Curbless shower with a PVC liner — how to terminate the liner at the floor?
I’m installing a curbless shower—-Concrete slab-on-grade with a sump for shower.
Using traditional method for shower floor—PVC liner, with pre-slope and top slope mud beds.
2×2 tile on shower floor and 18×18 travertine on bathroom floor.
My question is how to handle the waterproofing interface between my sump and the bathroom floor level (like where the curb would have been).
My plan was to have the PVC liner (.04″ thick) overhang the shower pan onto the bathroom floor about 4″ and then just tile over it. But that gives me elevation problems with the rest of the bathroom floor unless I attach travertine directly to the PVC liner with thinset (I’m assuming that’s not acceptable).
A hybrid option of that would be to use 2×2 mosaics (1/4″ thick) outside the shower sump area, and onto the bathroom floor for about 4″ to allow a thicker thinset bed over the 4″ of PVC liner on the floor. So I might end up with a 3/8″ thick mud bed to set tile over the liner–is that enough? What is the minimum? SEE ATTACHED SKETCH & ATTACHED PHOTO.
Another option is to cut off the liner even with the sump/floor interface. I like this one the least.
No matter which option I use, I have concerns of water leaking under the liner and flooding/saturating the shower pre-slope mud bed, defeating its entire purpose. Using a door inward from this interface would help, but I’m still concerned about water finding it’s way down the back of the liner. What could I use to seal the liner to the floor to avoid this (regardless of whether I cut the liner off at the sump lip or cut it 4″ out onto the floor)?
I would appreciate any comments.
GBA Detail Library
A collection of one thousand construction details organized by climate and house part
Replies
This is your BABY if you want it installed correct!
http://www.schluter.com/143.aspx
or Schluters newest competitor
http://www.trugardshower.com/
I should also add... thinset will not stick to PVC, not much does. Your described solution(s) will eventually leak since PVC membranes are designed with a curb.
As shown below, a curb is required for PVC liner use.
http://www.ipscorp.com/pdf/watertite/Watertite_ShowerPanLiner_InstallInst_Sep09.pdf
I'll be more than happy to help guide you through the correct procedures if you find yourself in a bind.. 860-739-5596 Richard Beyer / Pataya Flooring & Stone Supply
A fellow contractor uses Redguard and I am going to use it sometimes. I also use Schluter products. Sounds like Richard is in the business and could be a great help.
With Redguard we double cover bases and taped joints.
One thing I will not due is use drywall on the walls which many production builders do. Millions of homes done with drywall, lots of work for us in redoing such, thanks for the work!
Hi AJ!
I agree with you on the drywall aspect, because RedGuard is vapor permeable! Many tile tradesmen and builders think it's waterproofing. It's not! It's water resistant.
I personally tested several manufacturer's liquid applied systems inside cardboard boxes with their patented fiber tape at all change of plains. After 72 hours of curing time I filled the cardboard boxes and left them to stand for weeks until mosquito's moved in.
They all passed the standing water test with a 3 coat application of their liquid applied product. 2 coats, yes they leaked. One thing that tipped me off to water resistant is the fact the products change color when wet. Latex House Paint does not.... Hmmm
These products are not designed for steam shower's either, they will fail.
They will not stick to concrete if you can rub the concrete and sand particles show up on your hand. I also found when concrete is treated with rapid drying chemicals, specially formulated plasticizers (C-21), a chemical reaction occurs causing blisters and debonding of the liquid applied system.
Also, liquid applied systems rely on the old traditional mud pan system which complicates the sealing process at the drain leading to failure. ie; unless you modify a Schluter or TruGuard drain which I do not recommend.
Back to sheet applied.....
Cement Board or HardiBoard is best for the walls. Do not install sheet membranes without first taping all seams and corners and be sure they are filled and smoothed out. Do not use to much thinset or this will build out your taped seams. ie; your tile will look like a bicycle ramp after it's grouted if you rely on the flatness of the wall to gauge your tile surface. I see this alot at the floor line and inside corners.
For this application there's only one of two ways I would attempt this project. For a DIY situation, sheet membranes are best. Just follow the manufacturers directions! Option 2 requires skill and training and this includes RedGuard. I'm not going there for this post. The key to any professional waterproofing job like this project is proper flashing (seal all change in plains), surface preparation and using the proper mortars at the proper depths. Yes mortars! Not all are created equally and not all can be used under porcelain tile or natural stone. I do not recommend MASTIC inside of your shower or under porcelain tile! Take your time, allow products to properly dry and follow directions!
