First post...first shower. [Archive] - Ceramic Tile Advice Forums - John Bridge Ceramic Tile


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12-22-2016, 08:36 PM
I want to start by thanking all the contributors to this amazing site. What a treasure trove of in to that I am so thankful to have found.

I kind of wanted to lay out my plan and open it up to any recommendations, warnings, or tips that anyone might have. Also have a few specific questions that I cant seem to find definitive answers to.

This shower will be built on a concrete slab. I have purchased a kerdi drain, and will be using hydroban (or other liquid membrane) for the liner and wall/niche sealer. I have lined my studs down to the floor with 1/2" hardibacker, and lined my one exterior wall with felt paper. I will mesh tape, and seal my seams with thinset. I was planning on pouring a concrete curb...wall to wall with a few 3" Tapcon screws drilled into the slab to keep it in place. Is this overkill, or will pouring the concrete over a layer of thinset be sufficient? Is a concrete curb even recommended? I dont like the idea of setting bricks.

I was planning of setting my drain about two inches off the floor to ensure adequate thickness at the drain. Is any reinforcement recommended within the bed at this thickness, and is the recipe for the mud any different whan using a liquid membrane? Also, I have read a few posts about pouring a loose mud around the drain, and packing it in good, but cant seem to find anything about mud thickness above the bonding flange. I will, of course, pack my deck mud on top of a layer of thinset before it dries.

I have a few more plumbing issues to straighten out befor I start mixing any cement, but thought I would throw this post up and see if I am on the right track. I am sure I will have more questions, and appreciate any feedback on my proposal here. Thanks

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12-22-2016, 09:10 PM
Welcome. Please change that permanent signature line to a first name for us to use. :)

I'm unclear why you would have "lined [your] one exterior wall with felt paper" if you intend to use a direct bonded waterproofing membrane on the inside of your shower. You really don't want to do both if I understand what you mean by lined.

You can pour a concrete curb if you like, but I recommend against it. You're likely to have much better luck using CMUs to build the core of a curb. The concrete will have more of a tendency to crack as it cures.

When using a bonding flange drain over a concrete subfloor, I generally install the drain with the flange about 3/4-inch above the slab. I find that allows sufficient room to pack mud under the drain when placing the floor. There is no reinforcement needed for the sloped mud floor, just bond it to the concrete with a slurry of thinset mortar or pure Portland cement.but cant seem to find anything about mud thickness above the bonding flangeI'm a bit confused by that, too. There will be no mud above the bonding flange in a receptor made with a direct bonded waterproofing membrane.

And while we're on the subject of the receptor, let me recommend that you use a sheet-type membrane at least for that portion of your project and it would be best to use the same membrane for the entire shower.

My opinion; worth price charged.

12-22-2016, 09:47 PM
Thanks for the quick response!!

This exterior wall runs the length of the bathroom... which will all be tiled. Only about the last 3 feet of it are in the shower, and it is the back wall, furthest from the shower head. I thought that in such a hot, humid climate (Coastal NC) I would want some sort of condensation barrier between the cold CBU and the warm, damp outside air. I have read conflicting info on this subject. It is definitely not too late to remove the felt if that is recommended.

I was wondering about the concrete cracking as well. Building a CBU core? Layered like a cake with thinset?

3/4 of an inch seems far too thin. Any concerns with making the bed thicker? So the mortar is packed under the drain, packed into the bonding flange, and then floated flush with the top of the flange?

I was really hoping to use only the liquid membrane to keep things simple. Are you saying that I can use a sheet just for the drain area? I havent really done much research on sheet membranes as I was hoping to not have to use one.

12-22-2016, 10:11 PM
Check with your local code compliance officials about the rest of the wall, but do insist that you not be required to have any vapor retarder behind your CBU that has a waterproofing membrane on the other side.

If your code requires a vapor barrier material on the inside of the stud walls (I don't know your local climate or code), the felt paper would not qualify anyway. Building a CBU core? Layered like a cake with thinset?Not CBU, CMUs. Concrete Masonry Unit. Bricks, concrete blocks, etc, bonded together with masonry mortar or thinset mortar.

I think you'll find that 3/4-inch is quite adequate, but use whatever you want. You still must slope up a minimum of 1/4-inch per horizontal foot to the farthest corner of the shower and you'd like to keep the total thickness at 2 inches or less.

You can use the liquid if you want, of course, but don't be thinking it will make things easier. Getting the manufacturer's required thickness of those liquid-applied membranes on all the surfaces without any voids or thin spots is not as simple as might be implied in the literature. This is not like painting the living room walls. On your shower walls it's not so critical, but I would never recommend making the receptor with those materials, although lots of folks do.

My opinion; worth price charged.

12-22-2016, 10:13 PM
The 3/4" around the drain gives you thickness as you do your minimum of 1/4" per foot slope to the drain. The mud would be 3/4" under the drain flange and greater than 3/4" of an inch as you move further from the drain.

