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otrex 01-30-2019 11:57 PM

Help Designing a Shower Floor
(posting here based upon advice from another forum)

Hello everyone,

My first time on this forum, and it seems there are a few people who may be able to help me with a shower I am designing.

I live in a 1940s house and it has a tiny bathroom (4.5' x 9') with the door on the short side and a bath/shower at the far end. Recently this shower has started to get a bit old and some tile is starting to look pretty shabby and so we are updating it.

Complicating the situation is that someone about 30 years ago cut a large U-shape into one of the floor joist to allow the toilet drain to pass through, and then didn't bother to buttress that spot, meaning the floor has sunk quite noticeably there over time. When we bought the house the first thing I did was to put a couple of jack posts under this spot. I cannot push the house back up very far, but I did halt the sinking.

I should note here that underneath this shower is the crawl-space which features dirt. So fortunately any leaks downward from our current shower are not ruining any space below.

For the shower, we want it to be a curbless walk-in shower with the same porcelain tile all the way through to maximize the visual size of the space. We're adding clarity 10 glass to divide the shower from the rest of the bathroom, but there is no curb or other solid distraction to make the bathroom smaller (currently the shower curtain, when closed, makes the bathroom look like a phone booth).

All the options for structure are clear to me - we are remaking the entire shower area with Kerdi Board - with one exception - the shower floor.

I have been reading online about the importance on a reasonable slope and the reno provides an interesting opportunity. I am cutting the entire subfloor out right down to the joists and then will sister new joists onto the existing ones. In fact, whereas the old joist are 2x8 , I plan on using 2x10 for the sistered ones in order to allow me to make the above subfloor nice and level again. However, in the shower area, I plan on using a 48" linear drain along the back short wall, and then tilting the shower floor in that direction, meaning I don't need to have multiple angles to the drain - just one slope will ensure all the water goes to the drain. This is also important because I am using tile which is 6" x 3 feet, so I'll simply place these perpendicular to the joist and then having only one slope means this large format tile can be used.

Because of this desired setup, I am simply going to have that portion of the subfloor tilt using the new joist at between 1/4" and 1/2" per foot. Since the shower is no more than 3' wide (if that) this makes for a very low total drop from the highest spot to the lowest.

Now, keep in mind that I wanted this to be a curbless walk-in shower, so this presents a problem. If I follow the traditional 2-3" dry pack mortar plus liner etc setup I end up having a shower pan thicker than the floor outside the shower meaning a step up to get into the shower.

Therefore, I am wondering a couple of things:

i) If I am making the correct slope in the subfloor, can I avoid the mud bed completely? I need to note here that in addition to the new floor joist I will also be building much more substantial support for all the joist to reduce any bouncing.

ii) If I do skip the mud bed, I am thinking of having the subfloor made from 5/8s plywood which is then thinset and then 1/2" cement board applied (with mesh in between for strength/grab). I should note here that my joist are on 16" centers, hence the selection of 5/8ths. I would go with 3/4" if it was wider than that or if I was using a lot of heavy dry-pack mortar, but this proposed setup, I think, will be quite a bit lighter.

Then, in order to have a decoupling substrate for the large-format tile (so it doesn't crack) I would then mortar Ditra on top (since I'm using it everywhere else on the bathroom floor). I have spoken with Schluter and they say Ditra should not be directly-tiled in this manner, and so I propose properly thinset mortaring the Ditra as if I was getting ready to tile, but then applying Kerdi for a nice smooth (if not a bit redundant) finish). Then I would tile on top of the Kerdi as per normal Kerdi procedure.

The goal is to allow for a nice stiff floor but also to have the decoupling advantage that Ditra offers as a substrate (since their normal styrofoam pans are not available in the size I would need). From there it's just a matter of ensuring all the Kerdi is properly sealed to the edges/drain/Kerdi Board walls.

Does anyone see a problem with constructing the "shower pan" this way. Is there anything I can delete from the pan layers?

iii) If this doesn't work, how does one build a completely threshold-free shower without having a shower subfloor portion which is substantially lower than the floor next to it?

I realize that this is not standard shower pan procedure, and I have read a lot in the last few days. However, I am hoping that this still presents a valid way to maintain waterproofing while still keeping the large format tile from cracking.

In any case, I will appreciate any feedback you can provide, and am happy to answer any questions if I have left something out.

cx 01-31-2019 10:53 AM

Welcome, Kevin. :)

Originally Posted by Kevin
When we bought the house the first thing I did was to put a couple of jack posts under this spot. I cannot push the house back up very far, but I did halt the sinking.

Since you have jack posts under there I would recommend you give'em a quarter turn every few days until you've got the joists reasonably close to where they should be. Like with planting trees, the best time to do this was 20 years ago. Second best time is today.

When you sister in your new joists, you want to make the tops in plane to a very close tolerance. Your large format tiles don't give a rat's patooti whether the floor is level, but they care a great deal about flat. The tile industry standard is no deviation from intended plane of more than 1/8th" in ten feet nor 1/16th" in any two feet. That's a very, very flat floor and you'll be glad to have it come time to set those long tiles.

Originally Posted by Kevin
I plan on using a 48" linear drain along the back short wall,..

Perhaps you could post a drawing of your plan? From your description I would have presumed the back wall of your shower to be the longest wall with two shorter walls at each end and your glass wall/door parallel to the back wall.