Now my jab at those tight builders out there who are profiting from the sweat of another man.
There are plenty of $4.00 per square foot installers out there who are more than glad to hack up your customers shower and there are some great guys to who work cheap. They are simply poor businessmen.
The really good guys charge upwards of $25 to $75 per square foot to build a perfect shower. Why is this you may ask? Because time is money and taxes have to be paid. Walls are almost NEVER plumb and flat which means more time to straighten them out. No good tradesman can pay his taxes and follow the law on $300.00 to $400.00 per 8 hour shift with a helper. He may as well flip burgers or bag groceries. I brought this in for conversation because good tradesmen and women are not valued like in past days. Sad when the finished product is what you see every day you walk into your custom bath or kitchen. Tile is not fool proof and requires tremendous skill and years of experience to be installed correctly and permanently.
Richard, since this thread has some great advice, please outline best practice for sealing tile walls to porcelain tubs. I silicone the board to the tub before tiling.
Thanks for the tip to three coat with Redguard, I will pass that tip along.
AJ,
The backer board should stop just above the tub lip. Sealing between these two junctures with 100% silicone allows the tub to move independent from the tiled wall. The tile will then come down over the juncture and finish off at the tub deck. Caulk where the tile meets the tub deck. I prefer to set the tile on a 1/16" spacer keeping it off the tub so when I caulk the edge the caulk has something to hold onto other than a face seal, if you know what I mean.
Weep Holes---
I think you're going to need a couple of weep holes in the tile-to-tub silicone caulk joint.
I think the e-books available here:
http://floorelf.com/library
are pretty damn useful, guiding people through the whole thing with a sense of humor (he includes traditional PVC liners, liquid applied, and sheet membranes. FWIW (and that ain't much), I'd look at the Laticrete membranes: http://laticrete.com/homeowners/products/waterproofing_anti-fracture.aspx
It's a shame that FloorElf's question and answer sections are a mess (all the questions on all topics pile into the comment thread on the articles on blogs).
One not-quite-well-known enough aspect of using the sheet membranes is that if you do it over concrete board, the concrete board sucks the water out of the thinset at a tremendous rate. The solution (if you don't want to use drywall under it) is to seal the concrete board with a primer like that used for self-leveling compound.
John Walls... Weep holes are required around a conventional mortar bed drain, not in a watertight joint along a tub deck. Personally I've never seen or heard of your claim for weep holes in silicone joints and I've never read anything like this before in the technical literature published by Tile Council of North America (TCNA) or Marble Institute of America (MIA). If you have some literature I'm missing please post it here. Weep holes are also specified in exterior brick and mortar assemblies.
James said; "concrete board sucks the water out of the thinset at a tremendous rate"
I disagree with this statement for the following reason. Not when you mix the mortar in accordance with the sheet membrane manufacturer's directions and work at a professional rate of speed. Sheet membranes require the mortar to be mixed at a thinner consistency than mortar you would mix to install tile. If you install at novice speed the mortar will dry out requiring you to remove the mortar and start over. One way to avoid this issue if your experiencing it is to pre-cut all of your sheets before mixing the mortar. I agree about Laticrete's system. Laticrete has been around for a very long time and they do make good products.
Personally I'm biased toward Mapei for technical support and Ardex for superior self drying mortars. Ardex manufacturer's in my opinion the BEST roll on waterproofing systems in America. I say this with experience because I have tested and used almost everything out there.
ARDEX 8+9... http://www.ardexamericas.com/en-us/Products/tilestone/Pages/8-9.aspx
You better know what your doing when you work with this product. It sticks to absolutely everything and it's not washing out of your clothes so protective equipment is mandatory. Oh and forget about reusing tools after using this product unless you have a helper standing close by continuously washing your tools! ;) Also, it's definitely not as user friendly as all the previous products listed in this blog.
ARDEX does offer free training at their facility in PA if a plane ticket is affordable to you. Well worth attending if you are in the business of doing things right the first time.
Weep holes----
The caulk joint is indeed water tight. If you don't have weep holes (tile-to-tub), where does the water go that gets past the tile and grout (in the field of the walls) from the deluge of the shower head? Does it just collect behind the tile and stay there, or maybe slowly seep out the grout above the tub lip?
No, I don't have a code to quote--just trying to understand the logic.
John,
I think your mistaking STEAM shower (forces water vapor into the grout) issues versus REGULAR everyday shower usage (water runs down the grout and into the tub). With proper bathroom ventilation both scenario's dry out rather quickly.
