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Old 04-02-2011, 03:41 PM   #1
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Sub-floor for tiling a bathroom


Hello all......I've read a bunch of the threads about sub-floors and the more I read the more semi-confused I get so I thought the best and quickest way was to tell you what I've got and what I plan to do.....hopefully, I'll provide enough detail so I can get a yay or nay to my approach to keep this short....

-1/2" ply is the original sub-floor
- joists 2 x 8 sixteen on centre
- two largest sections of this small bathroom layout - at its' longest stretch is 9 feet (5.5 feet of that is only 3 ft wide), another section is only 4 feet wide and 5.5 feet long
- quarter inch ply was added when the existing vinyl floor was installed
- I'll be using 13" tiles

My approach:
- remove quarter inch ply and vinyl
- add 1/2" exterior grade ply screwing to existing 1/2" ply and avoiding joists
- add either :
1/2" backerboard, thin-set and screwed to last layer of plywood with backer board screws, seams sealed with thin-set and fibreglass tape
or
Ditra or Ditra XL applied on top of thin-set to last layer of plywood, seams sealed using unmodified thin-set and Keri band

Q - do I have enough sub-floor support for the tile floor?
Q - is it just personal preference to use one of either cement backerboard or the Ditra?
Q -does backer board need to be primed?
Q - for the transition from the bathroom to the hallway - do transitions come in a variety of "transitions drops"? like 1/8", 1/4", 3/8", 1/2", etc?

Any and all help will be appreciated.....and if I missed any important details - please fill in the gaps (I'm just trying to bring together what I think I gathered in the other threads)

Thanks in advance,

Pat

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Old 04-02-2011, 04:56 PM   #2
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Sub-floor for tiling a bathroom


Hi Pat, welcome,

Overall, you're on the right track.

Quote:
1/2" ply is the original sub-floor
I'd be surprised if your sub is actually only 1/2" unless there was another layer of structural plywood over it at one time. No problem now since you're adding more now.

Quote:
joists 2 x 8 sixteen on centre
That's a typical layout, but what is the unsupported span of the joists? Do you know their species and grade?

Quote:
My approach:
Quote:
remove quarter inch ply and vinyl
Yes, you need to do that.

Quote:
add 1/2" exterior grade ply screwing to existing 1/2" ply and
avoiding joists


Yes right. Use floor screws, no drywall cheapo screws.


Quote:
add either :
1/2" backerboard, thin-set and screwed to last layer of plywood with backer board screws, seams sealed with thin-set and fibreglass tape
or
Ditra or Ditra XL applied on top of modified thin-set to last layer of plywood, seams sealed using unmodified thin-set and Keri band
Both products will work well. However, there's no need for 1/2" concrete backer, you can use the thinner version made for floors. I prefer Ditra. Waterproofing seams with Kerdi Band is not required for floors. You can if you want to, in which case I would flash Kerdi Band up the walls a few inches too.

Quote:
Q - do I have enough sub-floor support for the tile floor?
Q - is it just personal preference to use one of either cement backerboard or the Ditra?
Q -does backer board need to be primed?
Q - for the transition from the bathroom to the hallway - do transitions come in a variety of "transitions drops"? like 1/8", 1/4", 3/8", 1/2", etc?
1. yes
2. yes
3. No way
4. You can use various methods. Have you considered a marble threshold made specifically for that?

Jaz

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Old 04-03-2011, 02:13 PM   #3
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Sub-floor for tiling a bathroom


Thanks for the quick response JazMan......
The unsupported span is approx 11.5 feet and the joists I think are pine - grade unknown....
I'll definitely look into the marble transition you suggested.....
and I think I'll go with the Ditra - a little expensive up here in Ottawa but I have two bathrooms to do and I can probably sell the unused on Kijiji quick enough (if I decide to get the larger roll)......

Thanks again for all your help.....
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Old 04-04-2011, 01:14 PM   #4
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Sub-floor for tiling a bathroom


sorry to bug you again JazMan but I just got some new info........somewhere along the way I've ended up with 12" x 18" tiles that my wife picked out instead of the 13" that my wife and I picked out.....funny how that happens.......given the additional info I gave you concerning the span I'm just wondering if that changes any of your previous responses......

Thanks,

Pat
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Old 04-04-2011, 04:39 PM   #5
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Sub-floor for tiling a bathroom


Quote:
The unsupported span is approx 11.5 feet and the joists I think are pine - grade unknown....
Then I don't know either. 99% of all joists are some kind of pine. The species and grade is needed cuz at best you're in the "gray" zone. I think the only common species and grade that would be fairly safe is Southern Yellow Pine grade #2 or better. You'll want to consider sistering the joists or building a wall under the span, or ?

Get under there and figure it out. You should find stampings on at least some of them.

Quote:
I've ended up with 12" x 18" tiles that my wife picked out instead of the 13"
The floor deflection spec are the same, but the floor had better be real flat. Also be aware that all tiles have some warpage which shows more as they get larger.

You'll want to go with a 1/2" trowel and use medium bed mortar.

Jaz
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Old 04-17-2011, 03:02 PM   #6
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Sub-floor for tiling a bathroom


Hi JazMan.....sorry it took so long to get back with the joist details.....had a sudden death of a young (50) cousin in my wife's family and then several parental health issues than needed our attention.....