Perhaps I'm not understanding the dilemma with the floor. Actually, I'm sure I'm not understanding. You plan to put the drain against and parallel to the back wall of the shower? That would have the shower floor slope down from the entry to the back wall? Let's find out if that's the plan before I go any further.

In any case, I would recommend you drop the entire shower footprint sufficiently to make a sloped floor of deck mud from a height allowing you to match the bathroom floor height and sloping to your drain. That would allow you to exactly match heights with only your Kerdi on the shower floor lapping over the edge of the Ditra on your bathroom floor. Not sure why you're concerned with the weight of a deck mud substrate, but it's a non-issue. If your floor structure won't support the necessary mud, you've got another, more serious issue.

For subflooring I would recommend nothing less than nominal 3/4" plywood. Your suggested 5/8ths" plywood is the absolute minimum recommended by any substrate manufacturer. I would personally not consider tiling over such a single layer subfloor under any circumstance. As for the 1/2" CBU, all manufacturers of such products recommend their thinner panels, usually 1/4", for floor tiling. There is no advantage to the thicker CBU unless you simply want to raise the height of your tile installation.

And I'm not sure where the CBU fits into your plan if you have planned to use Ditra as your substrate on the bathroom floor.

I'll stop there 'till we get some clarification on the plan.

My opinion; worth price charged.

otrex 02-01-2019 03:40 AM

1 Attachment(s)
Thank you for your response. Yes, I can certainly shed a bit more light on this build.

For the jack posts and floor, I don't see any reasonable way to get the floor back to its original level without seriously damaging the drywall and other rooms above. It's a 1 1/2 story with two bathrooms (this is one of them) right on top of the most sagged part, and while I would say the drop is no more than about 4" in the worst part, every time I turn the jack posts you hear quite a bit more cracking and substantially more resistance. To complicate matters, some of the upstairs bathroom was built/tiled taking that sag into account, so the more I push the greater chance of having to reno another bathroom. It is still improved from when we bought the house, but I suspect I'll have to cease pushing up very soon and just correct the subfloor as I reno each room.

Regarding the bathroom layout, I'm attaching a really lame sketch of the current and planned layout.

Yes, the plan is to have the drain at the back wall, perpendicular to the spray of the shower head and opposite the main door to the bathroom. The main reason for this is that the 6" x 3' tile will run across the floor relative to the main door (across the short span, matching the direction of the planks throughout the house).

What this means for the tile is at the point where the shower glass splits the room into two portions, this is the point at which I would start sloping the subfloor. That means about a 3' wide shower with 1/4" - 1/2" of slope to the back wall where the linear drain picks up the water (I realize now I'm going to need the drain to run wall-to-wall).

Yes, the CBU was simply to add some depth to the custom shower pan so as to allow the linear drain to have a proper height which to meet the kerdi. I had not planned on using it outside the shower on the bathroom floor since, as you noted, Ditra would be there.

Something I had not considered would be cutting the subfloor (as before) and then taking 2-3" off the joist in the shower pan area all the way to the wall and then buttressing this all with new sistered joist and posts. Is that the traditional way to create a curbless walk-in shower? If I recall from my framing days, such stripping of the joist can only be about 1/3 the way through before it weakens it too much, so on a true 2"x8", I could take 2.75" away at most.

Rather than the weight, my only concern there is that even with the minimum of 3/4" of slope across the 3' wide shower, the highest part of the slope would only leave 1.25 - 2.25" total for the dry pack mortar bed and Kerdi, which in my reading seems a bit thin, right? That's what led me to the idea of using the plywood, CBU, Ditra, Kerdi "stack" to simulate a shower pan in a space that's a little too shallow for dry pack mortar. Of course, I would prefer the traditional installation method if there was a way to do it.

Speaking of a more traditional method, am I correct that this would simply be (from bottom to top) 3/4" plywood, 4mm poly, dry pack mortar (2-3"), thinset, kerdi, thinset, tile? Or am I missing something there? That compares to my revised plan in the shower area (not the bathroom, just the shower) of: Plywood, thinset, CBU, thinset, Ditra, thinset, kerdi, thinset, tile.

Also, this raises the question: Is it the dry pack mortar that acts as the uncoupling substrate in the shower pan? What keeps the tile from cracking in the shower if something moves/shifts? I do like Ditra for that kind of protection, but unless dry pack acts as an uncoupler, I am not understanding how the in-shower large-format tile would be able to resist cracking as a house moves/settles. Once again, combined with the lack of height for a traditional mortar bed, that ability to absorb shifting was what led me to Ditra in the shower pan, considering I am already planning on using it for the nearby bathroom floor.

Noted on your advice to use 3/4 plywood. I will plan to amend that portion just to be extra safe and avoid movement (and also I understand I should put lots of drywall screws into it too, especially since I'm using large format tile).

In any case, I hope this helps explain the layout a bit better. I really appreciate your feedback thus far.

cx 02-01-2019 11:26 AM


Originally Posted by Kevin
Speaking of a more traditional method, am I correct that this would simply be (from bottom to top) 3/4" plywood, 4mm poly, dry pack mortar (2-3"), thinset, kerdi, thinset, tile?

Mostly. You would also fasten 2.5lb. expanded metal lath over your poly before placing your mud. The thickness of the mud would be from a minimum of 3/4" at the drain to whatever the required slope brings it at the perimeter. The big advantage to using deck mud in your application is being able to exactly match your necessary thickness at the drain and also match your bathroom floor height.