In both scenario's when a sheet membrane is used behind the tile water and vapor drive have nowhere to go but back out from where it came from. That is when the system is properly installed.
The key to mold and water problem prevention is mechanical ventilation. How many times have you entered a friends bathroom or stayed in a hotel to only see dew striping on the walls and mold all over the shower or in the corners? Pretty nasty, right? It's not always house keeping as much as it is poor exhaust ventilation. I would be more concerned with your bathroom ventilation than where the water is not going when the job is installed correctly.
Richard, I build high end bathrooms every winter. your posts are priceless and highly appreciated!
One of my biggest pet peeves is how terrible tile work is done. I get to redo at least one failing tiled shower a year. Thanks for the work those of you that stick tile to drywall with mastic. You guys are money in the bank.
Thank you AJ...
I NEVER ever recommend mastic. I'm baffled at why some contractors use it. What's so difficult about mixing thinset mortar correctly? The best craftsmen I know only use epoxy and high end thinset. Mastic is left for the DIY community who do not know any better. Also, Mastic in many cases costs a premium for a temporary bond. It simply does not make any sense to me.
Richard, thanks for your comments. I have a few followup comments and questions, please.
1) My reason for wanting to go with a traditional PVC floor liner was because I thought it would require less training, and thus be less prone to error than a sheet applied system such as Kerdi.
2) My goal was to have a curbless shower, thus the sump in the foundation slab.
3) Apparently your opinion is that having a curbless shower totally rules out the use of a traditional PVC lined floor. So, if I want a curbless shower, I need to go with a topical membrane system floor of some kind--correct?
4 ) Regarding Redgard (or Hydorban or other painted-on membranes), you are saying it won't stick to a mud bed, so I must go to a sheet applied membrane system---right? And Redgard is not waterproof anyway?---right?
5) Regarding the use of Redgard----2 coats is not waterproof, but 3 coats is waterproof? Is there a dry film thickness associated with the number of coats you tested? I've never used Redgard, so I don't have a feel for it, but I know that paint can be applied in thick or thin coats.
6) Should Redgard or Hydorban not be used on a shower floor or walls at all? If I want to use a topical system, am I limited to a sheet applied system of some type (like Kerdi)?
7) In your mind, is there any way I can take advantage of my sump and still use a PVC liner? How about if I had a step-down into the shower floor (about an inch or so) ---would that work? Not exactly a traditional curb, but a hybrid of sorts.
8) Does Ardex stick to PVC?
9) If I have misapplied or misunderstood any of your thoughts, please straighten me out.
Richard, regarding the weep holes in the caulk at the tile-to-tub joint discussed previously-------
See Peter Yost's blog "Backerboards-Winners against Water" on this GBA website. He doesn't like using any caulk at all at that point---citing personal experience with failure at that point due to the caulk holding moisture (see drawing and comments #25 & #26 on that blog).
So, unless I have misinterpreted something here, you two are diametrically opposed on the subject, and I'm stuck here in the middle with weep holes. What could it hurt to have a couple of weep holes? Best of both worlds?
John....
Peter apparently has not experienced a properly constructed "waterproof" Shower. In his description from the link you refer to he's using a vapor permeable roll on membrane. He still needs to caulk all change in plains to prevent water damage because materials expand and contract and those products are not waterproof unless applied to a 30 mil thickness as tested.
http://www.custombuildingproducts.com/media/59911211/tb63_redgard_steam__shower.pdf
A shower is not a facade on a building. Rain drive can not be compared to an enclosed heated shower with vapor drive.
If you want weep holes, use them. Your argument should be between you and your wife depending on who cleans your shower. Then explain why you have dental tools in your cleaning supplies to dig out the soap scum and other great finds usually associated with used shower assemblies. Once again, your not building a brick facade.
When caulk and tile are properly installed there should be minimal caulk to be seen. (+/-1/8")
Roll on membrane's are water vapor permeable. They are NOT WATERPROOF unless applied to a 30 mil thickness or as tested by the manufacturer. This means more than 2 coats must be applied.
"failure at that point due to the caulk holding moisture"
If Peter is treating his shower tub surround like like a steam shower and it's not built to steam shower standards.... that's what happens.
If he's not ventilating the shower correctly after use... that's what happens.
If he leaves standing water inside his shower... that's what happens.
If he leaves his shower door closed after use before it dries out... that's what happens.
If he refuses to use a squeegee after showering... that's what happens.
