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Unread 03-19-2021, 10:20 PM   #1
otrex
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Help with New Kitchen and Shower Project

Hello everyone,

Some of you may recall me from a couple of years ago where I asked for assistance in planning my new bathroom with a curbless shower. Thanks to your help, I achieved very admirable results and a beautiful shower that I was fortunate enough to enjoy for a little more than a year before life took us in a new direction.

We sold that house - and with the market red-hot we received multiple offers, but for every single bidder the message was the same: The showpiece was the bathroom and shower. Everyone loved it! Just wanted to share that with the folks who remember that project since your solid advice helped to make that happen.

We moved a little further outside the big city into an 1880's Victorian. It's very nice inside with a lot of the original details preserved. On the back of the house someone built a nice little loft style apartment. I would estimate the construction somewhere between 1890 and 1920, mostly because they used the same cut fieldstone as the main house.

In any case, another small addition was made later and it is positioned on the outside of the brick building. It was a 3-season room which was eventually insulated so well that it could be used as a 4-season room if someone would add some ducting (or in my case, I added a split-air ductless system for this room since I did not want to run ducting through two foundation walls. The foundation on that part is poured concrete, and we know from the seller that the previous family was in the concrete industry and built it around 1940 or so. That concrete runs right alongside the cut fieldstone creating a double-wide foundation where they meet (and the reason I didn't want to bore through it for ducting).

We have an elderly family member that needs to move into this apartment, and so I am dead set on making her life as happy and comfortable as possible. But this little apartment is missing both a kitchen and a shower, and so I'd like to add one of each for her.

While I will follow-up with the full floorplan and pictures soon, I am being pushed to make a decision on the floor for the kitchen which is planned to go into that 3-season (now 4-season) room. I was hoping someone here could help me with that.

I have been under the foundation and found that it is open on one side meaning I will close it in later with insulated framing to keep animals out. It is a very solid poured concrete and the joists span at no more than 16" centers. They appear to be true 2x8s. The span is a little under 8ft. It is capped with painted hardwood of some kind. It appears to be 1" or 1.5" thick wood strips. Someone has already used a large amount of insulating foam in the entire underside of the joist - the foam is very dense and probably contributing to the overall stiff feeling of the floor.

Here is the problem: The floor has a rather consistent slope away from the building. At 8' the drop is about 2". I looked at levelling it through a combination of 3/4" plywood and liquid level, but it is not possible to accomplish that without going over the sill plates of the two outside doors, and so I also ruled out "partially leveling" it too, of course, since that's just going to take a relatively-flat (albeit out of level) surface and put a kink in the middle. I recall from discussions here before that "flat" is necessary for tile, and not necessarily level.

I have jumped up and down a bit on the floor (and I am 220lbs) and found it to be quite stable. I cannot detect any flexing in the floorboards. Of course, there is bound to be some.

My instinct is to screw down 5/8" T&G plywood right into the existing decking to reduce any flexing and to do so using large beads of glue as a bit of a "wet shim" to help take care of any dips. The floor doesn't have very many, but I'm thinking the glue might help shim them a bit as it will settle where necessary to accomplish that. Once the plywood is down, I am thinking of using a layer of Ditra for a bit more forgiveness before tiling over the whole thing with a larger format tile.

My questions are:

i) Given these specs, will this floor be stiff/flat enough for tile once I complete the above proposed procedure?

ii) Can I get away with OSB or should I use plywood? I shudder at the cost of either option ($50 per sheet on OSB and $70 on plywood). I assume plywood is the safer choice to avoid water issues in the kitchen, but with Ditra protecting a bit, maybe it's not as much of an issue?

iii) Is my proposed procedure sound? Anything else I should be checking/doing here?

iv) Am I better off building the kitchen on this floor and forgetting about tile? It's a bit of a "country kitchen" look, to be sure, and I would want to add a fresh coat of paint, but as the rest of the house is rather elegant, I feel leaving this might be a bit of a mismatch.