You might wanna consider a small curb or at least a bit of a hump at the door, which will need to open into the bathroom rather than into the shower. You can make it swing both ways if you want, but it's required at least to open out of the shower and the sweep on the bottom of the glass door will wanna drag on the floor if you don't make allowance for it.

Originally Posted by Kevin
That compares to my revised plan in the shower area (not the bathroom, just the shower) of: Plywood, thinset, CBU, thinset, Ditra, thinset, kerdi, thinset, tile.

Part of the problem with that, aside from not being able to adjust to the exact height of your drain, is that ANSI standards still, to the best of my knowledge, prohibit the use of CBU as a substrate in an application where the floor slopes to a drain. You might argue that they mean a centered drain and not a linear drain, but that's what it says. Schluter might also balk at that application of Ditra over a CBU, just because they have no specification for such. Not saying any of it won't work, just pointing out that you're wandering into a bit of a wilderness area.

Originally Posted by Kevin
Is it the dry pack mortar that acts as the uncoupling substrate in the shower pan? What keeps the tile from cracking in the shower if something moves/shifts? I do like Ditra for that kind of protection, but unless dry pack acts as an uncoupler, I am not understanding how the in-shower large-format tile would be able to resist cracking as a house moves/settles.

Yes,the mortar bed would be your "uncoupling" medium in that application. Keep in mind that the ceramic tile industry has no definition nor performance criteria for anything called an "uncoupling membrane." None. And when you talk about a membrane designed to prevent cracking of your tile installation with horizontal movement of the substrate, you're talking about a Crack Isolation Membrane, for which the industry does have standards. Ditra is not advertised by the manufacturer as a crack isolation membrane. And if your described "settling" involves vertical displacement in the substrate, you're on your own as far as any tile installation product manufacturer is concerned. KMAGYOYO as it were.

As for ripping down your joists to accommodate your proposed shower receptor, you simply can't legally do that unless you somehow support the ripped area independent of the rest of the joist structure. You could do that with your sistering if you were to install your sisters such that the tops aligned vertically with the bottom of your rips of if, as I think you're suggesting, you provide a new support under the ripped portion. Neither would provide any leveling or flattening of the joist tops, of course, and you'd still need to deal with that independently if you want it done.

Four inches, by the way, is what I'd consider a moderately huge bit of "settling" and I'd want to consider some serious repair. You're suggesting that some portion of the bathroom floor you're working on is actually four inches lower than other portions?

My opinion; worth price charged.

otrex 02-01-2019 01:21 PM

Thank you, once again, for your response.

Okay, I thought a mud deck needed at least 2" of thickness, but if it's actually 3/4", that does help.

Apologies, when I said "4 inches of sag" in the current house, I was actually meaning "4cm". That equates to about 1.58 inches. Still not great, but not as bad as 4 inches!

In regards to the transition at the shower door, yes, I am intent upon installing a special profile made by Schulter which is called Showerprofile-WS, essentially a semi-circular rubber and metal bump on the floor which takes the place of a sweeper on the door. This will be further complemented by the installation of Schluter DECO-SG alongside, which is basically a profile which accepts 10mm glass installations. This is to avoid having to use hardware for mounting the glass since the goal is to make the bathroom look bigger by having it as open as possible.

In regards to ripping down the joist, yes, I would assume that there would have to be a sistered "deck" of sorts created in conjunction where full 2x8 extend below the old joist and are then buttressed using a beam and posts for support. In this case that would serve two purposes - both a sturdy support for the weakened joist, but also a way to avoid further sagging of the subfloor. Of course, this new structure would ideally be flush to the top of the now ripped joist.

May I ask, other than ripping the joists down, is there any way that you know of to properly accommodate a mud bed for a shower pan? Building up the bathroom floor is not an option for me because the house has lower ceilings (wartime construction). Currently the ceiling in the bathroom is 7'11", and so I would not want to give away too much more height, especially considering the shower area will have a 3-6" drop ceiling. I should also mention that I stand 6'6" tall, so the ceiling already feels close enough (I get nervous around ceiling fans!).

Finally, I should note that I plan on installing a 28" glass door. Any wider and it would threaten to hit the toilet or not be able to open the whole way. As for opening direction, unfortunately I am stuck with it only being able to open inwards as a full swing out will impact the towel rack located on the left wall (the only option for the towel rack since the main bathroom door also swings inward).

Once again, thank you for this feedback.

Raymond S 02-01-2019 04:29 PM

Perhaps you could consider towel hooks instead of racks. I would do that if the door had to swing out.

jadnashua 02-01-2019 05:38 PM

Code requires the door to a shower to be able to swing outwards which would allow access to someone who might have fell and need assistance in the shower. Could you accommodate a slider? Minimum opening by code is 24".

FWIW, industry does call for deck mud to be thicker when installed over a wooden subfloor, but many people have success when done thinner. In your case, since it would be at the inside edge near a wall where you wouldn't be as likely or able to walk.

cx 02-01-2019 07:08 PM

1 Attachment(s)
Dropping the floor is the only realistic way I can see to accommodate your shower receptor given your other requirements.

You could eliminate the Deco SG and get a cleaner look by simply installing your fixed glass in the tile installation. Like this:

Attachment 206772

I think the shower door width minimum is actually a clear unobstructed opening of at least 22 inches and your 28-inch plan is at least 4 inches larger than I think necessary.

I'll leave the swing of the door to you and your code compliance official. You might wanna plan not to prevail on that one.