VENTILATION and MAINTENANCE is the key to any successful shower/tub build. Leaving a gap between the tile and tub only allows for much larger problem's in my opinion.
If you want a caulk free shower it can be had without the mess by using Schluter DILEX-EKE tracks...
See: http://www.schluter.com/6436.aspx
John,
I made a correction to my comment above. I located a RedGuard Tech bulletin which I was unaware of. They claim when their product is installed to 30 mil it passes the ASTM standard for a steam shower. My apology.
http://www.custombuildingproducts.com/media/59911211/tb63_redgard_steam__shower.pdf
I do know is this is not possible in 2 coats and 3 is really pushing it to achieve 30 dry mils. Your only means of knowing if you met this standard is by requesting a mil gauge from a representative in your area to measure with and also a concrete roughness scale before using the product over concrete or mortar. These come with a fee. Yes, there is a standard for the roughness of the concrete when using roll on systems.
To answer your previous questions....
#1.... Sheet applied systems... you really need to try to screw them up -v- traditional pans which require extensive training to complete them to published TCNA standards. I see many of them leak and I never have seen one in my region installed correctly which is why they leak. I have also seen the Oatey 60 mil pan membrane crack like peanut brittle after 15 years of sitting under a mortar pan.
#2... You can still achieve a curbless shower with sheet membranes like Schluter.
#3... Correct
#4... The chance of a bond failure is extremely high for a novice installation. These products are not fool proof as much as marketing implies. Sheet membranes (Schluter) are to easy to not use them and your risks associated with meeting the dry mil thickness is eliminated with gauged sheet applied systems. I retract my comment about Redguard not being waterproof because technically according to Redguard literature I recently found they are when installed to a dry mil layer of 30 mil. 2 coat applications are not waterproof.
#5... See... http://www.custombuildingproducts.com/media/59911211/tb63_redgard_steam__shower.pdf
#6... I do not recommend a novice to use roll on systems at all. There's to much room for failure and as the saying in insurance goes... "Your not covered...Installation Error.... Does not meet the manufacturer's specification"... If that's not a good enough explanation to stay away, it's buyer assumes all liability and your performing at your own risk.
These roll on systems require preparation techniques and training beyond the novice skill level. Even "experts" have failures in the millions of dollars with roll on systems. They are not fool proof.
#7... I do not recommend it. To risky.
#8... Do not try it. It's not recommended or warranted by Ardex.
#9... I suggest that you attend a Schluter workshop in your area before proceeding. They are usually one or two day FREE seminars. Stay away from roll on systems unless your absolutely confident you can follow directions to the T and your confident that if you do have a leak your homeowners policy will not have an escape clause. Get everything in writing from the manufacturer of choice and a written warranty with instructions on how to achieve their warranted results. Regardless of what you decide get trained or hire a tile contractor who has been trained by your manufacturer of choice.
Richard, I have repaired many a tile shower tub mated on drywall. Done any way better and no repairs do far for four decades.
Still, am a fan of your advice on this thread anyhow.
Aj (PEX and redguard and Schluter lover)
Quote: "1) My reason for wanting to go with a traditional PVC floor liner was because I thought it would require less training, and thus be less prone to error than a sheet applied system such as Kerdi."
The Kerdi system is the most foolproof. I built (my first) one, also on a slab, 10 years ago in a rental and it looks as good today as it did then. I've built 5 more since then.
Nice job Jeff! Good to hear from someone who believes in the benefits of this system as I do.
OK, Richard, I'm convinced that I should use a Schluter Kerdi sheet membrane for my curbless shower floor. Where do I stop the membrane? Do I lap it out onto the slab also? How far? 4" maybe?
Please click on the pdf file at the top of my picture at the beginning of this post to see my originally suggested profile. Ignore the PVC liner on the sketch and assume that Schluter is installed just under the tile thinset. I would appreciate your comments on this layout. Is it more complicated than necessary? Should I just go from sloped shower floor-to-horizontal bathroom floor at the sump-to-slab intersection?
Jeff, your shower has a curb. Tell me about curbless designs.
John,
If I were building your shower, (for a nominal fee of course) I would bring the Kerdi membrane outside of the shower past the potential water line by 2 inches. Install Schluter Ditra onto the adjoining floor (outside of shower floor). Using Kerdi band overlap the junction between the Ditra and Kerdi and all seams (Ditra and Kerdi). This makes for a water tight system. At all change in planes overlap all seams with Kerdi Band. This includes the first 4 feet along the walls outside of the shower to prevent water seepage from riding up the drywall which made it out onto your adjoining floor.
