mud floor and kerdi drain [Archive] - Ceramic Tile Advice Forums - John Bridge Ceramic Tile


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12-23-2011, 11:48 AM
about to start putting my first mud floor and kerdi drain!

I screwed up and finished the ceiling below so lost easy access to the drain, although not a huge deal to cut a hole in the drywall ceiling below.

Is it worth it to cut the drywall or just put the kerdi drain in from above. The p trap seems a little crooked, so worried about getting the flange real level w/out the plumbing putting pressure on the drain.

2nd question, I've read the min thickness of mortar under the drain is 1 1/4", which sounds thin to me. Is that correct? that would only then put my screed at about 1 3/4"....walls are all about 24" to center of drain.

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12-23-2011, 12:34 PM
Welcome, John. :)

You must get your drain riser pipe plumb before installing your Kerdi drain. How you do it is up to you, but seems like you aughta be able to do that without cutting the ceiling below.

The 1/1/4" thickness at your drain should be sufficient if you have adequate subflooring below it.

If your shower floor is actually square and 4 by 4 feet on a side as described, the rise to the far corners would be closer to 3/4" to achieve the minimum requirement for your slope.

My opinion; worth price charged.

12-23-2011, 01:25 PM
thanks very much cx!

I might can get the riser plumb, then the next problem is the drain line is a little floppy(its all just pvc). I think once the drain is glued in and mortared in, it would be pretty rigid, but was curious how tight the plumbing needed to be...would hate for any cracks around the at drain once tiled.

thanks again!

12-24-2011, 01:49 AM
You're gonna want the plumbing to be as rigid as possible, IMO. If it's loose and flops around, there's always the possibility that the bond might loosen up...and you wouldn't want that.

12-31-2011, 10:35 AM

I think i'd better just cut an access panel in the drywall ceiling below. Patching drywall has got to be easier than repairing a cracked shower drain. thanks again.

12-31-2011, 12:50 PM
ok, thought i had this figured out, not so sure. Been reading other concerns about attaching plumbing after setting the kerdi pushing/pulling to make the pipe connnections potentially damaging the little bit of mortar holding the drain in place.

Has anyone ever screwed the flange of the kerdi drain temporarily until the mortar is setup and the plumbing connected...prior to applying the kerdi?

perhaps I'm making too big of a deal of this. thanks!

12-31-2011, 02:31 PM
If you plan to open up the ceiling anyway, you might try trimming the riser to a good, tight size... test fit it. Now make sure to go into the ceiling and secure the pipe assembly with strapping or something to assure that it doesn't have any upward movement. Now thinset the area around where the flange will go, put your pipe cement on both pipe & flange and twist it in tight.

Couldn't hurt to have someone on a ladder downstairs to help stabilize the whole thing while you're setting it. Check for level....

Make sure thinset oozes up thru the holes in the drain flange. Sponge the exess off the flange and set a water filled or heavy bucket on it and let it cure for at least 24 hours. Make sense? :gerg:

12-31-2011, 03:58 PM
You shouldn't have any trouble as long as you have a partner. One of you holds the drain immobile from above while the other one glues the riser into the drain from below. I think we did the connection several days after putting in the mud bed.

12-31-2011, 04:14 PM
thanks wendy and laz!

laz..if i'm following you, you are suggesting to glue everything in place while setting the drain, right?

You said thinset, but I'm assuming you mean the loose deck mud that I understand needs to go underneath the flange.

I'm thinking I should go ahead and set the drain in the mud bed and give it a day two to cure and with some help or a something better connect the riser and p-trap. I'll use a glue in p-trap, so should be able to connect with only upward pressure.

01-01-2012, 12:48 PM
Jon, it's the "upward pressure" that might be a deal-killer. If the drain is held in with nothing more than deck mud, very possible that the drain will "break bond."

Assuming you haven't set any mud at this point, yes, you can mix up some "fat mud" to pack under the drain. If you want more insurance, I like to mix up some brick morter or "Mason's Mix" a little on the soft side and use that to support the drain assembly. Pack it in until it's completely filled. The next day, it'll be hard as a rock. Sculpt the drop from the edge of the flange nice and vertical. When you go to mud the floor, paint a little loose thinset in this area and the floor mud will bond to it quite well.