Thanks in advance for your thoughtful advice. Soon I will have details on the very challenging shower build I've been planning and I'll be pleased to ask for your feedback on that too (as it is a rather strange build).
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Unread 03-19-2021, 11:04 PM   #2
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Welcome back, Kevin. Same ol' cat, eh?
Quote:
Originally Posted by Kevin
It is a very solid poured concrete and the joists span at no more than 16" centers. They appear to be true 2x8s. The span is a little under 8ft. It is capped with painted hardwood of some kind. It appears to be 1" or 1.5" thick wood strips.
Gonna hafta help us old folks a bit there. If you have a wood framed floor, where is the "very solid poured concrete?"

i. Not sure. See above. But if you have a wood framed subfloor with 2x8 joists spanning only 8 feet, your joist structure is OK. The "painted hardwood" is of the T&G style? Any idea just what hardwood it might be?

ii. I would recommend you use plywood any time you're gonna bond anything to it. And remember them are only them little bitty Canuck dollars, eh? The minimum thickness would be nominal half-inch and the T&G would not be necessary. That's according to ANSI, of course, I dunno what TTMAC might require.

iii. Oh, I'm sure there's lots more you should be checking/doing.

iv. Above my pay grade. Best to ask Mrs. Kevin.

My opinion; worth price charged.
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Unread 03-20-2021, 01:16 AM   #3
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Thanks for your excellent feedback, as always.

Answers to your questions/thoughts:

"Where is the poured concrete?" - Yes, apologies for that, I realize it could have been read a couple of different ways now that I read it back to myself. What I meant was, someone poured a custom concrete foundation for this room alone, and on it they placed the true 2x8" wooden joist. I mentioned the concrete only to confirm that the room was not held up only by deck posts or something similar. It walks out onto a very tall deck and initially I had thought perhaps there were concrete pylons or even deck posts involved. I was pleasantly surprised when the snow melted and I found a nice poured foundation for the joist to span across! This room was definitely the last to be built and was at least 30 years after the main addition, so I feared someone perhaps had used substandard materials to hold this extra room up.

i) I cannot say for certain if the decking wood is T&G. I suppose it certainly could be though, given the construction date of around 1940. It does feel really solid, and so I suspect it is either T&G or that it is thicker than modern standards (or both). I suspect it may be maple or pine, but it feels awfully heavy/dense for pine. So hard to say though with it being painted and not being a wood expert.

If I find a spot where the paint is chipped away, do you think you'd be able to hazard a guess as to the wood type based upon woodgrain?

For checking if it's T&G, I suppose I could try to ram some flat metal in between and see if I hit a tongue?

ii) Yes, these Canuck bucks still hurt when they get spent in large groups though! I agree though - I feel plywood is going to be worth the extra investment over OSB when there is mortar involved (which I assume OSB soaks up like a sponge and then uses that moisture to destroy itself).

iii) Other things to plan/do - I am going to hop back under the foundation and confirm that I have at least 2x8" on 16" centers. If they turn out to be true 2x6" joist on 16" centers at 8', would that spoil the margin of safety for tile (assuming all other parameters are the same)? Would you be tempted to use a decoupling membrane like Ditra on top of the plywood even at 2x8" joist? I have read that sometimes the older floors built this way can swell/contract with the change of the seasons.

iv) Mrs Kevin says she likes it either way (as-is or tiled) though I feel like that might be a trap depending on the final quality of my work! I'll have to tile this on my own as the professionals are booked solid until year-end at present.
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Unread 03-20-2021, 09:03 AM   #4
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Sorry, still confused. Now sounds like the floor joists are sitting directly on, and are fully supported by, a concrete SOG foundation.

i. Un-paint a small portion would be my advice. If it's a thick as you surmise (I'd certainly wanna drill through it to determine the actual thickness. A small hole saw in an out of the way area, drilled through a joint, would quickly show both the thickness and the center-match.

ii. Yeah, I guess when it's only Canuck dollars coming in, it doesn't matter how small they are going out.

Some manufacturers of thinset mortars don't like their products used to bond to OSB. And I've never found it a good idea to try to bond to OSB with any kind of adhesive. Just doesn't work well in my experience.

iii. I'm still confused about "this way."

iv. Yes, clearly a trap. You must 'splain her that a decision is required! Which, of course, is easy enough to say from a fella been single these 75 years.

My opinion; worth price charged.
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Unread 03-20-2021, 05:23 PM   #5
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Not to worry - I have been known to cause confusion!

Yes, that is correct. The joist are sitting fully on the concrete foundation. My feeling is that the owners in the 1940s wanted a porch, but the house sits so high above the surrounding ground (very tall basement!) that they needed some way of holding up that porch. So they poured this new section of foundation just for the porch and it appears to be at least 6" thick and the joists of the porch bear fully on that 6". I think you could potentially park a truck on this floor.

This theory would also explain the uniform tilt of the floor, perhaps? 2" at 8' just happens to be the minimum necessary to get water to flow away, right? Little did these owners know that sometime later this porch of theirs would have walls built on top, but that may explain why such a large tilt while still being relatively flat?