Rule is 2 inches of over lap is plenty to each side of a seam. I prefer the overkill scenario which is why I use the wider tape rather than the minimum acceptable 2" practice.
When installed correctly your water tight. Anytime you use sheet membranes you must follow the tested procedure recommended by the manufacturer. Schluter has your question in a published publication for curbless showers. What your building is nothing new to the tile industry. If your not successful in locating the document call Schluters technical department directly as procedures and recommendations do change from time to time.
Like I said previously, get it in writing from the manufacturer! That's my opinion.
John, I'm getting ready to do my own bathroom remodel using a curbless shower design. I've found there is tremendous in depth information on Youtube if you just type in Schluter. It tells you exactly how to do it.
My understanding is that there are two ways to go. If there is a lot of room in the bathroom then they make a ramp that can be placed in front of the shower. That is the inelegant way to go...
The second way is to have the floor of the bathroom level with the shower entrance. Here you build the shower so that the finished level of the shower base, including Kerdi, meets the finished level of bathroom floor, including Ditra uncoupling membrane. There are two approaches here. The first is to lower the shower area, usually by cutting back the floor joist an inch and a half and sistering them with new joists. This will lower the shower, including the base so that it meets the existing floor in the rest of the bathroom. That is the elegant solution. The second way is to build up the entire bathroom floor an inch and a half so that it meets the level of the shower base. This isn't as good because it means there will be an inch and a half rise between the house and the bathroom.
If you have decided on Schluter then it is time to do your own homework. The inch and half is just a rough approximation. If you watch the youtube videos you will get a much better understanding of what is involved. I haven't done it before either and they are what I'm using. I'm pretty confident that I can do it using them and the excellent supplemental info I get here.
Eric,
Be careful of Youtube. Most of those video's are DIY contractors who have not received any training. I know Schluter has published tutorials and I know Bryant Bouchard who is in most of those Schluter tutorials. He was the man who introduced me to Schluters product line back in 2001 and he along with David Gobis (former TCNA technical expert) along with a few other men, trained me to use their systems at the Tile Council of North America headquarters in Clemson South Carolina back in 2002.
John's shower is already constructed for a perfect world scenario. Take a look at his rough in photo above.
Next... A ramp in front of a shower is essentially a curb and is made from foam. If your remodeling and your limited in joist height this may be a solution for you without extensive expense and renovation deconstruction. Good for wheel chair accessibility otherwise it looks like a poorly designed curb.
You said; "There are two approaches here. The first is to lower the shower area, usually by cutting back the floor joist an inch and a half and sistering them with new joists."
This could also be a code violation.
Richard, I only use the Schluter published tutorials.
I guess I should add that I'm doing a gut job on my bathroom so that influence may have crept into my comment for John. I plan on cutting back the floor joists in my shower area. I can assure you that I won't skimp on the support because I will be adding lumber that is itself supported by beams to the existing cut down original joists. I know how to do that though others may not. I still think that is THE elegant solution but agree that it may not be appropriate to the scope John is working with.
Any chance of reviving this thread?
I'm getting a curbless shower built in a powder room remodel and while checking into the methods have come to understand that a topical membrane, whether Kerdi or hydroban or others- right under the tile- is the best and possibly the only acceptable practice when there is no curb.
OK, so I had a great tile company recommended to me very respected, lifetime warranty on work, owner is a great guy to deal with, very experienced with his crews doing several baths per week.. When I talked to him a few weeks back he assured me that he uses hydroban. Now, as we are getting ready to go, he's clarifying that he will put a pvc liner in under the mortar bed clamped into a drain - the usual curbed technique- ending it some inches beyond the edge of the curbless, doorless shower area.
Then he will use hydroban on top of the mortar bed, running it over the whole floor and up the walls as far as any baseboard tile, if used. I'm not clear on how he will terminate the hydroban layer at the strainer, or maybe up at the linear drain, I think.
I commented that this seems unusual and that the surface membrane should be the pan, not the pvc liner below, right? No., he says the hydroban is not the real pan, that the liner clamped in at the weep holes is.
Is this an acceptable practice? Anything to be concerned about?
Thanks,
Steve
Steve,
When you go with a membrane system your shower is as good as your installer. I have a great tiler, but I don't like trusting them with waterproofing details. I use pre-made shower pans instead. They put limits on the size of the shower, but they are fairly idiot-proof.
http://www.tileredi.com
Why both? Sounds wrong.
If the PVC liner is the pan, what function does the Hydroban serve?
