AJ's Kerdi Shower Project [Archive] - Ceramic Tile Advice Forums - John Bridge Ceramic Tile


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08-13-2007, 07:57 PM
[first post; been reading for a while; have both of JB's books....but, still have unanswered Q's]

I have a roughed in shower compartment that is approx 52" X 42", and want to order a Schluter shower kit. Is the appropriate tray to buy the 48" sq or 72" sq size. Obviously, the 48" will come up a couple of inches short. However, that 2" gap on each end seems like it could be filled (with mortar).

OTOH, I'm tempted to order the 72" sq pan because it could be cut to fit snugly - if the cutting is done right.

Is this a flip-of-the-coin issue, or might there be a compelling reason to go one way or the other?

thanks in advance

p.s. moderator, if this Q belongs in a particular thread, please move it there

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08-13-2007, 08:20 PM
Welcome AJ. :)

First, starting your own thread for your project is just what the moderators want you to do. :tup2: Bookmark it so you can always find it. Post any additional questions on your project right here.

Kerdi trays can be cut, or extended with mud. But - they have to be extended or cut equally on all sides in order to keep the first row of wall tiles even.

Your best bet may be to mud your own slope and Kerdi right over that. I believe that's what the majority of Kerdi users here end up doing. You can do it too.

08-13-2007, 08:29 PM
what Dan said. :nod: by the time you fiddle around putting that square peg in a round hole you could have the mud floor done, kerdied, and be on to tiling.

08-30-2007, 07:12 PM
A thread to track the progress on our shower project.

Have a post prepared with one pic....but when I submit the new thread, I keep getting an error message that says my post contains URLs that have to be removed. Aside from the pic, I don't see any URLs in my post. I have tried removing various elements, but keep getting the error.

Can someone explain this error? Is there some block that prevents a pic being added during creation of a new thread?


chuck stevenson
08-30-2007, 07:15 PM
The pic is there. It does not show in preview.

Check the Liberry in the dark blue band above.

Nice Arch!

08-30-2007, 07:16 PM
Pic set 1
cement board (CB) and blue board (BB) hung over 2X4 framing. Original idea was to do veneer plaster on upper walls and ceiling, although I'm now told that tiling to ceiling is a possibility (that's what happens when you give "the architect" too much time to cogitate).

set 2
Niches lined with 1/4" CB. A minor (he says hopefully) design flaw in the niches revealed itself after CB was hung: Niche too close to wall, leaving only ~1/2" clearance. Solution (visible in rt hand pic) was to build up thickness with 3/4" of CB. Now have 1 1/4" clearance. I am hoping this allows for a smooth tile transition from wall to niche.

08-30-2007, 07:18 PM
set 3
Kerdi-band hung into vertical corners first, followed by two ~1 meter sheets of Kerdi-mat on back wall. I didn't have the nerve to try it as one sheet, even though width of shower (39 7/8") is almost a perfect match to Kerdi-mat width (39 1/2"). Per JB's book, Kerdi hung directly over niches, and top sheet overlapping bottom by ~2".

The CB really does suck the moisture out of the thinset (btw, using Versabond). As I gain experience, I am mixing it looser, and spraying the walls with water just prior to troweling. Amazing how fast that water soaks right into the CB!

Q Noticed an air bubble (~3" x 3") under the first sheet hung within a few hrs of hanging sheet....toward bottom :bang: . Funny thing was I couldn't feel it today (after 24h setup time). Should I slice the Kerdi and try to fill in around that bubble? I have an idea about putting some thinset into a 50ml syringe barrel and forcing it into a small slit in the Kerdi, then mushing it around and flattening it out.

Comments welcome, please!!


chuck stevenson
08-30-2007, 07:19 PM

You be Quick.

Welcome to the JB Forums.

08-30-2007, 07:20 PM
AJ, welcome to the forum!

I will be very anxious to see your finished work in those niches. Bet they will look outstanding! :)

08-30-2007, 07:30 PM
Thx Marge and Chuck

hope to post more updates by early next week.

08-30-2007, 09:55 PM
I smell a carpenter here - the framing and niches are just tooooooo perty!

Looking good AJ, but really - you gotta slow down! You're gonna make the rest of us look bad. :sheep:

09-04-2007, 12:40 PM
set 4: curb series

Curb built up with 2x4s screwed and toenailed into place; covered with 1/2" CB. To give top an inward tilt, thin end of several cedar shingles glued into place before securing CB. Single piece of Kerdi-mat (4" wider than doorway) wrapped over curb from inside subfloor to outside subfloor; Four Kerdi-outside corners used to for waterproofing.

09-04-2007, 12:55 PM
set 5:

Kerdi short wall near doorway

Single piece (~18" wide) that runs entire length hung vertically on inside, then wrapped around both corners and a couple of inches onto outside wall. This worked very well to provide continuous sheet without seams around doorframe.

