking on it from below to plumb it to the drains, the Kerdi sits on top of the pan. Even with the tiles installed there's nothing but a little thinset and tiles on top of it. Is it not terribly fragile and prone to popping out of the pan when you go to connect it to the drain?

OK, be gentle, I suppose - but that seems am iffy thing to bet the integrity of a shower drain to.

Thanks.

firemike · 08-01-2009, 06:17 PM

I prefer to have it installed first. I set it for the proper slope and then screed the drypack to the flange. Also, that way you are assured it is level, sometimes you have to secure a longer run of PVC pipe below the floor if it is in a basement or crawlspace to prevent flexing of the drain line and hold the flange steady and keep it from moving up and down. Once I had to cut a couple pieces of plywood with a 2 1/2" hole in the middle and screw it to the underside of the subfloor to fill in the 7" hole (so I could pack the entire underside of the flange with mud) the plumber cut for the 2" drain line. He didn't realize that the flange did not sit on the subfloor....

I have never tried to install the flange after the mud, I suppose it would work if the pipe was cut off at exactly the right height and the pipe was solid enough to press the flange on it without it pushing it downward.

jarvis design · 08-01-2009, 08:50 PM

I always install the drain when I am doing the base.
I first make sure the pipe is cut to the correct height.
Just remember to add a little water to the dry pack mortar you are putting under the flange, put down a little more than required, and push the drain into the mud. You should squeeze out some mud if done properly. Make sure you get enough mud under to completely fill the void - that way it is 100% solid.

JazMan · 08-02-2009, 12:23 AM

Bob,

I think you're confusing how it's done. The option to install the drain "after" is if you're using the shower tray and of course if you easily get to it from below. If you're building the floor with deck mud, you need to install the drain at the same time.

Jaz

bob_cntrctr · 08-02-2009, 07:01 AM

Jazman,

Sorry - by "after" I meant what you and Jarvis describe - lay down the mud then press the flange into it. Schluter also suggests the option of pre-installing the flange on the drain pipe, leaving a gap to the floor to later pack mud under it.

Jarvis describes having the drain pipe already in place and pressing the flange onto it when mudding the pan, which I suppose eliminates my worry of later yanking on what I expect to be a fragile bond between the flange and the surface of the pan. Take some careful prep to get everything prepped so that all heights match up with the pipe vertifcal so the flange ends up horizontal though...

JazMan · 08-02-2009, 11:43 PM

Let me try to clarify what I meant. I don't really do it the way you said.

".......lay down the mud then press the flange into it."

I don't think you can really do that, the deck mud would fall down the hole. You start placing the deck mud, then place a ring of the wetter mud where the drain will go, then glue the drain in place and finish the deck mud by filling under the drain.

Jaz

bob_cntrctr · 08-03-2009, 01:39 AM

Thanks for the info, Jazman (Jazman - a reference to Carol King's song of the same name?)

I suppose there are many ways to end up with the desired result.

I'm not sure what the real difference is between ".......lay down the mud then press the flange into it." and what you describe - except that I'm undoubtedly describing poorly 'casue what you write is just about what I meant. Lay down the mud around the drain hole, then press the flange into it.

Except I where you say "..then glue the drain in place and finish the deck mud by filling under the drain.." - which sounds like pretty close to pre-installing the flange and then filling under it, except ou've got a bit of mud under there already.

Anyway - here's what Schluter says in their literature:

http://www.schluter.com/media/brochu...ndbook2008.pdf

page 14, Shower Assembly with mortar base

"...Place a ring of loose mortar up to the inlet hole in the floor and firmly press the drain into the mortar..."

http://www.schluter.com/print/8_2_ke...tallation.aspx

Shower Bases Constructed with Mortar

1(a) If there is access to the plumbing from below, and the waste line will be connected subsequent to installing Schluter-KERDI-DRAIN, the drain can be firmly embedded in a ring of loose mortar and leveled before placing the screed.