In answer to the type of joists I was only able to identify from the unfinished portion of my basement - so a huge assumption that the 2nd floor joists are one of the two listed below.
There were two types: one was stamped all along the length of the 2" side in red - W'nton (Winton?) Kiln Dried with a W enclosed in a circle and a logo that sorta looked like a stylized upper case QA with 122 No1 SPF S-DRY
The second type had LMA 6 5 (with the 6 over the 5) SPF S DRY 1

And if you don't mind, a couple of questions that popped up during my down time.....
1. When I install my second layer of plywood I leave 1/8 inch around the perimeter BUT do I also leave 1/8 between each piece I lay?
2. If 1. is yes, do I need to fill this gap with anything?
3. I bought Versabond for attaching the Ditra to the plywood - actually got it at a local hardware store and later noticed HD sold it - is this an acceptable product?
4. You mentioned for the floor tiles to use a medium bed mortar - being a rookie at this and up in Canada - can you name a product that you like/trust that I can google and look for a supplier up here
5. I'm also doing the tile wall around a bathtub and used Denshield as the backer (man that stuff is easy to work with). I've seen a couple of threads that mentioned the Flexbond product and wondered if this was an acceptable product for the tiling (if not, again could you suggest one that I could look for a supplier).

Sorry, that's more than a couple of questions
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Old 04-18-2011, 04:33 PM   #7
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Sub-floor for tiling a bathroom


Pat,

Sorry about the bad news.

Best I can decipher, you've got SPF grade #1. (Spruce-Pine-Fir). OK so, 2x8 @ 16" oc 11'6" span, SPF #1. You're either just barely OK or a bit shy of where I'd to see the deflection for ceramic tile. It'll most likely be OK if everything was done right and still in good condition. It would be nice if you could add sisters to the joists, or maybe a supporting wall under.

1. We generally says 1/4" around the perimeter and 1/8" between sheets.

2. Leave the perimeter open. The thin set bag should mention what to do with the 1/8" gaps. Some say fill, some say to apply a special tape or foam rod or even caulk the gap.

3. Versabond is good enough to install Ditra to plywood.

4. Medium Bed has different size silica (& maybe other) which helps prevent heavy tiles from sagging into the mortar, Generally if it says for Granite & Marble, it's medium bed. Both places should carry it. The only problem is that it's a modified mortar which Schluter does not approve using over Ditra. No big deal, I never expect anyone to guarantee the installation. Otherwise if available Ditraset is great stuff. I've never heard of anyone finding it in Canada though. It's sold under Hydroment & Durabond name, licensed by Schluter. The company is Bostik.

5. Flexbond is a premium mortar, so good. Even Versabond will work, but always best to get a better product I think. It's only money.

Jaz
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Last edited by JazMan; 04-18-2011 at 06:59 PM.
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Old 04-19-2011, 03:27 PM   #8
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Sub-floor for tiling a bathroom


Thanks heaps JazMan.........I recognize the medium bed mortar you mentioned........the Ditra book talks about long drying times (days and days) if I use modified......has that been your experience.......cuz I sorta need to have the bathroom functional by the end of the month.......
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Old 04-19-2011, 04:25 PM   #9
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Quote:
the Ditra book talks about long drying times (days and days) if I use modified
Before I was told I didn't have to use the $25 a bag modified over Ditra, I used high quality modifieds all the time since you're normally supposed to use modified thin set for porcelain tile. Never any sign of problems and many of those early installs where in my own neighborhood. Heck, I recall setting the last of the tiles on a Thursday, then grouting and replacing the refrigerator and stove on Friday.


Quote:
I sorta need to have the bathroom functional by the end of the month.


End of the month? The tile part is a 2 day job.

Jaz
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Old 04-20-2011, 12:18 PM   #10
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Sub-floor for tiling a bathroom


Ok so I'll go with the marble /granite mortar.....and yes, my comment about end of the month does sound weird.......what I was really getting at is I have out of towners coming in next weekend and I wanted to get the tiling and grouting out of the way this weekend (not much time to do things during the week) So if there was going to be the possibility of "many days" for the floor mortar to cure and harden the way the Ditra book was threatening - then time was going to get very tight......once again, a thousand thank-you's for your time and advice and I'll let you know how it turns out......
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Old 04-29-2011, 04:00 PM   #11
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Sub-floor for tiling a bathroom


Hi JazMan, I've been following your post to several folks about subfloor and joist spans, as I am also considering tile for our kitchen. I have 3/4" plywood as my subfloor, 2x10 (SPF 2) joists that are 16" o.c. - however the joists span 13"6". based on everything I read from you and others, tile would be out of the question unless I reinforce my floor, right? I do have access to the basement but building a wall in the middle of the basement to support the joists wouldn't be reasonable... or at least look weird. But what if I built the wall out a few feet to shorten the 13' length span to something like 10'? If the wall is not the right solution, then my only other option to nail 2x10s to each joist that supports the kitchen floor? Is that correct?

As I've been renovating my kitchen, I'm not just learning new things but also realizing how poorly my home was constructed back in '93 and how not to rely on the big box store advice.

So, I greatly appreciate all of the experience many of you share with us newbies!

*** I posted this question as a new thread ***


Last edited by twobyfour2; 04-30-2011 at 07:14 AM.
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