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Discussion Starter · #1 ·
We are in the planning stages of renovating our guest bath. There is original contractor grade white square tile in there now. I haven't pulled the tile up yet but from what I can gather after pulling out the floor vent is that there is what appears to be a 1/2" to 3/4" mortar bed that the tile rests on. I can see the plywood subfloor as well.

My question is after taking all the tile and mortar off the plywood, can I just go with a 1/2" cement board underlayment over top the plywood? Or someone even suggested going with the Ditra XL uncoupling membrane (Ditra XL is the thicker form). Anyone use Ditra?
 

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1/4 inch cement board is more of the standard for floors, not 1/2".

Ditra vs. cement board has been discussed many times on this forum, Do a search and check around what has already been said.
 

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Discussion Starter · #3 ·
1/4 inch cement board is more of the standard for floors, not 1/2".

Ditra vs. cement board has been discussed many times on this forum, Do a search and check around what has already been said.
I guess if I went the 1/4" cement board route, I'd have to build up the mortar as I would like to keep the floor roughly the same height as the one in there now. Although if the floor turned out 1/4" lower, I probably wouldnt even notice.
 

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I guess if I went the 1/4" cement board route, I'd have to build up the mortar as I would like to keep the floor roughly the same height as the one in there now. Although if the floor turned out 1/4" lower, I probably wouldnt even notice.
I'm not a tile pro, I'm sure someone else will chime in soon, but if you need that extra 1/4" height, you might be better served by adding a thin layer of plywood. under the cement board. A lot depends on the condition of the existing subfloor, the size of the area being tiled, the joist structure below the floor, the size and type of tile you are going to install, etc.
 

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Tileguy
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Hi Sydmax,

What you've got now is a basic mud-job which should be at least ¾" thick. If you're going to remove it, you should replace it with a layer of plywood to take some of the height and add strength. Then you can install ¼" concrete backer or a membrane such as Ditra. The total thickness is slightly adjustable and depends on several things including the level of the toilet flange and your desire for the finished height. The minimum thickness of the underlayment grade ply should be ⅜" or thicker. Thicker of course is better.


Sydmax said:
I guess if I went the 1/4" cement board route, I'd have to build up the mortar as I would like to keep the floor roughly the same height as the one in there now.
No, the bold statement will not work.

Alternatively, you could tile over the old tiles if the conditions were right.

Jaz
 
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Discussion Starter · #6 · (Edited)
Hi Sydmax,

What you've got now is a basic mud-job which should be at least ¾" thick. If you're going to remove it, you should replace it with a layer of plywood to take some of the height and add strength. Then you can install ¼" concrete backer or a membrane such as Ditra. The total thickness is slightly adjustable and depends on several things including the level of the toilet flange and your desire for the finished height. The minimum thickness of the underlayment grade ply should be ⅜" or thicker. Thicker of course is better.




No, the bold statement will not work.

Alternatively, you could tile over the old tiles if the conditions were right.

Jaz
Thank you for the replay. I knew that mud beds are 3/4" or even more but when I looked at the layering of flooring when I removed the floor vent, it certainly looked like 1/2 or so of mortar which led me to believe a builder's special tiling job from when the house was built.

Bathroom is not big so it's not a lot of tiling work. I think I might go with your option of 1/4 ply, then either cement or pay the extra for Ditra (never used Ditra before so I kind of want to give it a test run in a small bathroom!). I believe the joists below are 16 o.c. a 2x10s so I would think from a structural perspective, I would have no real issue going with cement or Ditra, especially if I add another layer of ply. Obviously will have to check the state of the subfloor once I removed the old tile and all the mortar but I have no reason to believe it's in bad shape.

Thanks!
 

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Tileguy
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I do not recommend installing any ¼" ply or OSB as it's a waste of time and money since it'll add very little strength to the floor. It's not recommended by anyone in the biz. You want/need something structural anyway. I would go with min. ½" underlayment grade made with ext, glue, rated exposure 1. Depending on the details I'd consider even thicker ply but compensating with standard ⅛" Ditra instead of concrete backer. Either will work well with the proper subfloor framing and subfloor system.

Tell us about the framing will ya. You said 2x10's @ 16" but wants the unsupported span and do you know their species and grade? How old and where is the house? Condition etc.?

You'll love Ditra if you've ever tiles using other methods.

Jaz
 

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Discussion Starter · #8 · (Edited)
First off my bad, for some reason I thought you said 1/4 ply. I must have misread.

House is in NJ and was built roughly 23 years ago, part of a tract development. I do not know the species or grade. I want to say the rough span might be 12 feet but I am seriously just guessing there as I haven't really measured it. In terms of condition, pretty good and I have not had any instances of any structural problems, etc if that's what you are driving at. Current set up in bathroom seems fine and I've noticed no ceiling issues in the family room below the bath. Sorry I can't provide more detail than that.

I might just go with your 1/2 ply and then regular DITRA as I think that will have the new floor at roughly the same height for the transition into the hallway. I am curious to use DITRA and while pricey, since it's a small bathroom it seems it won't cost me an arm and a leg. I've done a few tiling jobs, not a lot, mostly on backerboard or even concrete slab.

FWIW - My brother in law just told me he thinks the joist spacing is 12" not 16". He has a house in the same development. I swear when we bought the house a couple of years ago my buddy who is an inspector said 16".
 

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Tileguy
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16" oc is standard. Is the subfloor ¾" ply? Measure the span accurately like; 12'3" etc. The species and grade matters, but most of the time people can't identify them.

Since the house is young, I'm sure it meets L360 deflection for both the joists and subfloor. We just like to start with the basics so we can understand how it's built. Thanks for the location as that helps us picture how the house is built to a degree.

I asked condition cuz sometimes people (or plumbers) have added pipes and hacked into a joist with notches or large holes.

You can buy Ditra at the orange place or a real tile store in your local area. If you're lucky they'l sell it by the linear ft. Anything under $1.75 a sq. ft. is good.

Jaz
 

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Discussion Starter · #10 · (Edited)
It's all original stuff in that bathroom so at least it seems likely no one did something crazy after the house was built. But who knows. Hahaha.

Subfloor does appear to be 3/4" ply. At least I saw 3/4 ply below the mud bed when I took a quick look at the layering when I took the floor vent out. I am going to assume, for now, 16" o.c. since that's why my inspector said and that tends to be standard but as we get closer to starting the project, I'll investigate.

But thank you for giving me some good insights and as we get closer I might revisit this thread. But for now, assuming everything checks out, I'll probably go with another 1/2' play on top of subfloor and then give DITRA a go.
 

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Discussion Starter · #11 ·
FWIW, did some digging around. The master bath is located next to the guest bath and we have one of those platform whirlpool tubs. So I was able open one of the panels and see the opening in the subfloor cut for the drain to that tub.

5/8 ply, not 3/4 ply.

Around the whirlpool tub it looked like the joist gap was 12" but when I ran a studfinder on the ceiling in the family room, it appears to be 16 o.c.

Couldn't figure out the joist span. Appears the joists run the length of the family room below the guest bath but that room is 20 feet long. So there is likely a beam up there somewhere because I can't imagine I have a 20 foot joist span.

Sorry I can't provide a bit more detail and I understand it's tough to get a real picture when you don't have a view of the rooms, etc.
 
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