2. The screed is then placed flush with the top of the trapezoid-perforated bonding flange of the KERDI-DRAIN.

So it seems that what they prefer you do is lay down some mortar around the hole, then press the flange into the mortar - no drain pipe yet, that's to be added later But noone's so far said that's how they actually do it! Maybe there's a reason - like my originally posted concerns about attaching the drain pipe to the flange held in by what seems so little.

charimon · 08-11-2009, 06:27 PM

I have made several installs this way. The problem with the kerdi drain and a traditional pan is kerdi is designed to:

A, sit atop the slope of the bed and has no provision to lock in to the PVC pan

B, have the waterproof membrane on top of the bed.

What is cool about the Kerdi is the ability to adjust the square drain to match the tile.

My Installation technique is

1. Dens the walls leave 1 " open to the floor

2. Staple to the floor expanded metal lath

3. Set the curb

4. Set the Kerdi Drain

5. Dry pack the floor to desired slope

Wait to cure

6. Use Bonsal B6000 and polyester fabric to build out the water proof membrane bring it up 4"ish on the walls and if you are tiling the bath floor hit the outside corners and wall (where there will be tile) of the curb

Wait to cure or you can $$$ up for the new Mapei http://www.mapei.it/Referenze/Multim...nse_TDS_EA.pdf Which allows setting tile in less than an hour.

Note: With the dens on first, you can mark your level line around it and pack your bed to the line. Even though your dens is embedded in the mortar bed you wont have to worry about possible wicking issues because the waterproof membrane is over the joint.

Thanks Craig

jarvis design · 08-11-2009, 06:36 PM

Quote:

Originally Posted by charimon

I have made several installs this way. The problem with the kerdi drain and a traditional pan is kerdi is designed to:

A, sit atop the slope of the bed and has no provision to lock in to the PVC pan

B, have the waterproof membrane on top of the bed.

What is cool about the Kerdi is the ability to adjust the square drain to match the tile.

My Installation technique is

1. Dens the walls leave 1 " open to the floor

2. Staple to the floor expanded metal lath

3. Set the curb

4. Set the Kerdi Drain

5. Dry pack the floor to desired slope

Wait to cure

6. Use Bonsal B6000 and polyester fabric to build out the water proof membrane bring it up 4"ish on the walls and if you are tiling the bath floor hit the outside corners and wall (where there will be tile) of the curb

Wait to cure or you can $$$ up for the new Mapei http://www.mapei.it/Referenze/Multim...nse_TDS_EA.pdf Which allows setting tile in less than an hour.

Note: With the dens on first, you can mark your level line around it and pack your bed to the line. Even though your dens is embedded in the mortar bed you wont have to worry about possible wicking issues because the waterproof membrane is over the joint.

Thanks Craig

Craig, You mention the problem with the kerdi drain is

A, sit atop the slope of the bed and has no provision to lock in to the PVC pan

You do not use a PVC liner when doing a true "Kerdi" install

B, have the waterproof membrane on top of the bed.

That is the whole point of using the Kerdi system - waterproof right under the tile itself.

Finally, Dens Shield is not 100% waterproof. The only way to create a waterproof assembly is to use Kerdi or another waterproofing product.

charimon · 08-11-2009, 07:06 PM

I understand that what you are saying. But based on the first line of the post....

"Gentlemen,

I'm going to break down and try a Kerdi drain. Not the whole shower kit - just the drain."

I was under the impression that only the drain was purchased. not the system as a whole. my response was how I have installed just the drain in showers for clients.

Also if you look at item 6 i refer to a couple different waterproof membranes.

Thanks Craig

Bud Cline · 08-12-2009, 05:32 PM

I'm not going to read all those above posts so forgive me if I am parroting someone else.

You want the drain FIRMLY INSTALLED BEFORE any mud goes down. The KERDI drain requires about a 3-1/2" hole be cut in the subfloor if you are going to keep the final elevation of the drain at a reasonable level. If you stub up a 2" (or 3") pipe and expect to fill the floor with deck mud then stab the drain you are kidding yourself. Install the drain rigidly to the desired elevation THEN add the mud. It is easy enough to pack the mud around the drain cup and under the drain flange. No big deal.

To install the drain without the egress attached is also asking for big trouble. Especially if you are leaving the hook up to someone else. That drain sitting atop that mud is just too fragile to be screwing with after the fact.