12-22-2016, 11:18 PM
If you're using a Kerdi drain you'll have to use Kerdi membrane or another sheet type waterproofing for the pan. Trying to make a liquid membrane and Kerdi drain work together won't end well.

12-23-2016, 09:45 AM
There are some instructions for using liquid with a drain such as a Kerdi or Laticrete drain. I'm not sure if they're manufacturer-sanctioned, but I certainly wouldn't recommend them to someone on their first shower.

Years ago I did a couple of "hybrid" showers with Kerdi on the floor and a liquid membrane on the walls. I will say that it made the walls a lot flatter since there were no membrane overlaps, but in retrospect I would have felt better using one product over the whole shower.

I would recommend the same for you, Kevin. Pick one product that you can use, and use it over the entire shower.

Incidentally, I've been making my curbs out of solid concrete for years now, and not one crack. :D

12-23-2016, 12:40 PM
If you're wanting to use liquid waterproofing on the shower pan do a little research on divot method pan.

12-24-2016, 09:22 AM
After the suggestions received here, and following a bit of research, I have decided to go with the kerdi membrane. Looks pretty fun to do actually! I feel pretty confident about the process, however I would like to find some tips on applying the membrane to custom shower niches. Also, it nseems that I see lots of videos of people doing the walls before the pan. Does it not make more sense to run the pan membrane up the walls a bit, then lap the walls over that? Seems like one would want to start at the bottom and work your way up, like siding, or shingles, so water has no opportunity to run behind seams?

Still a bit uncertain about the moisture barrier on my exterior wall. Feeling now that I might remove it so that any condensation that might occur will have the opportunity to dry out rather than being trapped between the CBU and felt.

I still feel that 3/4 of an inch at the drain is too thin. Since I have no plumbing access once the drain is set, it also seems like it will be tough to get the mortar all the way in there around the center of the drain. Is this not critical as long as there is adequate, even support around the flange? I know that I heard a minimum of 1" thickness on a wooden subfloor...why would thinner be recommended on concrete? Will the bed be more prone to cracking if the overall thickness exceeds 2"?

I think I would still like to use solid concrete for the curb, and a very low profile corner bench. Kevin, Do you have any suggestions or recommendations on this? Reinforcing, bonding, sealing with Kerdi etc?

Thanks for

12-24-2016, 11:42 AM
Make your drain height as high as you like, Kevin, but I find it quite easy to pack mud under there with only a 3/4" clearance. I generally use the edge of a wood float to do the initial part closest to the drain.

Nearly all my shower receptors are over concrete slab foundations with no access to the plumbing from below.

You might also wanna look into USG's waterproofing membrane ( A bit thinner and easier to install than is the Kerdi in my estimation. All the components available on Amazon.

My opinion; worth price charged.

12-24-2016, 11:54 PM
I'll second the recommendation for the Durock membrane.

And I typically make my curbs the same height as if they were three 2x4's with a 1/2" backer on top, so 5" tall or less, and the thickness of the wall with board on both sides which is always 4 1/2".

Of course, a bit of slope on the top toward the inside of the shower, and a couple of pieces of rebar to stiffen it up, and bond it to the slab with thinset.

12-25-2016, 08:19 AM
I used kerdi on my shower. It was easy to install. I placed the sheets of kerdi vertical on the walls, side by side (butt joint style). After that I went over the joints with some of their 5 inch wide strips. This all connects to their kerdi-line drain. I also have my shower on a concrete slab.

The only issue I ran into was too was user created. I had too much kerdi membrane build up on 2 of my inside corners.

12-30-2016, 11:22 PM
Finally getting back to work on the shower after back to back plumbing debacles. Pulled the felt paper down and continued on with framing, niches, and hardiebacker. Hoping to form and pour my curb tomorrow.

Having been reading up on Kerdi, I am now of course second guessing my use of hardiebacker... Or maybe Kerdi?! I know, I know...just wet it and you'll be fine!! Seems to be a fair amount of folks having trouble with these two.

The Durock membrane looks interesting. Might this be a more foolproof method over hardi? There seem to be options for adhesives...including their specially formulated one. Would that be the recommendation? Don't like the silicone caulk corner sealing though.

Still leaning toward the kerdi since I already have the drain, and some of them fancy corner pieces!

Or maybe I take three steps back and just hydroban the whole thing!!

Kevin, How many years has it been since you did those hybrid showers? Having trouble getting that idea out of my head too!

Houston Remodeler
12-31-2016, 08:45 AM
"priming" ceement board with watered down redguard before applying kerdi is a great idea. a 1 part rg to 5 parts water makes the surface of the RG suck in far less water.

Watch this video ( in the spirit of the holidays, try not to snicker at the hair.

01-07-2017, 09:07 PM
Been pretty slow going on the bathroom of late. Two kids under four will chew up time like nothing else!

