# Bathroom floor - Kerdi Band for Ditra / drywall joint?



## Airgibson (Aug 3, 2010)

I'm about to pull up the linoleum in our bathroom and take my first dive into tiling. I plan on using Ditra above the plywood along with Kerdi Band for water-proofing the seams and joints, but the main thing I don't exactly understand is what I'm going to do at the ditra / wall joint. I've looked over the Ditra Handbook, but the details are pretty thin for handling these kinds of joints.

The baseboards will be removed, and I believe I am supposed to leave a 1/4" gap between the wall and the ditra. But as for the installation of the Kerdi Band at the wall joint, I'm just not sure exactly how that is done. Do I just smear some unmodified thinset down on the edge of the Ditra and on the drywall, and then lay out the Kerdi Band as best as possible? Do I push the thinset back into the 1/4" gap as well? Should corner bead be used somehow? I am having nightmares of my base-board sticking out from the wall when I go back to re-attach them later due to the mortar / kerdi being behind it.

The only Kerdi Band installation instructions I'm finding tends to be for water-proofing a shower, so I'm just a little lost on *exactly* how I should handle this kind of joint.


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## Bud Cline (Mar 12, 2006)

OK, here's the deal!!!!!

First of all...why are you waterproofing the bathroom floor to begin with?

In theory this sounds like a good idea maybe but not all that easy to do in reality. Maybe impossible in some cases. 
What about the door? 
What about floor vents? 
What about the toilet flange under the toilet? 
What about the bathtub?

So what's your reasoniong behind this idea?


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## Airgibson (Aug 3, 2010)

That is a great point, Bud. I am under the assumption that this is what I should be doing in the event that we had some kind of sink / toilet leak or large splash hit the floor just to protect the sub-floor from rot or mold (assuming the water gets to a joint). Obviously if something leaks enough, it's going to get to the door, vents, etc... like you said. 

I definitely don't expect to make a "swimming pool" here, but I'd hate to miss out on the extra water damage protection if it's simple to do.

And yes, the toilet would have been my next question. What does the typical Ditra installation around the sewer pipe look like? Should there be any special effort there to waterproof that area it if it was your bathroom?


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## Bud Cline (Mar 12, 2006)

I can tell you first-hand that hotels and motels have been trying to waterproof bathroom floors for a long long time to no avail. Have you ever noticed the marble strips under the bathroom doors? Water dams! But they don't work because there is no way to easily waterproof the door jambs.

To tell you the truth I wouldn't get too excited about it. Your plan is good but you would still have to be there in the event of a spill so you could clean it up quickly. In the event of an unforeseen flood while you were out of town or at work then that's what your homeowners insurance is for.

You can DITRA the floor, KERDI Band the DITRA seams, turn the KERDI Band up the walls two or so inches, caulk around the toilet, caulk the floor to the tub, then sleep comfortably knowing you have taken some measures to avoid a major problem. But to keep a disaster from being shared with the rest of the house is probably not realistic.



> What does the typical Ditra installation around the sewer pipe look like?


You would of course remove the toilet. Under the toilet should be a flange (about 7/14" in diameter) of some sort, there have been many designs over the years. The flange is what seals the toilet to the drain by means of a wax ring seal.

Simply install the DITRA around the flange. That's all you can do. The wax seals the toilet discharge of course. You could then completely caulk the toilets foot print (pedestal) to the floor but this is never recommended. Not a good idea because wax seals have been known to develop leaks also. If the pedestal is sealed to the floor you would not be able to detect that leak. On a second floor that's a problem. When pedestals do get caulked for appearance reasons (and they do get caulked frequently) then the backside of the pedestal is left open so that any leaking water can escape and be detected sooner.

So...do ya see what I mean? One thing leads to another and another and another.


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## Airgibson (Aug 3, 2010)

Yes, I completely understand what you're saying. "No matter what you do, there will always be something bad that can happen which could cause damage in other areas that aren't protected. "

At the same time, I can imagine many scenarios where waterproofing those joints would _definitely_ save your subfloor from rot or mold, so I believe I'll stick to my gut on this and apply the Kerdi.

So back to the original question, can anyone advise me or point me to the actual installation procedure for Kerdi-Band at a ditra / wall joint?