Is the PVC liner on top of a sloped mud deck with another sloped mud deck on top of that (typical traditional set-up)? If not sloped, it won't drain, so what function does the PVC serve?
If his goal is to sandwich the mud bed between two liners, then your concern about how the two different systems terminate at the drain is valid. Even if it is successfully terminated you are subject to the dreaded mold sandwich. If not successfully terminated, I suspect you are guaranteed mold problems between the two liners..
I suggest you post your question on floorelf (google it) for some insight from a guy who does all types of systems..
By the way, I'm going with Kerdi topical configuration (with nothing under it but mud deck on top of concrete slab on grade foundation).
Yes John, that's what I'm understanding. I really want to use this company, but I'm concerned tabout combining two systems. And as Malcom says, the bonded membrane, especially a roll-on,. is only as good as the installer. I believe these guys are very good, just that if you are not taking the "bonded membrane" install seriously as the pan, then you may not make every effort to get full coverage and close it in, relying on the liner below to catch any filtration. Then a mold sandwich is more likely, even if leakage to surrounding areas is contained by the liner under the membrane.
Any tile pros with extensive curbless experience care to weigh in?
Thanks
I'm no professional at this but I'm also designing a barrier free shower. The easiest solution I've found is done using a Schluter LS drain. I'm not in any way associated with Schluter but their method using Kerdi and Ditra seems to be the gold standard in shower and bathroom waterproofing. There are other similarly effective systems out there but they are copying Schluter.
Here's a youtube video that I'm using as a template for my installation:
https://www.youtube.com/watch?v=5C1s3YNYnfc
The relevant part starts at 4:30 into it and the really specific part comes at 7:10. It does not require a ramp at all, nor does it require one to sink the shower base to make up for that. I've already ordered the shower LS base and I've measured it, with the drain on top of it at 1" thick approximately. One then has to build up the floor (without tile) to match that 1". This requires 3/4" thick plywood and 5/16" thick Ditra XL. The Ditra XL is generally used when you have to match tile thicknesses of 3/8" to 1/2" to 3/4" thick real hardwood floor. This works for me since I have 3/4" thick hardwood floors elsewhere in my house. It may not work for your situation.
But overall I agree with Malcolm's assessment. Look at as many Schluter sponsored shower system videos as you can to see how they waterproof showers. It's the gold standard. Do that waterproofing yourself using their system and a shower tray designed for it and you will have no problems. Then get a good tile guy to do the tiling. No sense doing something like that yourself unless you enjoy it. (I don't)
I guess I should correct one thing I said about not having to lower the shower base with a Schluter LS line drain. My house happens to have diagonal planking that I have placed 3/4" thick plywood (actually 11/16") over throughout the house to increase rigidity. I did NOT put plywood over the planking in the shower area. So that would be the same a lowering the shower area by 11/16". The 1" thick LS shower base then went over it. This ended up being a very accurate system fit but it probably wouldn't work for a typical house. For me it is the most elegant way to create a barrier free shower because there really should be almost no visible transition between the shower floor tile and the rest of the bathroom floor tile. If you can make it work for you and your house then it seems like the way to go.
Edit: You can also make the bathroom/adjoining room transition acceptable to a thinner flooring material than 3/4" hardwood, say 1/2" or 3/8" thick tile or manufactured wood floors. To do this you would lower the shower area before the LS base install to 7/8" below the rest of the untiled bathroom floor area. One would then use regular Ditra over the bathroom floor instead of Ditra XL. Regular Ditra is 1/8" thick vs 5/16" thick for Ditra ultra. The negative 7/8" thickness plus the 1" thick tray equals plus 1/8" above the surface of the rest of the untiled bathroom floor. One then uses regular Ditra, which is 1/8" thick, on the bathroom side to make them equal. That is the important transition required to to be even to make that tiled transition area invisible. The 1/8" thick regular Ditra also lowers the entire bathroom floor so that it is more acceptable to work with a thinner flooring material in the rest of the house. That transition doesn't have to be exact.
These are all ideas for people trying to get a barrier free shower that really looks unobtrusive. I did a late edit to correct a math error and to better explain how to even the two sides of that transition so they are even. My math apparently sucks. These are not necessarily ideas for people that originally asked the questions here because they might be too far in the process for this to now work. More, it's for a fresh sheet of plans.
I understand that Wedi is also gold standard. Have use it as substrate in tub surrounds, pland to use Wedi shower kit with curb. Any feedback on Wedi Appeciated.