My opinion; worth price charged.

otrex 02-02-2019 12:21 AM

CX, thank you - just to clarify, when you say "dropping the floor" you do mean ripping the joist as previously described, right? If so, I think I'm going to start with that plan and then modify if my contractor thinks it's going to be too dangerous/difficult/expensive etc.

For the door swing, not sure what the code is here in Ontario, Canada. I'll have to check. I don't mind it swinging out, but it's complicated by the fact that there is PVC beadboard and chair rail right up to the glass door. The chair rail could be beveled a bit, I suppose to allow for "emergency out-swing". I do not wish to have a slider as it has too much hardware and makes the bathroom look too small. Clarity 10 glass is great but only if it doesn't have hardware everywhere. In the current bath tub layout if you dare close the shower curtain you reduce the rest of the bathroom to a phone booth! So the new design calls for long lines into the shower as if the shower isn't even there (tileable drain, no glass hardware etc). Even the wall coverings continue unabated right into the shower (noting that they are waterproof - in case someone thought I was going to use MDF or something!). The premise is that your eye should forget that a shower is even present until you need to take one, thereby maximizing the visual space of the room.

For the Deco SG, I only tend to want to use that because of the size/weight of the glass going in. It is planned to be floor-to-ceiling, and I would be nervous if it was just tile and silicone holding it in place. I'll show your photo to the tile installer and the shower glass installer and see if they prefer that route.

As for the width of the door, yes, I might ultimately reduce it to 26", but I'm not wanting to go too much less than that just for comfort (again, having the towel rack on the left as the only valid spot means it eats up a little of the door when you "comfortably" walk around it.

This work starts around February 11th, so if anyone is interested I can probably post pics... maybe in exchange for a couple more questions as we go along. Though I have a contractor (my brother-in-law) involved some of the work and most of the planning falls onto my shoulders.

Thank you, everyone for your comments, and I'll be pleased to read more if you have other thoughts.

cx 02-02-2019 09:50 AM

1 Attachment(s)

Originally Posted by Kevin
For the Deco SG, I only tend to want to use that because of the size/weight of the glass going in. It is planned to be floor-to-ceiling, and I would be nervous if it was just tile and silicone holding it in place.

The tile and silicone is all that will be holding the Deco SG in place, too, Kevin.

The tile bonded with thinset mortar will have far, far more shear bond strength that your glass could ever apply without breaking, even though tempered glass is quite strong. And if you're wanting to go full ceiling height with your glass, installing it with only one side of the glass tiled will make that feasible. Gonna be difficult to do with a fixed channel on three sides. Like these:

Attachment 206775

Entirely up to you, of course.

otrex 02-03-2019 02:55 AM

CX, I understand what you're suggesting, and it creates a couple of questions:

i) First, if my floor tiles are running across the short distance of the room (perpendicular to the joist), when I get to the place where the shower glass should go, do I just leave a 10mm gap for the 10mm glass to slot in? That is to say, the bottom of the glass is held by the surrounding porcelain tile (and silicone, of course)? This gap would be matched in the door area immediately next to it with the Schluter floor profile meant to hold back water in the door space, so that should be nice and even all the way across the floor. I assume, like the walls, the porcelain floor tiles should be employed to hold the glass if I'm not using the track profile rather than just sitting the glass down onto the floor tile. Then, I just leave the last row of wall/ceiling tile until the glass is installed, and then complete the tiling with one layer on the bathroom side of the glass to lock it into place?

ii) On the fixed glass side wall and drop ceiling, if I leave the 10mm space there, as you suggest what do I do on the door side? For example, on the drop ceiling of the door side there is nothing to slot into the ceiling, in order for the tile to line up that would mean I'd need a 10mm grout line? That seems pretty massive. The same is true for the wall on the door side. Since the door hardware is screwed into place right through the tile there, that means no gap in the tile is necessary to install, but that would mean that tile doesn't line up well either, unless the huge grout line is also employed there. What is the standard solution for this? Is it simply to rip the tile on the fixed side down by the difference in the gap in order to make the grout line on the door side the normal size?

iii) Since the walls in the shower area are to be made from Kerdi board, if I employ your suggestion and simply leave a gap, will the orange of the Kerdi board show through the side of the shower glass? If so, how do you stop that from happening? Same question on the floor, though the glass will be right on top of the Kerdi band which covers the line between the Ditra bathroom floor and the mud pan, so I assume it would be orange too and I'm just curious if that's going to show through.

otrex 02-05-2019 12:01 AM

In addition to my above questions (post above this one), I had another come up today.

My floor tile will be the same throughout the bathroom and right into the shower. Its 6" x 3 foot porcelain which looks like reclaimed wood. I should note here that it is rectified tile.

After reading the big tiling thread here about gaps for grout, though I wanted a 1/16th gap initially, it seems like most here woud encourage me to use a 1/8th. Fair enough. But based on what I'm reading, you're not supposed to use sanded grout on rectified tile. Trouble is, I'm not sure unsanded grout for the floor of a shower is such a great idea based upon what I'm reading about possible contraction.

Is this a situation where I should use an epoxy-based grout? I know it's harder to clean but at least I can say that I plan on using a dark brown grout to match the surrounding "wood" floor.