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## epson (Jul 28, 2010)

Here this should help you out: http://www.schluter.com/media/brochures/DitraHandbook.pdf


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## Airgibson (Aug 3, 2010)

Epson, yes I've already got the basic ditra handbook. But regarding the ditra / drywall joint, it only has a picture with pretty scarce details. In the picture, it looks like they're using some kind of corner bead? And I am assuming I spread thinset up on the wall as well as on the ditra?

They mention that sometimes unmodified thinset doesn't work for applying it to the wall, so I was wondering how some of you guys might have handled applying it to the wall.


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## epson (Jul 28, 2010)

You would place the Kerdi-band over the joints with unmodified thinset mortar, just as if you were taping and mudding drywall.

Always use unmodified thinset mortar over Ditra. Deviation from this may cause extended cure times for your floor, and unpredictable results when the floor is subjected to stress. And then apply tile to it. 

Here are some video's that might help : http://www.google.ca/#q=youtube+How...&resnum=1&ved=0CBsQqwQwAA&fp=cda8f90fc8d23ed3


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## Bud Cline (Mar 12, 2006)

OK Air here's the thing...

A few years ago all Schluter KERDI and DITRA was to be installed with modified thinset.

THEN...installations were being wrecked because the building trades are a very very impatient trade indeed. Modified thinset does take longer to cure when it is between two sheets of plastic or a sheet of plastic and an impervious tile. There is little moisture absorption and the thinset must have time to air-cure. Morons were trying to get back on a fresh tile installation to grout the tile before the thinset had cured and their movement was wrecking tile jobs.

So...Schluter comes along and changes the rules. NOW, they want tile over KERDI or DITRA to be installed only with unmodified thinset because unmodified thinset will cure on its own and doesn't require any air, basically.

Suddenly this technique is now gospel and less experienced doers jump on the _"Always use unmodified thinset mortar over Ditra. Deviation from this may cause extended cure times for your floor, and unpredictable results when the floor is subjected to stress, bandwagon."_

While the statement is true it can also be a bunch of hooey, these guys have drank the Schluter orange Kool-Aid and now preach nothing else.

I can tell you that I have NEVER installed tile over DITRA or KERDI using unmodified thinset. I don't trust the stuff. I do wait an extra day for cure and have never ever had an issue.

So here's my recommendation for you.
Forget all that crap. Use modified thinset to install your KERDI Band. You need the Band to lap the DITRA a minimum of two inches using modified thinset. Apply modified thinset on the wall also and roll the Band up onto the wall. It will stay, it will cure in a short time, it will work, it will do exactly what you want it to do. Drag over the surface with a wide putty knife to press the Band into the thinset and be done with it.


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## Airgibson (Aug 3, 2010)

Bob, thanks a lot for that advice. I hope I am not driving you nuts here, but I know the devil is in the details on a lot of this. If you wouldn't mind sharing your thoughts, I had a few more related questions that I know I'm going to run into: 

1) I am putting up some base boards after the tile job is finished. Is there anything wrong with me nailing the board through the Kerdi / thinset, or is that a huge no-no?

2) I have a small inside corner that I will have to deal with when I apply the Kerdi band (and I am not going to get the special Kerdi Corner to deal with it). How should I go about putting it in a corner? Fold down the excess and just thin-set over it? Trim the excess?

3) What caulking procedure would you use where the tub meets the ditra? I am assuming I should use silicone between the ditra and the tub, install the tile, grout up to the tub, and then add another layer of silicone / caulk?


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## JazMan (Feb 17, 2007)

Hi Air,

You might be driving Bob nuts (?), but I'm not sure about *Bud.* Although he might say that he sometimes thinks he is nuts. :laughing:

1. Nothing wrong with that. The nails will be an inch or two off the floor. 

2. Make a corner like the ones they used to supply before they made the formed ones we now use. Cut a square of Band about 4"x4". Make a cut in the mid-point, but only cut it half way up. Then install by folding in onto its self. Hope I xplained so you'll understand.

3. Your procedure sounds good to me.

Jaz


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## Airgibson (Aug 3, 2010)

Doh...sorry about that B*u*d. And thanks Jaz, the corner method you just mentioned is exactly what I just watched elsewhere. I'll do just that.


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## Bud Cline (Mar 12, 2006)

...what he said!


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