If you still plan on glueing the pipes to the flange later on, you still want some weight on the flange while you're pushin' up on it....

01-01-2012, 01:53 PM
thanks, that makes good sense to me, but was concerned about that two step process...seems I read where it was better to ensure all the deck mud (and what supports the flange) to go in all at the same time to prevent cold joints.

So, just so I understand, this is what I'd prolly do:
1) mix up some loose 's' type mortar mix to go under the flange
2) Set the flange height at about 1.75" above floor
3) embed flange in mortar and ensure level
4) sculpt the edge of this 1.75" so it's nice and vertical...maybe stick some pieces of wire lathe while still wet
5) put some loose thinset in this area prior to decking the rest of the floor.

Question..will the mason's mix be supportive enough if only 1.75" thick?

01-01-2012, 03:15 PM
Yep, it's what they put bricks and concrete blocks together with. You'll want it loose enough to force it under the flange and down around it all the way to the bottom, but not enough so that in the outer area of the flange, it "slumps." If it does, just wrap some wide tape around it to hold it in until it sets. Just make sure it oozes up a bit thru the flange holes.

01-01-2012, 11:16 PM
thanks again!
I'll need to go get some stype more then...

Any issue with that cold joint then? Am I interpreting the other directions that the setting the drain and putting the floor should all be done at the same time?

thanks again!

p.s. Is there any reason why straight sand topping mix can't be used instead of s type? What's the purpose for the stype?

01-02-2012, 08:46 AM

01-02-2012, 09:21 AM
In an ideal world, you would set the drain, then mud the floor. Doing it that way, you can mud under the drain flange with deck mud as you do the rest of the floor, so there would be no cold joint.

You asked earlier if screwing the flange to the subfloor would hurt and didn't get a response. I don't think it would hurt anything, but I would use some sort of spacer at each screw location. I would think small blocks of wood would be OK for this. Pre-drill the flange (counter sink the flange, too) and the blocks so nothing will split. Put the screws and spacers where you can get mud in all around them.

01-07-2012, 08:15 AM

What I ended up doing is mixing up some loose 3:1(sand topping mix) and setting the drain in that about 2" or little less. Then mixed up the mud at about 5:1 to set the perimiter.

The perimiter went ok, and is pretty level, but I screwed up and snap lines on the wall too high and had a hard time keeping it perfectly straigt(some minor dips along the wall.) But i think this can be address when tiling.

Then mixed up more mud at 5:1 for the rest of the floor.

It all seemed to come together fine and I don't think i'll end up w/ any cold joints as it didn't take nearly as long as I thought it was going to.

Then set a few pounds of weight on the flange to hold it while everything setup.

I didn't use screws, but I think the kerdi drain flange itself should me molded such that it gives the mortar something to adhere to other than the smooth underside of the flange.


01-07-2012, 08:16 AM
Next question.

Ran out of big pieces of kerdi and I can either piece things together to cover the floor our buy more.

Probably best just to buy more, but thot I'd ask as can't get any now til Monday. The floor is about 51 x 51, so will probably have to have a seam in the floor anyway

01-20-2012, 06:15 AM
ok, ready to order tile and was hoping someone could help with a couple design ideas.

will be using this high def tile that has an incredible likeness to slate and I'll be using this medium color...called autumn or something.

I can get 18x18, 12x12, 3x12bn, 2x4 brick mosaic and 1x1 16x24

First question on bathroom floor. Well lit room, ~6' x 11.5'(tile surface) and am thinking about the the 16x24 in some sort of simple pattern. wife thinks the space is too small for such a large format tile.

what do you all think?

01-21-2012, 01:57 PM
Wife is right. That tile, in my opinion, is too big for that small floor. I have a small floor as well, and anything bigger than a 10"X10" would look funny. Unless if you got fancy and cut a square hole in your large tile and embedded another different color tile in it. That breaks it up a bit.

Of course you could always get a tile cutter and cut the large format tile to smaller pieces, or diagonal pieces, as you go. For a small area like that, it's probably worth the extra time, especially if you are dead set on that particular large format tile.