Answers to this and the questions in the post above are greatly appreciated.

cx 02-05-2019 01:32 AM

i. Mmmm, after a couple readings I think that's a yes. I would not make the space for the glass the same width as the glass thickness, though. I leave the better part of a 1/8th" gap on each side, which is then filled with a color-matched sealant.

ii. Again, if I understand the question. I would simply not cut the ceiling tiles where there would not be fixed glass and just leave the normal grout joint that would have been on the rest of the ceiling if there were no glass installed.

iii. I've thought about that when I first did an installation over Kerdi, but found it's not a problem. I do not ever set the glass directly onto the Kerdi, but use clear spacers to support the glass and I think that helps. The ones I prefer are little round clear spacers about the size of small Tiddly Winks unless I nut need more of a gap under the glass to make it fit the rest of the installation. You want to make the measurements very, very carefully for your glass. You can get whatever style and thickness spacers you need from the glass supplier.

iiii. I would not recommend epoxy grout for your shower floor.

I have no idea why you would not use sanded grout with rectified tiles if you can get it into the grout joints.

The think the very narrow grout joints look good on the wood-look tiles, but you're gonna find it difficult to maintain those joints when setting your tiles unless your tile are very well rectified and you are well skilled at setting the tiles.

My opinion; worth price charged.

otrex 02-18-2019 11:04 AM

Just wanted to post an update along with a couple new questions.

As per advice here, I will be ripping my joists down to create the necessary depth for a proper mud bed. As noted above, I'll be sistering some new joist on to the ripped joist for strength, and then jackposting this new platform down to the ground to help reduce movement.


i) If my mud base creates the slope to the linear drain and then Kerdi is on top of that, I don't need the traditional extra layer of mud on top of that, correct? Just thinset the Kerdi and tile, right?

ii) For the Dry Pack Mud Base, I know a 5:1 ratio is appropriate (5 parts sand, 1 part Portland Cement). But is this ratio based upon volume? For a 40Kg bag of Quickcrete Portland Cement, what would be the appropriate amount of sand?

iii) The Schluter Linear Drain requires a dry pack thickness of 15/16" to meet flush with the drain body. If I have a 30" wide shower sloping 1/4" per foot, I come up with a total dry pack thickness of 1.6" . That would mean a 60" x 30" shower area with a minimum dry pack thickness of 15/16" and a maximum of 1.6". Is this thick enough to be sturdy? Cleary I will need to have the subfloor as solidly built as possible to avoid deflection.

iv) I'm noticing a couple different grades of Portland Cement, such as "10F" and "GU". Any particular type I should be using?

Thanks again, everyone. Should have photos soon as the subfloor is being ripped up at this very moment!

cx 02-18-2019 02:09 PM

i. Yes. The Kerdi is what is called in the industry a Direct Bonded Waterproofing Membrane. You bond your tile directly to it.

ii. You can measure it either way, but volume is generally a lot easier on the job site.

iii. Done correctly it should be.

iv. I got no eye-dee what 10F might mean, but GU (General Purpose) will be fine. What you really want is plain ol' Type I and most of the bagged Portland available in my area is marked "Type I or II" and is also just fine (the Type II has a moderate heat of hydration, about which you couldn't care less in your application).

It would be helpful for some questions if you'd put a geographic location into your User Profile.

My opinion; worth price charged.

otrex 02-18-2019 03:41 PM

Okay, I added my location (Toronto, CANADA).

Bit of a letdown today tearing up the subfloor. We discovered that the floor joist in this area is 2x4! True 2x4s, mind you, with various doubles running here and there, but nevertheless that's going to completely destroy the ability to do a dry pack base anywhere because the deflection is so high and the weight probably too great. Some of the main beams are true 2x6s but they are several feet away.

The contractor involved said he wanted time to think about what to do and so has departed for the day. The trouble is with only some of the 2x4s bearing out onto the foundation, I cannot simply notch out the 1.5" that I need even with sistered 2x8s attached (so the contractor states). Now there is a challenge to find out how to make this subfloor stable enough for a mud base of any kind, let alone tile and a curbless format.

I don't know if you can notch 2x8s so they sit on the rather wide foundation wall and then sister them (with added jackposts down to something solid on the dirt crawlspace floor).


otrex 02-18-2019 04:02 PM

2 Attachment(s)
Just wanted to follow up that last post with a diagram and a picture.

The diagram shows the joist position. Hopefully that all makes sense.

The photo shows the current demo state as well as the joist.

Solutions are welcomed!

cx 02-18-2019 06:51 PM

What you have for joists is suitable for a ceramic tile installation, Kevin. The support under your beams is what you need to be looking at.

I think you can find a way to make that work.

My opinion; worth price charged.

otrex 02-18-2019 08:39 PM

The only problem is, I think, that I cannot get the 1.5" ripped out of the joist, right? Not sure how to make a curbless shower if I cannot safely rip out the necessary depth from the joist in the shower area. The double 2x4, in particular, would be down to just 2" of material left in a double after ripping it - not much to sister a joist onto even if I did make that sistering joist 2x8.

cx 02-18-2019 08:44 PM


Originally Posted by Kevin
Okay, I added my location (Toronto, CANADA).

Thanks. It was obvious that we weren't speaking the same language. :)

I wouldn't think about cutting down what you've got now that you see it, Kevin. I'd look more toward removal and replacement of what's in the way. May require setting at least one additional support for that center beam among other things, but I don't see why you can't take out a lot of what's there and install what you really need.

My opinion; worth price charged.

otrex 02-18-2019 11:06 PM

Thanks for your reply.

I am trying to see if I can replace that one double 2x4 beam and all the little singles with 2x8 joist running North/South and bridging in between, then rip those down by the amount needed.

