Questions about Kerdi shower [Archive] - Ceramic Tile Advice Forums - John Bridge Ceramic Tile


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08-12-2004, 10:07 PM
I just got my Kerdi drain and Kerdi today (thanks Dave), so this weekend is it. We will start the tear out of the old and installation of the new Kerdi shower. So here are my first two (of probably many) questions. Yes, I have already read John's book (well most of it), but I am unsure of exactly how to build the curb.
1. To build a curb do I lay a 2 x 4 on end, screw it into the floor and then wrap it with drywall? If so will the curb be high enough? From reading the book I understand that the pan itself will end up being about 2" above the subfloor, so I want to make sure that the curb itself is high enough.

2. Do I need to staple metal lath to the floor? The shower is a little less than 3' x 4'. If so where do I find it? I have read here of people having trouble finding this stuff, because they apparently hide it in out of the way places in the big home improvement centers (in my case it will be Lowes) and no one who works there knows what it is or its use.

3. Okay, it's my first 3 questions. How much deck mud will I need for my 3' x 4' shower? I will be going to Lowes tomorrow to pick up all of my supplies.

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dave on his knees
08-13-2004, 12:47 AM
Hi ....ok this is just how I do a shower. Your preslope will be about 3/4" at drain and 1 1/4" at wall. It will take about 2 sacks of sand mix (60lbs) along with some additional sand. Buy 3 sacks for insurance. Add 15lbs of sand to each sack of sand mix to get a 5 to 1 ratio. I use a latex additive in mixing the cement. I build my curbs out of 3 2x4's stacked on top of each other, screw each one down on top of the prevous one. I only use lathe on big showers but if u do use lathe don't staple to floor just float it in the middle of the cement. You can cover the curb with sheetrock or cbu is better, Good Luck Dave

08-13-2004, 05:13 AM
The advice I've gotten from this forum when building my Kerdi shower was along these lines:

1. Curb is three 2x4's stacked flat. Cover with drywall if using Kerdi.

2. If your subfloor is plywood - find diamond metal lath (at Home Depot over by the drywall supplies usually up high, also sometimes over by the masonry supplies). Put down 4mil plastic and then staple the lath to the subfloor. Do not float it in the middle of the mud. Don't bother with the latex additive, it isn't needed.

3. Three sacks of Sand Topping Mix (which is about a 3:1 mix) and add another 15lb of sand to each when mixing to achieve a 5:1 mix. (See the Liberry for more details)

I would make the preslope about 1-1/4" at the drain, 3/4" is a little thin, in my opinion.

Read the posts in this thread before you start -

08-13-2004, 06:50 AM
I have seen discussion on that you do not want the matel lathe floated in the middle of the deck because its ends up splitting the deck such that you don't get soild deck. Staple the lathe to the subfloor and if you realy want to float somthing in the middle of the deck try some
2"x2" mesh. (

I sure one of the pros will chime in a beat me if I am wrong. ;)

08-13-2004, 07:01 AM
If i have to do a thin preslope i mix that area with heavier thinset to strengthen it up. :)

08-13-2004, 07:31 AM
Check the Kerdi Directions, if I am not mistaken you will need at minimum 1 1/4" mud at the drain. Make sure you follow their directions so you don't void your warranty! Good luck, I am starting my Kerdi shower next month so I look forward to following your thread.

08-13-2004, 09:55 AM
Actually, I can't find any reference to the thickness at the drain on the Schluter site. Check out this page ( at Schluter which appears to show a fairly thin preslope at the drain. Still too thin for my liking.

I did my shower with 1-1/4" under the drain and three 2x4's for my curb (plus drywall and Kerdi overt that). My shower floor is appr. 3'-6" square and with the slope up from the drain to the perimeter I still have plenty of curb height inside the shower.

08-13-2004, 04:05 PM
Question #4 - What is the best way and what container to mix the deck mud in?

08-13-2004, 04:23 PM
Hi Terri,

I bought one of the black rectangular plastic tubs at HD. It was only a few dollars, find it over by the masonry supplies. I used a regular garden hoe to mix. I would have preferred a hoe with some holes in it (Mason's hoe) but didn't see one at HD. Didn't really matter, just would have been nice.

Anyway, make sure you read the Liberry article on mixing your deck mud. You want it fairly dry. The article describes it better than I can.