02-03-2012, 11:37 AM
Sorry, I was wrong. I picked up a book on design and tiling... and it says that large format tiles with small grout joints (reticulated tile) makes a small room look bigger... something to do with not breaking up the space with smaller tiles and multiple grout lines....

Go figure.

02-07-2012, 06:34 AM

Another question. the mud floor is in and now am placing kerdi.

Does it matter what side kerdi is up?

Aslo, can you wash the kerdi? when it arrived, it looked like it had been lying on dirty floor and people walked on it.

Also, I will have to make a seam..does it much matter if the seam is through the drain?


02-07-2012, 06:47 AM
Kerdi can go either side up.

You can brush Kerdi with a moderatly stiff broom, wash it in running water, etc., taking care not to damage the fleece. I would not use any detergents or solvents, though.

Most folks avoid making a seam at the drain. You want to avoid build up at that location.

02-10-2012, 09:09 AM

I can't find my 1/4" 3/16" v any other sizes work for kerdi?

02-10-2012, 11:13 AM
Best is a 1/8"x1/8" square notch trowel. If you have one. Otherwise, get one when you're at the store.

02-11-2012, 12:59 PM
Ok screwed up again.

In putting the first floor piece of kerdi down, thot it would be best to wrap up each wall.

In doing so, I thot everything was fine, but coming back after an hour or so, I notice the kerdi wasn't tight in the corners. I didn't like that, so i said, i;ll just cut that off and put some band around there.

so i cut 3/4" that was wrapped up the wall. in doing so, the floor section came up some at the corners where it was hard to cut.

Am concerned this ruined the bond....i pushed it back down (thinset was still somewhat wet).

will this be ok? Will the residual thinset on the wall (where was wrapped up) be a problem for the kerdi band?

02-11-2012, 06:17 PM
well moving right along.

will start some tiling tomorrow.

question is tile or wall first???

Really need some help on this. Didn't a stellar job getting my screed flat. It's very level over it's length, but has a slight dip in the center.

I can prolly compensate w/ extra thinset for the floor 1x1s. Or am i better off putting in the first course of wall tiles and shimming everything to get it perfectly level?

Next question is bull nose on the outside of shower (no corner) should the field tiles be set first or should I run the bull nose all the way to the top to ensure good, plumb bull nose and the cut the field tiles to fit?


Houston Remodeler
02-11-2012, 11:07 PM
1- It sounds like your floor kerdi should be fine. You'll know tomorrow

2- the extra thinset can be sanded off if you are worried about buildup

3- did you mean floors or walls first? dealers choice. Normally I do walls first as we have mighty strong gravity here in Texas.

4- skim coat the floor with some thinset to fix the birdbaths. let that cure then tile as usual.

5- Dealers choice. I find it easier to work horizontally in rows and climb the wall.

6- can you number your questions? it saves on typing. We aren't paid by the word. Come to think of it we aren't paid at all :bang:

02-12-2012, 10:06 AM
Thanks, Paul...will do!

The kerdi on the floor is probably ok, but here is what I ended up with:

1) one outside edge, for about 6/8 inches did not adhere well and lifts up. Can i just get some thinset under it some how while I put the kerdi band around?

2) I notice another area in the center, maybe an inch sq or so that is a small air bubble or something (sure thot i worked everything down well.) Should I cut a slit and try to get this to adhere down or just tile over it?


Houston Remodeler
02-12-2012, 10:48 AM
1- yes

2- leave it if your tiles are 2" or larger. If smaller, then cut & patch

02-26-2012, 09:33 AM
Sorry folks, just keep messin this thing up!, I think.

Here are some pics after my several hour leak test. The water level stayed constant and had some visibility underneath and could not any problems, but some images give me concern.

I struggled with the floor and wall joint quite a bit and not sure if I have everything right.

First off, after putting kerdi band in the floor/wall corner the first time, after checking after several hours, I noticed what felt like air gaps right in the corner, so got nervous and pulled it off(but it was really just wet thinset!) Anyway, this happend a couple of times in several areas, so ended up putting band back up where I had removed it and tried to clean it up. Here are some pics of the leak test in those areas:

This looks a damp spot right in the center...not sure how this can be?