I had a look today (with my father, who knows a bit more about wood types) at a portion of the decking that has had some paint wear. He thought it looked like Maple, and his feeling was the thickness was 7/8". He said it was almost certainly T&G decking based upon his inspection into the cracks. I agree with him - there is not a single bit of daylight even between the largest of gaps - it does appear to be a wooden tongue in those spaces.

I still have to get under to confirm the joist thickness, but so far so good, I would assume?

Hopefully my answer on the concrete foundation makes more sense and helps with determining if tiling will work and if Ditra is a good idea.
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Unread 03-20-2021, 06:07 PM   #6
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Yes, the 1/4" per foot would be the recommended pitch for an exterior deck in my part of the world, Kevin.

We generally (tile industry) consider SOG concrete floors to have zero deflection and if your joists are fully supported on such you can consider them to have the same. Thickness wouldn't matter if they're in good condition.'

And even though Maple isn't the most rigid wood, at 7/8ths" and T&G I would consider your between-joist deflection to be quite good. A layer of nominal half-inch exterior glue plywood over that would make a very good subfloor for a ceramic tile installation. And Ditra would be an acceptable tile substrate.

If, of course, Mrs. Mike doesn't favor a lovely maple floor in her kitchen.

My opinion; worth price charged.
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Unread 03-20-2021, 08:59 PM   #7
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When you say SOG, I think you are referring to "Slab on Grade" which means, I believe, that I have been unclear in my description. So, just to confirm this, I have made a diagram which will better describe the situation. I'll attach it below. I have deleted the walls from the diagram for clarity, so this shows the situation as it would have been in about 1940, though since that time someone put a room on top of that floor.

I said before "6 inches thick" which may have implied SOG, but it is less confusing to say 6 inch WIDE concrete foundation walls, though there is still a span across an outdoor crawlspace of about 7'. It may actually even be 8" thick concrete which would reduce the span slightly, but I wanted to be as conservative on the estimate as possible.

I realize now I also said "the joist sit fully on the foundation" which again, is my mistake for not being clear as that also implies SOG. I come from a framing background, so what I meant was that the joist use all the available space on top of the concrete foundation walls rather than just bearing to a minimum standard (which if I recall when I last framed a house was 3"). My apologies again for my poor description - hopefully the diagram does a better job.
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Unread 03-20-2021, 10:00 PM   #8
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Well, that was a very long trip around the block, but your drawing clears up the matter for me. What you have is an unsupported span of 7 feet and your joists could be as small as 2x6 and still meet the necessary deflection requirement.

My opinion; worth price charged.
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Unread 03-21-2021, 10:33 AM   #9
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Well, I appreciate your assistance even if it was partially for some fictional scenarios due to my poor selection of words.

Thank you - I will have some kind of a decision today from a certain young lady about tile vs. leave as-is and that will get this part of the project headed in the right direction, I hope.

I'll update this thread with the shower questions soon - and a diagram to start this time, I promise!.
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Unread 03-26-2021, 07:53 PM   #10
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A quick follow-up question or two in regards to the plywood selection for installation on top of existing T&G 7/8" maple before tiling:

i) It looks like 1/2" maple plywood prices have risen dramatically and it's almost the same price as 1/2" oak. Are either of these considered more suitable for tiling and/or more stable when installed over mild imperfections?

ii) My intention is to glue and screw the plywood and use thick beads of the glue as a "wet shim". Should I be using subfloor glue which is a bit more thin or something more like an all-purpose which can probably hold up to a bit more pressing before pressing out? I'm thinking the latter if my intention is to use it as a shim, but I'd welcome feedback on that. The variations in the floor, as shown, are not particularly bad.

iii) How much expansion joint space is necessary between sheets of plywood in this application? I would assume 1/8" from walls and other sheets?
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Unread 03-27-2021, 07:17 AM   #11
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Kevin,

You don't need or want 5/8" maple or oak plywood. You do want plain old 5/8" ply with a face grade not lower than "C" and the plys that make up those panels should be stuck (laminated) together with a moisture resistant glue - commonly marked as "Exposure 1" or "EXP1". Example' 5/8" B/C EXP1.

IMO, you ought to get yourself a mess of screws and run one into each of those boards where each crosses over a joist.

I would not attempt to run beads of construction adhesive with the hopes of those beads acting like a shim. It is more likely they will act as support - holding up either side of the ply along the length of the beads while the center of the ply is unsupported. If you really want to glue it down you'd want a full spread of glue covering the entire area that you intend to cover with the ply.