08-13-2004, 04:44 PM
Thanks Joe,

We don't have a HD here, so I hope that Lowes has one of those black tubs. I was just looking at your shower thread. I love your big niche. Does it stretch the entire width of the shower?

08-13-2004, 05:02 PM
Hi Terri,

I think Lowes would have a similar tub too. You can mix a full bag of topping mix plus the extra sand(to get 5:1) pretty quickly with the tub. Has a flat bottom and dimensions are about 24"W x 36"L x 8"H.

Yep, the niche goes the full length of the back wall, appr. 50". We really like it, plenty of room for shampoo bottles, etc.

Make sure you post some pichers of your progress!

08-13-2004, 08:58 PM
So, I just returned from SLowes and have almost everything I need. I got stuck at the thinset aisle because I was looking for the recommended Versabond or Master Blend, but all they have are Mapei products. The unmodified thinsets that they had were Keraset and Ultra Contact. Should I buy one of these or head over to the tile store for the Versabond or Master Blend. BTW, who makes those.

Also, I was not able to locate the metal lath. I did find an employee who knew what it was, but had never seen it in the store. Is it necessary for my small shower?

08-13-2004, 09:52 PM
Hi Terri,
Lowes should have Ultraflex II (=versabond) and Kerabond (=masterblend). Ultracontact is more similar to Custom's Marble & Granite Mix. Ultracontact is modified. I would use Ultraflex II if you want a great modified, and use Kerabond if you want their top dryset unmodified. I wouldn't use keraset or Ultraflex I.
Try your yellow pages for masonary supply. They'll have the metal lathe. :)

08-13-2004, 10:03 PM
Hey Terri, You're on late. Well, late on the East coast anyway.

You need the metal lath. If they don't have it you could probably substitute hardware cloth in 1/4 inch, 3/8 inch, or 1/2 inch size. Basically it is metal grid in a roll. Should be near the fencing materials. You could also use chicken wire. The only real problem with these alternatives is keeping them relatively flat. you may have to use more staples than you would with the diamond lath.

Keraset is a fine choice, it is a premium dryset (unmodified) mortar. UltraContact is a polymer-modified thinset so you probably don't want that.

You mentioned a Kerdi shower, are you installing the Kerdi over drywall? If yes, definitely go with the Keraset.

Masterblend & Versabond are both made by Custom Building Products ( Home Depot carries them and I guess Lowes carries the Mapei products.

Any pros around? Please jump in if I'm leading Terri astray!

(Thanks Tom, you posted while I was still typing)

08-13-2004, 10:49 PM
It's not too late here, only 9:43 on the west coast. How come you are up so late answering questions? Thanks for the advice, though. I am sure that I can find hardware cloth or chicken wire. I am going over drywall. We are removing an existing fiberglass base/cultured marble wall shower. Hopefully the drywall underneath is sound. At least it is cheap and easy to replace if not.

08-14-2004, 08:21 AM

Stayed up to watch the Olympics opening ceremony. Now, hopefully you are hard at work on your shower!

08-14-2004, 09:37 AM
Do not use the Keraset.....Use the Kerabond unmodified and either use ultraflex 2 for your modified thinset or else buy a jug of Keralastic to add to your kerabond to make it a very good modified thinset.

Kerabond has a much higher shear strength than Keraset among other things :)

08-14-2004, 09:46 AM
Just to clarify: For adhering the Kerdi to the drywall I use UNmodified thinset, right?
Should I use modified or unmodified for setting my tiles?

08-14-2004, 12:26 PM
Unmodified to bond Kerdi to drywall. Unmodified to bond tile to Kerdi.

08-14-2004, 01:04 PM
We've got the cultured marble walls down. What is the best way to remove the adhesive blobs without damaging the drywall?

08-14-2004, 02:26 PM
Try scraping off with a putty knife or 6" joint knife. If that doesn't work you can try a razor scraper, the wider the blade the faster it should scrape off.

You will probably damage the surface of the drywall but as long as you don't have huge chunks of the surface missing you should still be able to thinset and Kerdi over it. Just make sure you've got any bumps off. The flatter your drywall the better.