In this corner i have kerdi band from ceiling to floor, lap joint of kerdi band on floor/wall joint and an inside kerdi corner

This corner is at the curb. The cur is covered twice w/ kerdi, band on the wall/floor joint and then a kerdi inside corner(trimmed to fit). I don't like this corner too much!

This show some migration around drain...this seems consistent w/ other posts tho.

Should/can any of this be removed?


02-26-2012, 09:45 AM got nervous and pulled it off(but it was really just wet thinset!) Anyway, this happend a couple of times in several areas, so ended up putting band back up where I had removed it and tried to clean it up.Jon, you'll never (no exageration) get a proper joint between two layers of Kerdi if you remove an already cured joint and try to Kerdi over the contaminated layer again. You really shouldn't do that.

If the initial installation is done with excess thinset mortar in the overlaps, you can expect more moisture migration into the joint, too. Thinset mortar is not waterproof; Kerdi to Kerdi bond is.

We frequently hear of folks' concerns about seeing discoloration from moisture in some or even all their joints during a flood test of the Kerdi shower pan. But we rarely hear of any leaks unless some pretty gross errors were made at one or more of the joints.

Seeing the joints turn dark is not a comforting thing at all, but if the joints are made correctly the moisture goes only so far and stops and the joints never leak. At all.

What do you do now? After at least 24 hours for your new joints to cure, do another flood test and see if alla water stays in the pan. If it does, I'd continue on with the project. If not, gonna require a Plan B.

My opinion; worth price charged.

02-26-2012, 09:50 AM
Thanks CX!

So, on these areas where I removed and re-kerdi...should I try and remove all the kerdi and re-apply? they do seem to be adhered pretty well.


02-26-2012, 09:53 AM
You can only make it worse at this juncture.

My opinion; worth price charged.

02-26-2012, 11:14 AM
Thanks, it doesn't like a good idea to tear off any kerdi then.

How about putting kerdi over these corners(where wall and floor meet) and such? I had also considered putting very wide band (say 8in up the wall and 6 or 8 inches on the floor) to seal up that corner

know it will leave raised areas and may be excessive on the kerdi, but more concerned about water proofness.

02-28-2012, 06:32 PM
Ok, as you may know, struggled with the floor and floor corners, esp the floor to wall transition.

At about hr 54 of a leak test and here are the results. I can see no water loss.

start of leak test

After about 54 hrs of leak test:

So, regardless of my problems with my corners and things, is ok to continue tiling the floor? I only put an 1.5 of water so.


02-29-2012, 07:37 PM
Here;s the pic after 80 hrs of leak test.


So, an 1 1/2 of water for 80hrs hasn't leaked down at all. I would guess thats good enough regardless of my problems in the corner mentioned above...right?

02-29-2012, 11:23 PM

03-01-2012, 11:15 AM
is it the pic or is that wall piece coming off the wall :shrug:

03-01-2012, 06:16 PM
That is just a piece I taped up. It was convenient and the marking on the scrap piece of kerdi was such I could easily tell if the water had leaked down or not

03-02-2012, 09:44 PM
Meant to post this pic of the drain I took after draining:


To me there lots of wicking of much though?

I used ditra set and unlike my corners, thought this went pretty well.

Should I peel this up some and use kerdi-fix?

The leak test seemed fine otherwise...water level did not drop at all.

03-02-2012, 09:55 PM
Jon, I, for one, can't see what wicking you might be talking about in that photo. Perhaps others can.

What I do see is a seam in your Kerdi directly over the drain flange. Not at all a good idea, that, and cautioned against by Herr Schluter, I do believe.

But as the Tile Buddha would say, "It is what it is."

My opinion; worth price charged.

03-03-2012, 12:09 AM
thanks cx.

I 'think' that seem was just off the edge of the drain flange...but any rate, there is like 8 or 9 inches of overlap on that seam....I had the material and I figured if 2 inches was good, 4 would be better and 8 would be even more better.

the dark area around the drain looked like wicking to me.