Now its on to mudding the floor!

09-04-2007, 01:37 PM
Is that a Better Bench I see in pic set #3? What size did you install? Did you install that as a bench or a footrest? I'm planning to use the BT-17 Triangular Shelf as a footrest for the wife. Looking good and the progress has been quick. Keep up the good work.


09-04-2007, 01:59 PM

That is their BB-24 model that measures ~17+" on the short sides. We will mount it primarily to be used as a seat - altho, don't see why ya couldn't stick a foot up there. Should be around 21" off floor tiles at the end. Not shown: extra cripple studs in walls to accept mounting screws.

Also, Pic set #1 shows nipple sticking out of wall (~36" ht) where a hand held attachment will be mounted. The idea is to be able to sit on the bench and use the hand held to wash feet.


09-10-2007, 02:44 PM
Used Mud calculator and bag directions to come up with Mud mixture as follows
For approx 2cu ft floor mud: use 160 lbs Quikrete Sand topping mix + 70lb sand + 2 gal water. Formula a lil' lean on the amt of sand (calculator said use 78lbs) - but I'd only bought a single 70lb bag.

Anyway, that was too much to mix in my wheelbarrow - so, I dumped it on the floor. When mixed it seemed pretty dry, so I added a couple of cups more water (didn't pay attn to exact amt).


09-10-2007, 02:51 PM
set 6

Screeds and drain in place, filling in rest of floor

Slope came out a bit on the steep side: ~7/16" per foot. :scratch:

09-10-2007, 03:03 PM
set 7

before and after Mud pics

batch was just about perfect size, only had couple of trowels worth left over. :clap1:


Brian in San Diego
09-10-2007, 04:06 PM

09-11-2007, 02:15 PM
Thx Brian.

Q 4 U (or anyone else not partying in Charleston)

I've been reading and searching, but haven't found much of any discussion of the fact that the dry pack mortar surface is kinda rough AFTER it sets. It can bear weight fine, but sandy particles seem to come loose quite easily. I tried to clean up the surface with a hand brush and got more loose material than I was expecting. Vacuumed that up and found I'd created some micropockets. :crap:

In reading various posts I found in searching for a relevant discussion, I came across someone who mentioned "stoning" their mortar bed. What is this technique? Is this like sanding?

If the surface has loose particles, then won't this cause problems spreading the thinset cleanly, flattening the Kerdi over the floor, and bonding the Kerdi to the mortar bed?


09-11-2007, 02:28 PM
You have a lot of company AJ. Most everyone completing their first mud bed posts about the sandy, porous, somewhat loose surface texture. All that is normal. Give it a few more days and it will firm up some. In the meantime, please don't mess with. You'll only make matters worse.

I can't speak directly to what thread you might have read re. stoning, but frequently the use of a 20 grit or so stone to smooth out a floor is recommended. I don't see a need for you to do that however. Whatever little divots you might have created can be fixed with thin-set.

09-14-2007, 01:28 PM
Well, the floor piece of Kerdi mat went in.....not so smoothly though. As I remarked in last post, the mortar floor was prone to releasing debris (aggregated sand grains), and this problem reared it head while troweling the thin set over the floor.

Flattening Kerdi over that bumpy surface was nerve wracking. :sick: The edges of the trowels and straight edge tools I was using kept finding the hard lil high spots those #@%*in' lil' pebbles were creating. Yes, unfortunately in many spots I appear to have created punctures (1-2mm diam) in the Kerdi membrane. They'll have to be repaired. :bang:

After a furious period futilely attempting to smooth the membrane without damaging it, I slumped into my chair and looked over in the corner of the room where I noted a 12" piece of 2" ABS (that will eventually be part of the drain assembly). With 20/20 hindsight, it occurred to me that A ROLLER approach might the best way to squee-gee out the thin-set and smooth the floor out.....and in fact it did work well. While reading threads this AM, I came across one in which (simpsonB, I think....the guy with the beautiful pebble floor) was recommending a roller type device for spreading Kerdi. I've gotta agree...after struggling with my floor piece, in particular. For first-timers like me, a roller is way better than anything with sharp edges or corners on it.

I would welcome, and be interested in a discussion by the experienced folks regarding 1) avoidance of the problems I had with Kerdi-ing over dry pack mortar with loose sand grains and 2) how best to address the punctures I've created in my floor piece. 3) whether I should rip out the floor, get a new piece of Kerdi and redo it entirely.

With respect to the 1st issue, in retrospect, it probably would have been wise to spread some thin set over the mortar and let this harden, then smooth it out with sanding if necessary before laying the floor Kerdi.