John Bridge
08-14-2004, 04:19 PM
Hi Terri,

Often you can just peel the blobs off. You will probably remove the paper, too, but as Joe says, it's really no problem when you're going to cover everything with thin set and Kerdi.

08-15-2004, 05:47 PM
I got the adhesive blobs off. Now I have what I hope is not a totally stupid question. I am assuming I need to use some kind of adhesive to join the bonding flange to the drain pipe, right?

Joe, I really wanted to make a niche like yours the full width of my back wall, but now that we've got the marble panels off I see that there is a pipe running right up the middle of the wall. So I guess that I'll have to do two niches.

David Taylor
08-16-2004, 01:53 AM
You're welcome, Terri. :)

You'll have to add 30 lbs. of sand per bag of Sand Mix (instead of 15 lbs.) to make the ratio 5:1. Adding 15 lbs. only makes it a 4:1 mix.

3/4" of dry pack is all that's required at the drain flange, although you'll hear John and others say they're more comfortable with 1-1/4" of mud there. Since it's your first installation, use at least 1" of mud.

08-16-2004, 05:26 AM
Hi Terri,

The Kerdi Drain comes in either PVC or ABS. Assuming PVC for the drain and PVC for your rough plumbing you would join the two using a PVC cement. You should also use PVC cleaner on the parts to be joined prior to the cement.

I haven't worked with ABS but it appears to be similar to PVC, you just need to use cleaner and cement made for ABS.

When I did my niche I ended up relocating some electrical and telephone cabling.

08-23-2004, 02:04 PM
I have built in my niches with 2 x 4 framing and drywall. Also filled in the area at the bottom of the shower with drywall where the shower pan used to be. My problem is the uneveness where the new and old drywall meet. (I used the same thickness, but it is still uneven) Should I skimcoat everything with thinset to even it out before I put up the Kerdi? Also, despite planning it out thouroughly my niches are about 3/8 inches taller than I want them to be. Can I build that up with thinset before Kerdi? And how much thickness will the Kerdi and thinset take up?

08-24-2004, 12:13 PM
Any answers to my last question???

08-24-2004, 12:29 PM
Building up with thinset can be done up to 1/4" I think. Your niche problem is 3/8" so maybe some "fat mud" would be in order. since the niches aren't tha big an area and your only a bit over the 1/4" I'd probably go with thinset. Wait for more advice on that though as I am no expert.

The uneveness will telegraph through the Kerdi and make setting your tiles a problem. You need to get the wall flat before putting the Kerdi on. How uneven are we talking here? If it isn't too bad you may be able to smooth it out a bit with thinset before applying the Kerdi.

When installing Kerdi the thinset is mixed pretty loose so I wouldn't count on that to fix the unevenness.

08-24-2004, 12:35 PM
The uneveness isn't too bad, that's why I though that maybe a skimcoat of thinset in those areas before I put up the Kerdi might be a good idea. And the niches are 3/8 inch too big now, so how much will the Kerdi and thinset add. Maybe if I build it up about a quarter of an inch the Kerdi will do the rest? It probably would have been easier to put up new drywall in the first place rather than this "patching" I've been trying to do.

08-24-2004, 02:22 PM
Kerdi barely adds about 1/16" of an inch. Unless someone says otherwise, I think you would be ok to build up with the thinset.

John Bridge
08-24-2004, 07:02 PM
Hi Terri,

I often make my niches a little large. Gives me a little play when I'm trying to land a course of tiles at the bottom and top. I would apply the Kerdi and start the tile up the walls, when you get to the niches you can adjust the size then based on where your tiles are landing horizontally speaking. :)

Sometimes 3/8 or a half can be handled by bonding tile scraps to the Kerdi and then tiling over them with you good tile. Trying to build out with thin set is a pain in this case. I wouldn't consider it. :)

09-04-2004, 08:53 AM
I've got the Kerdi up on the walls now. On the 3rd wall I finally felt like I got the hang of it! Now the reason why I am second guessing myself (and it is all the guy at the tile store's fault) I used Kerabond unmodified thinset (mixed like pancake batter :) ), so yesterday I go to pick up another bag of Kerabond - got white this time to protect the manicure - and the tile store guy asks if I want some Keralastic. When I told him no, that the Kerdi specs call for plain unfmodified thinset he kind of gave me a look like I really should get the Keralastic. So all of my Kerabond is mixed with water, and the thing that kind of concerns me is that the dried up blobs that fell off of my trowel onto the floor seems to be sort of crumbly, and when I put a blob in a dish of water I was able to crumble it and get it to dissolve in the water.
So my Kerdi isn't going to start peeling off of the walls is it?
And for setting my tile should is add the Keralastic to the Kerabond, or use water. My tile is American Olean Sandy Ridge. 12" x 12" and 6" x 6" for the walls, and 2" x 2" mosaic for the floor.