So, was wondering if I should get some kerdi fix in that area, or just go ahead and start tiling.


Houston Remodeler
03-03-2012, 07:39 AM

The kerdi fix can't hurt right? Smear some around and get to tiling.

03-03-2012, 09:08 AM
thanks a lot! I'm gettin to it, now!

04-05-2012, 08:52 AM
ok, things are progress, albeit quite slowly!

I laid the the mosaic tiles (litter larger than 1in square) and I must have gotten John Bridge's sequence lay tile then drink beer out of order, cuz I have some issues!

Aesthetically, it probably will be fine, but I had a heck of a time keeping the grout lines between mosaic sheets and especially within (many were cocked and sheets weren't too uniform).

Long story short, there are a few spots that I am now noticing have little or no grout line at all.

I'm using a ceramic, slate looking tile that mimics the texture as well.

The floor has been down for several days and am reluctant to tear it up, I frear it would ruin the kerdi.

Any thoughts?


04-05-2012, 08:56 AM
Mmmm, Jon? We can't see it from over here. :)

04-05-2012, 10:55 AM
You have 2 choices.
1. Learn to love it
2. Tear it out.

Either way, don't grout until you pick one. And if you do decide to replace tiles, there are ways that are less likely to hurt the kerdi and once again kerdi-fix will be your friend. I had to do plenty of individual slice-and-set of my mosaic tiles to straighten them out or get rid of chipped ones. A real pain. :noid:

04-06-2012, 06:56 AM
Sorry bout that! Here is first an overall view of the floor:


Here is a close up of one of the worse areas...I'm not happy with it and disappointed with myself...not sure how I missed!

Anyway, not real easy to tell unless you get pretty close...Not sure what it will look like grouted. So, my questions:

Do these type of issue get better or worse when grouted? (i'll be using a dark gray or black grout)

2nd, Is functionally an issue when there is very little/no grout line?


James Powell
04-06-2012, 07:03 AM
Jon..Did that tile come as a mosiac attached to a backer? Or did you have to set individual tiles?

Houston Remodeler
04-06-2012, 07:03 AM

1- skip the black grout. It will not stay black. The dark grey might stay dark grey depending on the manufacturer

2- No, it will annoy you every time you get into the shower. Peel them up, snad down the thinset and do it again. You'll feel much better.

04-06-2012, 08:49 AM
yes this was a mosaic,,,not sure how i got this scrwed up!

It's been a week now...will that destroy the kerdi?
Hate to ask, but should I just tear it all out to ensure the kerdi isn't damaged?

I was going to use quartz lock grout...I understand the colors wont fade, mildew, that a good thing?

Funcitonally, is there a problem to leave it this way?


04-06-2012, 01:17 PM

04-06-2012, 02:52 PM
The QuartzLock grout is great. You have to let it set for seven days before using it, but it doesn't lose it's colour and never needs sealing.

06-20-2012, 09:12 AM
It would appear the end of the world is coming or hell is about to freeze over!

Friggin finally, I just thinset my last piece of tile on my tile project! I have lots of really good excuses why it took so long if anyone needs any.

As mentioned, planned on use quartz lock, but in just doing some basic research, i have a question.

No problem on the 7 day cure time at all for me. Has it been determined, all the issues with quartzlock traced back to installing too soon and then not allowing proper cure time before getting wet?

I wouldn't mind using sanded grout and don't mind paying for urethane grout either...just want a robust shower. Looks like epoxy wouldn't be good for me...little too technical of prep and use.

Lazarus...have you had any issues w/ quartzlock?

06-20-2012, 09:33 AM
Jon~Speaking strictly from my experience, I've had zero issues with Quartzlock grout.

Yes, I generally allow the tile to set for a couple of days before grouting, but I have grouted the next day over a Kerdi job...and no problem. DitraSet sets up pretty quickly.

07-02-2012, 07:26 AM
Thanks again Laz,

I was about to put the quartz lock when the tile store (same place I got most of my kerdi from) said you cant use quartz lock over kerdi!?!?!

Said same about spectralock, then suggested sanded grout and mixing with grout shield. A quick search suggest that grout shield isn't that great.