1/4" gap to the wall will be fine. 1/8" between sheets will be fine.
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Unread 03-29-2021, 02:14 AM   #12
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Thanks kindly for that - I went with the standard spruce plywood at 1/2" despite it being basically the same price as oak or maple (yikes, building materials are way up in price right now).

I put a lot of screws into the sheets (~80 per sheet) and was able to get a few lines of thin subfloor glue down too. It was quite thin glue so I doubt any buildup will be possible. .

For the 1/8 expansion joints between the plywood sheets, do I fill that with anything (other than the mortar which is sure to fall in there when I prepare to add the Ditra)? I saw someone advocating for filling those voids with tile adhesive, but I am wondering if there is a better option?

I would assume, of course, that I won't be tiling right to the edge of the room so the 1/4" there is fine left empty. Then the baseboard covers that gap, I would imagine.
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Unread 03-29-2021, 08:17 AM   #13
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Pay no attention to the plywood joints has long been Schluter's recommendation when installing Ditra. I'm not aware of any change in that policy, but you can ask them if it'd make you more comfortable. 800-472-4588. Do let us know if they tell you differently.

Pay no attention as in don't intentionally fill them with anything and don't try not to fill them with the bonding mortar for the membrane.

My opinion; worth price charged.
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Unread 04-01-2021, 04:44 PM   #14
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I did call Schluter and I can confirm that both the American and Canadian offices are instructing customers exactly as you described.
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Unread 04-03-2021, 10:06 AM   #15
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Just wanted to follow-up with an update:

Had the gas line for the range installed and so was able to complete the Ditra the next day. A first time putting down Ditra for me and I noticed a few things:

i) Mixed the All-Set to the thinnest recommended water mixture. Had my doubts if it would hold a notch, and while I wouldn't want to run it any thinner than that it still did hold a notch.

ii) I made sure to key in the thinset with the flat side of the trowel before notching. I think that may have assisted me a bit as my first piece I feel went down without quite enough mortar underneath. It's still well stuck down after the 12 hour drying time, but I wonder if I did not key in the thinset if that would have still been the case.

iii) Though the bag says you get 70sqft out of one bag of All-Set, I completed all ~100sqft with one bag. I suspect using the max water level helped to stretch it out a bit but also perhaps I was a bit stingy with the thickness of the mortar as I applied it? By the end I was literally scraping it out of the bucket in order to use every last drop as I didn't want to open a new bag for a couple of square feet.

iv) Because of the odd layout of the room I had no way to get the last full sheet in place without having to walk on other freshly-laid sheets. I put down a piece of 1/2" plywood to spread my weight out a bit. Schluter seems to want only 75lbs of pressure during the wooden float stage and so I assumed that this was so keep from squeezing all the mortar out from between the Ditra and the plywood?

v) Just before starting this job I decided to rip out the door between the living room and this old sunroom (soon-to-be-kitchenette). It was an outside door anyways and this sunroom was already fully insulated. Not only did the inswing of the door get in the way of clear passage but I suspected someone had heavily blocked/shimmed the opening down to fit the door and I was right. Behind the casing I found a full brick archway and it had been blocked down by more than 12" on the top and 6" on each side! I will finish it up as a nice interior archway instead of a closing door. You can see some of it in the photo - not fully ripped out yet, but with the brick now exposed.

All-in-all, I am relatively happy with my first use of Ditra. I was more careful than the professional that I hired for this same task in my last bathroom project and I've always felt that a careful amateur can outperform an uncaring professional (not suggesting that all amateurs are careful or that all professionals are uncaring, of course). That being said, next time around I hope to perform even better with this product. And we'll find out soon because I have that upstairs bathroom to do in the next week or two and will post in this thread here on that topic soon!


QUESTIONS


As readers of this thread know, this room is now very flat but also slanted at a very consistent 1/4" per foot as it used to be an outside porch.

Do I need a tile leveling system if I am to install floor tile and will such a system get good results if the floor is on a consistent tilt?

My feeling on this is that if I avoid the use of any large format tile (LFT) I can probably get away without using such a system, meaning I'd need to select tile that is under 15" on any side. That seems reasonable to me though as the room is quite small (about 7.5' x 13.5') and so it won't look out of place.

I welcome thoughts on the tile leveling system and/or my thoughts of using smaller format tile. Or any other thoughts/questions that you might have too as this will be my first time laying an entire tile floor by myself (though I did lay a couple of tiles after firing the tile guy on the last project).
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