David Taylor
09-04-2004, 09:33 AM
That's how the unmodified thinset should behave.... almost to a T. The thinset's not waterproof; two sheets of Kerdi being held together by a thin layer of unmodified thinset is.

Keep on using the Kerabond alone to set your tiles.

John Bridge
09-04-2004, 09:39 AM

I don't use the Mapei thin sets, but I looked up Kerabond and it's a premium dry set which is exactly what Schluter calls for. You are fine. It takes several days for any thin set to get really hard. It doesn't happen overnight.

You didn't give the American Olean series, so I can't find the tile.

If you want to switch brands of thin set, you can get Versa Bond at Home Depot. It is a modified, but I can guarantee you it sets up over Kerdi. I use it frequently.

Hopefully, someone will know more about the Mapei products than I do. :)

09-04-2004, 11:10 AM
David, thanks for the reassurance. :yipee: I thought it was probably ok, but I was starting to have those dreams about tile falling off the walls.

John, here is a link to the tile I am using:
I chose this mainly because the mosaics were VERY reasonably priced at Lowe's, I think it was $2.66 sq. ft., and the larger tiles were also very affordable. We will be selling this house in less than a year, so I needed something that would look good but not break the bank.
Unfortunately, the closest HD is about an hour and a half away. The Lowes here carries Mapei products as does the local Color Tile store, both of which are less than 2 miles from my house and have convenient hours for us DIYers.

John Bridge
09-04-2004, 03:34 PM
David must have posted while I was typing (the sneak). :)

Use the Kerabond as he says. He's done a lot of Kerdi showers himself. :)

David Taylor
09-04-2004, 03:52 PM
Speaking of doing Kerdi showers, I just put the finishing touches on another one - all ready for tiling.

Time for a few adult beverages. Let's see what's left in John's fridge. :)

John Bridge
09-05-2004, 10:30 AM
You will find plenty of Miller's High Life, the champagne of canned beer. :D

David Taylor
09-05-2004, 10:46 AM
Now you tell me - and I was halfways there. :D

Time for another Canadian border run...

09-19-2004, 12:34 PM
I can't decide how I want to construct my curb for my Kerdi shower. the shower itself is approximately 48" x 36", and it seems that stacking three 2 x 4's , then wrapping them with drywall will make a huge curb for my small shower. In John's book he recommends using a single 2 x 4 on end. After wrapping it with drywall and tiling it it should end up being about 4-1/2" high. Will that be high enough considering that the Kerdi drain will be about 1-1/2" above floor level and the sides of the shower will be about 2" high? That will make the curb only about 2-1/2" above the shower floor.
Thanks for all you help so far.

09-19-2004, 12:57 PM
That height would be adequate, Terri, especiall if you're fixin' to have a door or a door-less entry. If you plan to use a curtain, you might want a tad bit more there. I can't tell without some history of your project, which is why we always recommend you just keep adding to your original thread instead of starting a new one. :)

If you're just making a sheetrock curb, that single board on edge might be a little more difficult to stablize than when a fella muds both sides of it. I've never done a Kerdi curb, so I'm just guessing. We'll hope one of the Kerdi guys will stop by pretty soon.

Lotta times the width of the curb will be dictated by the size/style tile trim you plan to use there - more an aesthetic decision.

My opinion; worth price charged.

09-19-2004, 01:04 PM
Sorry about starting the new thread - just lookin for some quick attention :yipee: . We will be putting up glass sliding doors. I guess if I do the single 2 x 4 I'll need to get some pretty long screws. Should I also use some liquid nails?