The only thing I can think of that might accomplish that would be to lag bolt some 2x8 "clevices/bearing points" onto the inside of the foundation wall, and then hanger them back onto the double 2x6 on the other side (the one in the drawing). That might let me, if I'm careful, replace that wood, at least in that section, for the purpose of the bathroom that I wanted originally. It requires moving some plumbing, but that had to happen anyways. I'm just not sure if that's structurally-sound-enough, so perhaps if the carpenter will agree I can also put some jackpots down to the basement to help hold everything stable while also using bridge blocks between.

I should mention that when I first moved into the house 10 years ago, one of the first things I did was to jackpost the area where the two 2x4 doubles intersect the 2x6 double. The carpenter said I may have saved the house doing that because the double on the right is compromised to the tune of 80% because someone decided to put the toilet drain right through that beam! Then they just blocked it down to the dirt with a 4x4, which is a very lazy fix. May explain the sag in the floor! To that end, I certainly could add more jackposts if necessary. I tend to like to overbuild things a bit anyways.

When you say "... I don't see why you can't take out a lot of what's there and install what you really need", do you mean that I should consider replacing all those 2x4s where possible, or, reading that a different way, are you saying that I should modify my design to be a curbed mud deck shower to avoid ripping the 2x4s? Just want to be sure I'm understanding your opinion on that.

I suppose if the 2x8 replacement is a valid option, you wouldn't see any reason why I could revert back to the curbless option with the mud base, right?

Thanks again for your answers. It gives me lots of good options to think about.

otrex 02-19-2019 01:52 PM

Also, as a follow-up, assuming I can get all this to work, do you perceive any issue with using Laticrete 3701 Fortified Mortar Bed Mix for the Dry Pack Bed? I like the concept because it is premixed, but also it adds their 3701 latex. With the thinner mud base, that might be very helpful.

I spoke with Laticrete and though they have premixed "209 Floor Mud" they were adamant that 3701-fortified Mortar is superior in every way.

Lou_MA 02-19-2019 02:08 PM

How thin will the deck mud be at thinnest point?

If the min thickness is 3/4" or more, I'd skip the fortified mud. It'll be overkill in the sense that it'll give you way more compressive strength than you'd ever need, plus it's more expensive and will be more difficult (sticky) to work with. Sand and portland work just fine, I wouldn't complicate things.

otrex 02-19-2019 06:27 PM

Thinnest side is 15/16" thick and thickest is about 1.5".

I also want to see how this floor joist issue turns out. I would think If I'm building on something with higher-than-normal deflection I would want much stiffer dry pack?

cx 02-19-2019 06:33 PM

Nope, you wanna correct any excessive deflection problem before you place any deck mud bed, Kevin. You're not depending upon your "dry pack" for any structural properties aside from compressive strength.

My opinion; worth price charged.

otrex 02-20-2019 06:02 PM

So, I had another chat with Laticrete today and they conceded that the 3701 fortified mortar is probably overkill for a dry pack bed.

They're back to recommending their 209 Floor Mud mixture:


Anyone work with this before? Is it a 5:1 mixture or something else? Given that I am going to build this dry pack bed myself (first time), I think maybe this is better than trying to mix up a batch myself.

cx 02-20-2019 08:53 PM

I disagree, Kevin. Not much in the world of construction simpler than mixing some sand and some Portland cement. Five scoops of this, one scoop of that. Mix. And there's nothing that makes better deck mud than that.

If you really wanna make life easier for yourownself, get you a Bucket Mortar Mixer.

Mix all your mud, plus a little, dry in 5 gallon buckets and have them sitting ready outside your shower. Add a little water and mix as needed. Less than 2 minutes each. Great when working alone, which is nearly always my case.

My opinion; worth price charged.

otrex 02-28-2019 03:02 PM

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Just wanted to post some follow-up just in case anyone finds it useful.

After being told that all my joist were 2x4, I decided to hop into the crawlspace to inspect. I was delighted to see that the contractor had been fooled - I actually have dual 2x8s running out to the foundation with 2x4 crossers in between! He was deceived because 1940s construction did not use hangars, and in this case a thin strip of wood was positioned under the 2x4s to hold up insulation. Though I previously removed all the insulation from the floor in favour of making the entire crawlspace walls insulated (one of the best things I've ever done in this house), it left traces of insulation paper hanging from that strip which obscured the 2x8s and made them look like 2x4s.

So, long story short, in the diagram from earlier where I show double 2x4 beams, they're actually 2x8! :yipee:

I have directed that the 2x4 crossers be removed and new 2x6 crossers with hangars be placed instead. In addition, I have had the centers changed to 12" and bridging blocks added to reduce non-uniform movement across the floor. The shower area is on 6" centers with clearance left for the Kerdi Line drain.

Also, since the beams were 2x8, I was able to have the shower area framed with 2x6s and simply installed lower than the rest of the bathroom area. Coupled with the fact that my house has 3/4" plywood over 3/4" floorboards, leaving the shower area with only a single 3/4" plywood base means the depth that needed to be cut out of the 2x8 beams was only 11/16". Now I can make the dry mortar base the full thickness by using the extra depth provided by the double-thickness of the sheeting in the bathroom area.