I hate to sound like a wishy washy little baby, but I am really uncertain which is the best way to move forward after I get the mud bed set in the coming week. Althoough I have read a good deal of the Kerdi Shower book, and watched a fair share of install videos, I am quite apprehensive about laying kerdi over this hardi. Had I done my research beforehand, I would have just used drywall, but since the hardi is all set, I want to leave it up. I have read about wetting it, priming it, and both, and was hoping to get some input from someone that has had consistent, reliable success with any of these methods. I hate to use yet another product that I am unfamiliar with underneath the kerdi... which I have never used either. I also dont want to use nothing but water and end up struggling to get the kerdi up before the thinset dries out...again, first time using it. Truth be told, I am a bit concerned with laying the kerdi in the niches, and footstool.

I am still considering the (hybrid) method, utilizing kerdi on the mortar bed, and hydroban or redguard on the walls. Is one of these products more compatible with kerdi than the other?

I also had a question about what to do where the kerdi ends...assuming I go the kerdi route. I am tiling the entire bathroom and the tiles on the front and rear of the shower will continue down the wall. Is there a special procedure for "ending" the kerdi?

Anyway, here is a pic of my current progress. Been holding off on setting my drain til I am ready to set the bed. Kids would likely be in there climbing all over it! Any input is greatly appreciated. Thanks

01-07-2017, 09:30 PM
Geez...just read that I am not supposed to embed the hardi in my mud bed...uhg. Any advice? Seems like I am working in circles here

01-07-2017, 10:02 PM
Such a dummy. To be sure I will soon be laughed off this site:D

01-07-2017, 10:16 PM
Nobody will be laughing at you, Kevin. John Bridge started this website to provide the DIY visitor with information that will promote the completion of tile installation projects in compliance with local building codes, tile industry standards and manufacturer's installation recommendations. If you already knew all that you wouldn't have come here, eh? :)

You are correct that James Hardie does not permit his Hardiebacker to be embedded into the final deck mud in a traditionally built shower receptor. In your case, where your entire shower is to be covered in a direct bonded waterproofing membrane it is perfectly acceptable for you to have embedded your wallboards in your sloped mud bed.


As for installing your Kerdi membrane over the Hardiebacker, you just need to be sure the surface is damp before you do so. The term for what you want is Saturated, Surface Dry (SSD) and is a term d'art in the construction trades. You want the surface fully damp, but not wet. Spraying the walls with a spray bottle or a garden sprayer filled with water will do the trick handily. No standing water, no shinny wet surface, but the whole board damp. You should have no trouble at all installing your Kerdi membrane.

My opinion; worth price charged.

01-07-2017, 10:49 PM
Phew. Thanks CX. Appreciate the bid of confidence also.

Was thinking that it would not be an issue. Should I try to prevent the hardi from drying out my deck mud too quickly? Should I dampen the bottom section of the boards before I pack in my deck mud? Or skim it with thinset while I do the concrete floor? Or both?

01-07-2017, 10:53 PM
Wouldn't hurt to dampen the bottom of your Hardibacker before you place your deck mud, but you don't wanna add any thinset mortar there. You're not trying to bond the deck mud to the walls.

My opinion; worth price charged.

03-05-2017, 08:28 PM
Geez...almost two months since my last post. Slow going over here eh! Got the mortar bed in about a month ago...that was a fun project and I enjoyed the process quite a bit. Was honestly looking for a reason to tear it out and do it over, but was just too happy with the results, so moved on...slowly.
Had to gather some funds to purchase all the Kerdi, and all the bells and whistles to do it as easily, and fool proof as possible. Almost finished up with that this weekend. Although I was quite nervous about setting my first Kerdi over the (worst possible substrate), it went off quite well. I will say, that I think you would have to try pretty damn hard to get that hardibacker too wet. I literally sprayed a few gallons of water on it with a garden sprayer all morning long. It still never even really felt damp, although I know that it was. I used TEC uncoupling membrane mortar, and am quite confident that everything turned out well. Everything went on much smoother than I was expecting. I did it in stages...mixing about 1/3 bag of mortar each time and setting as many pre-cut sections and corner pieces as I felt I had time to.Six stages later, I should finish up the curb tomorrow and be done with Kerdi!

Was wondering if I can use some of my leftover Kerdi as an uncoupling membrane on the concrete floor in the rest of the bathroom?

03-05-2017, 08:38 PM
Kerdi is neither an uncoupling membrane nor a crack isolation membrane and is advertised by its manufacturer as a waterproofing membrane for shower applications.

I'd recommend you select another product for your bathroom floor, but it's your house, your floor, your Kerdi, and you can do whatever you think will work for you.

My opinion; worth price charged.

03-05-2017, 08:44 PM
Thanks CX... I probably will. Just have a good bit of Kerdi leftover and couldn't find any info about using it on a concrete floor...probably for the reasons you listed.

I actually tiled the adjoining bathroom about 10 years ago and didn't even know about such things. Tile still looks great without a single cracked grout line. Just lucky I suppose