With respect to the 2nd issue, Kerdi-banding over the holes is the obvious route. However, is a dab of silicon sealant in each puncture to be recommended?

discouraged :cry:

09-14-2007, 06:02 PM
Sorry to hear your problems, but it does help me with this step of the process in my project. I too have a rough surface on the mud bed so will try to use your roller idea after pre-setting a layer of thinset.

Good luck.

09-14-2007, 08:57 PM
Your experience has been very helpful to me. I was so close to trying to make my own mud floor, but decided to get the Schluter floor and cut it to fit (will do this very soon). Also that's a great tip for using the ABS (I have some scrap PVC around) to roll the Kerdi application.

I'm not so bold as you so I am not installing some things that I would really like, no niches, no bench, no foot rest, no tile detailing, not even using the Schluter strips for the floor to wall and wall to wall joints (really interested in this, just a little too advanced for me right now, I'm using SpectraLoc Grout instead).

How helpful did you find John's Kerdi book? For my simple application, I think the videos and manual are sufficient instruction, suggestions?

Good luck, and please keep posting your progress. I would never have even attempted my project without this website.


09-14-2007, 11:18 PM

I guess I'd recommend the JB Kerdi shower book, ....although with the many Kerdi users on this forum and the Schluter DVD you mention, you can get by, in my opinion. The instruction manual is pretty skippy on details. However, the e-book is only about 10 bucks and comes in handy as an additional reference for many Kerdi related questions. If you like to have read as many opinions as you can find before venturing into unknown territory, then its definitely worth it. It provides lots of sound construction tips, takes you through several Kerdi processes in detail, has good pics throughout, its pretty thorough (except in the MUD related topics). If it falls short anywhere, its in the way of a 'troubleshooting section'. In JB's book, one works with forward momo exclusively....no muffs, no drips, no errors. Not the reality I currently dwell in. :(

But then, ....there is this forum for all those other Qs.

chuck stevenson
09-15-2007, 05:58 AM

Don't tear any Kerdi out. A kerdi-patch is fine. Make it at least 2 inches larger than the tear. you can put a dab of Kerdi-fix or something similar but you really don't need to with the proper overlap.

The sandy surface seems to be the norm. Sweep it well and skim any 'bird baths' with thinset. High spots can be taken care of with a rub stone or a small piece of CMU. If the mudpack is properly checked with screeds of different sizes and floated you should not have those issues.

Here are the pics I posted in simpsonb's thread. These are plam rollers and are used after the Kerdi is imbedded.

Keep up the good work!

09-15-2007, 06:03 AM
it looks as if he did a mud bed after the kerdi. but water will run down that wall some where

chuck stevenson
09-15-2007, 07:49 AM

You are correct. I did the mud bed last. I tiled(less the bottom course) and grouted the walls before I even started the floor beacause I tiled all the way up the 9'6" walls. Tile and grout can be messy. I can sometimes catch it with my hawk, but a good bit winds up on the floor. I did not have to deal with protecting the floor. I did cover the plywood floor with cardboard so clean-up was quick.

One of the benefits of the Kerdi System is it's 100% waterproof if properly installed.

You ought to read the entire thread. It is a step by step on Kedi and Ditra.


It was my first Schleter System bathroom, and will not be the last. I am a convert. No more CBU or liners for me.

Brian in San Diego
09-15-2007, 07:49 AM
Mud bed can be installed last if you so choose. It won't leak because of the kerdi and 2" overlap. No way , no how will it leak...but then agin neither did my greenboard and mastic in my tub surround w/ shower, so pick your method and go with it, Dan.

09-16-2007, 12:38 PM
Installed the Kerdi band at wall/floor junctions and set the preformed inside Kerdi Kereck corners....then I tackled the floor patching task.

Its mighty ugly, so don't expect a pic of that! However, I expect its watertight. Will do a water test sometime soon (after I hook up the plumbing).

So, the Kerdi job is essentially done. Still have to install Kerdi drain part 2 obviously...but I've gotta lot of other building to do before we tile.

Get to build some cabinets now. Hurray! good old wood and glue...and I get to use some tools I've got some game with...

If I :dunce: ever do another Mud floor, I expect I'll do two things different. I'll mix the mud a lil' wetter, and I'll spend a lot of time troweling the damp surface smooth before it sets up.

thx to those who posted helpful comment and encouragment. I really like this forum and its been a great help.
later :wave:

09-16-2007, 03:17 PM
I jus dont get it. I was taught from a bone head like me ya start from the ground up not top to bottom. if you put the pan in last there is a seam there which will have water on it. if you install the pan and then go from there that seem is behind the wall. so i dont get it

09-16-2007, 03:20 PM
Opie, you can do it either way. The seal on the seam won't let any water through. I like to work from the bottom up.