Here are some photos!

jadnashua 02-28-2019 06:51 PM

The 'crossers' (called blocking) don't change the deflection rating for the subfloor. The will reduce the tendency for the joists to twist when exposed to a load, and will help change the resonant frequency of the floor which can make it appear to be stronger. They do add weight to the overall floor assembly. They do not need hangers. They help make the things safer prior to the installation of the flooring, but that isn't as big a deal when the joists are short. On a new construction, with longish lengths, they can wobble if you walk across them prior to the subflooring being installed...the blocking prevents that from happening. The subflooring, once properly attached does that, especially if there's a finished surface on the bottom, making it a box beam.

otrex 02-28-2019 07:24 PM

I was actually a professional framer for a time a few years back, so my use of "crossers" was not meant to mean the blocking (and yes, blocking definitely doesn't need hangars). I only stated it that way to be more clear on referencing the new joist running left-to-right in the picture rather than the foundation-bearing beam/joists running "top-to-bottom" in the picture.

Yes, I realize the deflection rating wouldn't change across the structure as a whole. I am just trying to reduce any "point deflection" by sharing the support across multiple crossers instead of the previous version of this floor which was independent 2x4s.

The plywood which is next to go down will be glued and screwed to help with that goal. There are now also two jack posts underneath the 2x8 beam which runs inside the bathroom. Again, just an attempt to reduce any point deflection.

otrex 03-01-2019 09:14 PM

A quick question for someone who might know: In the shower area, I am using Kerdi Board. The upper portion and entire back wall will feature bevelled subway tile, and that installation is fairly standard and straightforward (I know the basic concepts, but I'm hiring a tile installer for it regardless).

What is less standard is that I am using a 100% PVC beadboard on the lower half of the walls, both inside and outside the shower, divided by super-clear glass to give the visual impression that the room is large. The beadboard is tongue and groove assembly and I'll be adding extra insurance by using thin bead of sealant inside each groove.

I must take a moment here and mention that I previously tested the beadboard by lying it flat on the table and pouring water on it, then leaving it for an hour. After dabbing the water off that stayed on top I opened the tongue and groove and found no water at all inside. This, I believe, is an even-tougher test than the beadboard will ever face because it gets installed vertically. And since it's 100% PVC, it won't have any issues with rot or decomposition.

My question is this - the manufacturer of the beadboard recommends gluing or nailing the beadboard to the wall, but of course, I am not going to use any nails through the Kerdi board. Instead, I will use an adhesive.

The adhesive/sealant I am looking at is Sikaflex 221, which is described by the manufacturer in this manner:

Sika Sikaflex-221 Non-Sag Polyurethane Sealant White is a one component, moisture-curing polyurethane adhesive sealant that is used for creating a permanent elastic seal for substrates such as metals, wood, paint coatings, ceramics, and plastics. It is a non-corrosive, low odor, high quality sealant that is resistant to diluted acids, limewater, seawater, freshwater, weathering, and aging.

Anyone see any potential issue using this to mount the beadboard onto the Kerdi Board?

otrex 03-04-2019 10:10 AM

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Just wanted to update this thread now that I have completed the dry pack mortar bed.

In the end, I did use the Laticrete 209 Floor Mud mix. It was about 25% more expensive than mixing it myself would have been, but for my first time doing a shower bed, I am okay with that.

I found the 209 mix to be relatively easy to work with. Given the cold weather outside I was mixing in 5G pails inside, and so I found the best way to get a good and complete mix was to use my gloved hands and pour from one bucket into another and back again. I had been using a large mixer on my hammer drill, but this mix is thick enough that it threatened to burn my drill out completely so I halted it before that could occur.

To help with getting the 1/4" drop correct, I made an MDF "blank" of the Kerdi Line drain and then temporarily screwed it down to the floor. On the other side, in order to account for the thickness of the Ditra which is going outside of the shower, I stapled down thin wooden strips. That way when I dragged the level across, I could simply push down on both of these items in order to set the correct level "automatically". I also purchased a hard rubber float and rubber mallet so that I could compact the mixture in place before dragging the level across and then finishing with a metal trowel.

(This is not a new technique, just including it in case someone else reading this is going to try a shower bed for their first time too).

In any case, 14 hours later and the mixture is setting up very well. Minimal loose bits on top and very flat surface (which is to say, consistently sloped at the desired 1/4" per foot).

In retrospect, this was just as easy as my alternative shower floor, proposed at the start of this thread, would have been. So if you're a bit intimidated by this work, you shouldn't be. As long as you closely follow the traditional method instructions, and watch the water mix carefully, it's pretty simple.

I am glad I had a second person for help with mixing - because the job is a bit tiring.

Finally, I should note that it appears the Laticrete 209 mixture is a 4:1 mix.

otrex 03-12-2019 09:46 PM

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Hello again, everyone.

So, everything has gone well up to this point, and now that the Kerdi Board is on (I wet-shimmed the walls to make them flat!), I have had to hire a tiler to apply the Kerdi Band to the wall joints, Kerdi to the Dry Pack floor and Ditra to the rest of the bathroom.

To make a long story short, this fellow I hired is the top guy on Homestars for the Greater Toronto Area, and is a dedicated tiler. Within an hour of him starting, however, I was noticing several things which are not approved by Schluter. When I raised this matter, I was told "don't believe everything the manufacturer tells you".

Fair enough, but after his departure today, there are some problems (see photos below).

First, he applied Kerdi to the floor and simply wrapped it up to the sidewall which is not the correct procedure. Unfortunately he failed to get proper thinset mortar adhesion and it is peeling away already. I should note that I got him several bags of Schulter All-Set to use - the best stuff Schluter makes.

In addition, I noted that several strips of Kerdi band were not adhering to the walls, and I noted that in some places it is simply because his mortar band is not as wide as the Kerdi band.