Not sure where they came with the issue with kerdi, I see no mention of this on john bridge forums.

I must be over thinking this...surely grouting a shower can't be that complex.

If I just go w/ sanded grout, can anyone recommend a good sealer?

07-02-2012, 08:13 AM
That's certainly the first time I ever heard that. I'd be interested in that tile store quoting something from Schluter specifying that claim. Guess all the Kerdi showers I've used it on are doomed to failure! :shrug: (Not!)

07-02-2012, 08:16 AM
Jon, if they said you can't put QuartzLock or SpectraLock over kerdi they don't know what they are talking about. I put SpectraLock over kerdi all the time in showers. Maybe they just want you to use that Shield stuff. If air can get to grout it should dry. Only time I have ever had a problem with grout drying is slab below grade and it was too cold.

You could certainly use a sanded grout and seal it with something like Aqua Mix Sealers Gold, that would be fine. I would go to another place since this one has no clue about these grouts and applications. I don't use QuartzLock but I only use SpectraLock in showers and mostly over kerdi or Hydro Ban.

Grouting and sealing is still an acceptable way, just so many additives out there they are pushing to make
the grout stain proof by adding it. Does it really work, I am not sold on it the additives like Grout Shield, Grout Boost, etc. Just don't think it has been around long enough to say I would rather go with SpectraLock myself.

They may not know what kerdi really is?

07-02-2012, 11:32 AM
Thanks guys! I'm with the heck could either interact with kerdi anyway? It will never be in direct contact.

Well, thanks for clarifying this!

07-07-2012, 04:21 PM
Ok, Ive done my first area with spectralock and thing seem to be going fine.

I grout some areas that have good 3/16" grout lines first.

I'm now a little concerned bout the shower floor w/ 1" mosaics.

Through some of my own error and defects in the mosaics, I have some ver narrow grout joints on the floor...a couple spots where the 1x tiles appear to be butted.

I also seem to over do it on the thinset and grout lines are'nt very deep as the thinset oozed up on me...probably mixed too loose and used too much!

I did replace many of the more poorly installed 1x and was thinking I was good, but am noticing others. I understand you can't get the spectralock any looser, but could hold off on some of the colorant.

I'm concerned it will be loose enough for these tight joints...1/16th or less.

Also concerned about the few that seem to be butted up...not sure if I can much or any at all in there.

Visually, not too concerned, more concerned about function.

Are there any performance conerns if I continue with specralock on this show floor as described?


07-08-2012, 08:43 AM
just bumpin...

07-08-2012, 09:47 AM
Jon, if you're not prepared to do "overs" on the floor tiles, your only real option is to try to grout what you've got. If the Spectralock won't do it, you'll hafta try some unsanded grout.

You could, I suppose, try to cut out the tightest of the joints, but you take a very large chance on damaging your waterproofing membrane.

My opinion; worth price charged.

07-08-2012, 10:45 AM
Thanks, CX!

I've cleaned the joints as much as possilbe and like you say contemplated use a diamond wheel on a would probably work ok as the diameter of the wheel is close to or less than thickness of tile, and I have some thinset under that.

There are few spot where the 1x are butted up, they are rather inconspicuous and with the color variation, I think it will be too noticeable or bothersome. I was more concerned about function.

Will these joints that are so close and I'm unable to get much grout in going to cause any other functional/performance issues?

Thanks again!

07-08-2012, 12:24 PM
No matter what kind of grout you use, you need to make some space for it. For really narrow joints I like a weird little triangle shaped tool that came with our carbide scraper. Or a utility knife. Even dental tools in spots. Spectralock will fit anywhere unsanded will fit. I have a Roman-style mosaic in my shower and some of the gaps are far less than 1/16". Spectralock went there.

07-08-2012, 04:09 PM

Ok, sounds like i better spend some quality time with the tools you mentioned...thinking about a diamond circ blade and long as I don't shred holes in the kerdi.

I do like the idea of the expoxy spectralock for grout on the floor, so I'll do what is necessary to open up any tight spots.

They been down so long now, I hate to try and pry any up.