Here is the link to my previous thread:

09-19-2004, 01:29 PM
:Djust lookin for some quick attention. :yipee: Well, hell, we knew that, you're a girl, ain'tcha? :D

You can drill some half-inch holes down into the top of that board a couple inches and use a 2 1/2 inch Tapcon to screw it to the floor if you wanna. Well, if it's a concrete floor. Or similar length deck screw if it's a wood floor. I looked through your other thread and still couldn't figger out which it is. And I always use construction adhesive in a place like that.

I merged you back in there, though. :)

My opinion; worth price charged.

09-19-2004, 01:44 PM
CX, thanks for the answers and merging my threads. It is a plywood subfloor. I had just thought of drilling the holes in the 2 x 4's before I read you last post.
Here are some before pics of the shower, lovely isn't it?

09-19-2004, 01:48 PM
Here are some pitchers of my progress thus far:

09-26-2004, 02:58 PM
I have the "recipe" for deck mud from the shower construction thread in the Liberry, but I remember reading that I should use something a little different for the mud under the drain itself. Do I change the ratio of the Quikrete Sand Topping Mix and All Purpose Sand, or just add more water to loosen it up a bit?


David Taylor
09-26-2004, 05:03 PM
For that, you'll use the Sand Topping Mix alone and add enough water to make it loose. There's almost a hint of it being shiny. You don't want any standing water when you press the drain into it.

10-04-2004, 03:32 PM
I am a little confused about how high to set the Kerdi drain. In John's book he says it should be a minimum of 1-1/4 inch above the subfloor, but in the picture on the instruction page it doesn't look that high up, AND we cut the hole in the plywood to fit the wider part of the drain so that it fits like the picture, but if we raise it up then the hole is too big. Hope this makes sense. Here is the picture from the instructions:

10-04-2004, 04:08 PM
I'm just a first timer on shower building and kerdi, but the 1 1/4" is for the mud bed. I.e., there will be about 1 1/4" of mud between the plywood and the top of the kerdi drain. Then your mud bed slopes up from there up to the sides of the shower base for a depth that increases by 1/4" per foot. So if your shower is 2 feet from drain to wall, you start with 1 1/4" mud bed at the drain and go up to 1 3/4" at the wall.

I'm sure one of the pros will correct what I've said that might be wrong and will add more.
Mary Ann

10-04-2004, 06:52 PM
I decided to give David Taylor a call (my husband wanted a quick answer), and he straightened me out. We were thinking that the 1 inch or so of mud was necessary towards the center of the drain, but that left us with the outer edge of the flange almost 2" above the subfloor. But David set me straight, so now my poor husband gets to cut down the pipe to a more manageable height. Thanks David!

John Bridge
10-04-2004, 07:57 PM
Hi Terri, :)

You need an inch or more of mud to play it safe. If my instructions amount to overkill, so be it. It's better than having an insuficient amount of mortar that could crack or give at some point down the road. :)

An inch and a quarter is specified for the PVC liner above the clamping ring (which has nothing to do with the Kerdi method, but it's a good benchmark.) ;)

11-19-2004, 09:39 PM
OK, so I did my sloped med bed last weekend. I started to panic, thinking that I would never get the &%^$F& thing smooth, but I relaxed and used the flange on the Kerdi drain to get the slope right and smoothed out the bed. So now it has had a whole week to set and I am ready to apply the Kerdi to the floor. My next question is how do I do a leak test? I know that I don't really have to with a Kerdi shower, but I would like the peace of mind. What do I use to seal the drain?

11-19-2004, 10:55 PM
Hi Teri,

For peace of mind I did a leak test when I did my Kerdi shower. You can buy an inflatable drain plug at HD or Lowes but you should be able to make it work with a decent party balloon too. Just put it in the opening, blow it up, tie it off. Pop it when done. :D

John Bridge
11-20-2004, 10:38 AM
Let the Kerdi job sit a day or two before you fill the floor. Make sure the thin set sets. :)

11-29-2004, 10:37 AM
I finally got around to doing the leak test over the weekend. The pan held water fine, and better yet drained evenly without any puddling. I drained it last night and this morning my Kerdi is dry. The hardest part was finding the right sized balloon! I couldn't find the test balloons at Lowes, so I bought a pack of kids' balloons. It took a while to find a pack of small balloons, since most of the ones I found where the "premium" helium type. Then I had to go back to the store to get a little balloon pump (which also came with those long balloons for making balloon animals) Maybe I can have a new career making balloon animals at birthday parties. :)