I want to point out here that we also had a small argument about the need to apply Kerdi Band to the joints in the Kerdi Board and over the screw heads as per Schluter recommendations. He contended that thinset mortar would keep water our whereas I contended that thinset mortar is not a water barrier. Thankfully, I know from reading these forums that I am 100% correct in my argument, and I insisted he put those Kerdi bands up. He refused on the screw heads and so I will be putting those up myself.

This is the top-rated guy in the area... not sure what to do.

I'm thinking I point out these improper Kerdi Band applications and ask him to remortar? Now that the Kerdi is down on the ground and mortared to the wall (instead of using Kerdi Band like Schluter demands) it is too late for me to do anything about that, and I should just insist he remortar it to ensure adhesion?

Any advice on how to proceed would be ideal. It was a real fight getting any tiler here in the Greater Toronto Area. The housing boom that's been going on here for the better part of 2 decades has made tradesman extremely hard to find and also very expensive, so I hesitate to fire him at this juncture.

cx 03-12-2019 11:57 PM

Some wider views would help with perspective there, Kevin, but that looks like very sloppy work to my eye. 'Specially for a "professional" who is being paid for the work. When such persons tell you it's not necessary to follow manufacturers' installation instructions, it's time to find someone else to do the work.

Surely you can do a whole lot better than that yourself and follow the manufacturer's recommendations in the process.

There is nothing at all wrong with wrapping the Kerdi membrane from the floor up onto the walls, by the way, so long as it's done properly.

My opinion; worth price charged.

Gozo 03-13-2019 08:19 AM

It’s not wise to disagree with CX, so I won’t. I just had to comment on this one.


Surely you can do a whole lot better than that yourself and follow the manufacturer's recommendations in the process.
If you can wet shim the walls and put up Kerdi-board, why did you decide to hire out the fun stuff? I’m just a DIY who’s been there before. My thought on looking at the pic you posted was “OMG!”. He either doesn’t know how to work with Schluter products (hey, even I can!), or doesn’t care.

You shouldn’t have to follow behind him or argue about the quality of the work.

How much sleep you going to lose over the coming years waiting for the whiff of moldy framing you know is waiting down the road? Been there, done that.

speed51133 03-13-2019 09:50 AM

fire this guy asap.....

cx 03-13-2019 10:04 AM

Jeff, you feel free to disagree with CX any time you feel the need. Best if your opposing opinion aligns with tile industry standards, but even that's not a requirement, eh? :)

Davy 03-13-2019 11:23 AM

I hope his tiling skills are better than his Kerdi skills. I'd send him packing and take my chances on finding someone else or do it myself.

makethatkerdistick 03-13-2019 12:08 PM

I would rid myself of this contractor asap if I were you. This is atrocious. Just imagine if you have to argue with him over tile work later. At least, at this point you can still stop the disaster. If not carefully remedied, chances are this won't be waterproof.

otrex 03-13-2019 07:56 PM

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Thanks everyone, my gut instinct was indeed to fire him, but I had to show some restraint for the following reasons:

i) Another tiler will be impossible to find

ii) I cannot afford to tear all this Kerdi Board back out and start again

iii) Ontario (Canada) law requires that I give him ample opportunity to correct his mistakes, or, if I choose to fire him without allowing him that chance, he can bill me in full for everything he has done up to that point, regardless of quality.

He came back today, as promised, and I pointed these things out to him. He stated "don't worry, I will add mortar to those Kerdi Bands and take care of that, but in the meantime I would like to get the floor down".

Given that all these issues were above the floorline, I agreed, and he did put the floor down with considerably more skill and care than the Kerdi. That being said, I still noted a few tiling technique mistakes (which should not be happening given that I have no tiling experience). For example, he was not back-buttering the 6" x 36" tiles. I asked him why not and he explained that he makes his mortar a little bit runnier than most and this allows for proper coverage. I still insisted that he back-butter, and for perhaps 75% of the tiles, I saw that he did. The others I was not present to see (as I was running tile for him).

He did carefully check the slope in the shower, so at least that is preserved correctly.

Given the situation, with my hands somewhat-tied legally, I have elected simply to watch him work as much as possible and then provide direct feedback/criticism in the moment. If he quits, so be it, and I will not pay. If he fails to follow my direction, I'm in my legal right to fire him (since I would have already afforded him an instant opportunity to correct his mistake). Today, at least, he took my criticism rather well, and made adjustments when I demanded them. I hate being "that customer" but ultimately I have to know I'm getting it done as close to correct as possible. This fellow isn't exactly cheap (C$10 per sqft, and I have to supply all material).

Here is a quick photo of the tiling work on the floor. I went with 1/8" gaps as per advice in this forum. I think it's definitely the right call for the floor. For the walls I intend to use 1/16" because it's 3" x 6"subway tile and 1/8" can look a bit large. I am even electing to use a stacked layout for those tiles since I have the shower walls laid out so there are no tiles needed to be cut at all.

Apologies that I cannot get a better photo as I don't want to walk on the tile. At the very least you can see he seemed to use an appropriate amount of wedges and spacers for the job. Note the Deco-SG window track in the floor tile more than half-way back and the Kerdi Line drain against the back wall (the dry pack mortar bed came out perfectly-aligned for the drain).

Just to follow-up on another user's post a bit earlier, yes, after watching the process I will now do future tiling myself. I did not see anything particularly difficult during the floor tiling, and I continue to believe that an educated and caring amateur can obtain results as good or better than a non-caring professional any day, especially if that professional doesn't care about manufacturer's specifications.

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