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Old 11-23-2014, 11:03 AM   #1
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Help with sublfoor materials and thickness


I am re-tiling my bathroom floor and need help with the subfloor. I haven't torn anything up yet, just planning ahead for Christmas project.

So from what I can see, this is what I currently have. House built 1965.
1/4" tile
5/8" plywood
3/4" diagonal tong and groove boards.
8x1.5" solid wood joists(not sure on wood, probably Douglas fir) 12" spacing though possibly doubled up under the bathroom floor. Tough to see as basement is finished. Span is about 12 feet.

So, my question is my new tile is 3/8" thick (24"x12"), so just replacing the tile will leave a height difference between the hardwood floor outside the bathroom. I'd like to keep it level. What can I do with the subfloor to reduce thickness?

It's only about 30 sqft so I'm OK with using more expensive material like Ditra.

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Old 11-23-2014, 04:52 PM   #2
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Help with sublfoor materials and thickness


Hi Fuzz,

Are you saying that floor is original to 1965? Are you positive the tiles are bonded to the ⅝" ply?

Do the joists actually measure 2x8" or do they really measure 1.5 x 7 "? Is there at least part of the ceiling which is not finished, furnace room, storage? What size are the diagonal boards? The span should be about 12', can you be more specific?

I can't give you my final opinion until I know what you've got and the condition of the subfloor, and more info about the joists.

Jaz

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Old 11-23-2014, 05:13 PM   #3
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Help with sublfoor materials and thickness


The slats are original. The ply may have been put down later, I know the tiles were put in about 8 years ago(just before I bought the place) and look to be bonded directly to the ply.

Joists are 1.5x7 1/4. Diagonal boards are about 3" wide, 3/4" thick, not sure how long. Joists and boards all look to be in very good condition. Most of the ceiling under the bathroom is finished, just one gap between joists exposed.

The 12' joist span is from the side of the house on the foundation to a steel crossbeam that bisects the house. Its basically a 1000sqft bungalow with a beam across the middle. The bathroom runs from one side of the house to the middle beam. From what I can tell the house was built very well with top quality materials for its day, it just had a crappy reno 8 years ago.
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Old 11-23-2014, 10:43 PM   #4
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Help with sublfoor materials and thickness


Tiles directly on plywood isn't a very good method, but it can work. Sounds like you wanna remove just the tiles and re-tile over the ⅝". You'll know better once you start ripping the tiles, sometimes the ply gets damaged.

Otherwise you might have to also remove the underlayment and replace. Technically you could go with ", then use Ditra or concrete backer. But I recommend using the thickest possible, so try to stay with ⅝". Use good quality underlayment grade, no cheapo CDX stuff.

A slight difference it height can easily be addressed with thresholds, even " or so is manageable. Looks like the bathroom will be ⅜ to " higher than the hardwood.

If the joists are Doug Fir #2 from the '60's in excellent condition you are very close to the min. specs. Southern Pine or better grades will be better. Either way you're probably ok. How does the floor feel? Check it after you remove the tiles.

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Old 11-23-2014, 10:59 PM   #5
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Help with sublfoor materials and thickness


I'm fine with pulling up the plywood and laying new stuff. I was hoping I could go to 1/2" ply and Ditra at most, I'd really rather not have any height transition. The floor feels very solid, current tile is 12"x12" and no cracks.

If I had to do some sort of transition how is it done?
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Old 11-23-2014, 11:45 PM   #6
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Help with sublfoor materials and thickness


Assuming you do have ⅝" ply and you replace it with " + ditra, you'll be at zero gain, the same height. The only difference will be the extra ⅛" or so of the new tiles. This might work well. I say might cuz of the thinner " ply. If you went with ⅝" instead you'd be about " higher.

You can have a marble threshold made with a bevel to transition down to the hardwood. You'd have to play with the thickness of the ply under the marble though to make it flush or do as in the old days and have the threshold about " higher where it meets the tiles. Bathrooms floors were always higher than the hall plus the marble was set higher than the tiles to create a lip to theoretically hold water in case of a small flood.

You could also eliminate the threshold and use a small molding like a shoe molding to cover the edge. Again, you'll know better once you know which way you're going.

Jaz

This picture does not reflect your situation except if you can imagine wood instead of carpeting with a shoe molding to match the wood to cover the transition.
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Old 11-24-2014, 08:17 AM   #7
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Help with sublfoor materials and thickness


Eeek, that looks like a stubbed toe at 3am waiting to happen! I was wondering about using a transition strip, something like this:
http://www.homedepot.com/p/TrafficMA...8?N=5yc1vZbnar

Also are you saying 1/2" plywood with the ditra would be a strong enough substrate? That would be good news. I could deal with 1/8" transition.
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Old 11-24-2014, 08:31 AM   #8
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Help with sublfoor materials and thickness


Any grout or tile cracking currently?
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Old 11-24-2014, 08:36 AM   #9
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It all looks to be fine. I can't see the stuff under the vanity though. There is one cracked tile, but given the crack pattern and a chip, its most likely from a dropped item. Given how poor of a tile job was done(no straight lines, uneven spacing, ugly grouting) the fact that there is no cracking despite the poor workmanship shows the subfloor is probably pretty solid.

If I do pull up the 5/8 and lay 1/2 I guess the only issue may be if the ply is glued to the subfloor...The ply looks pretty old, so I suspect it wasn't layed 8 years ago when this bozo put the tile in.
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Old 11-24-2014, 12:46 PM   #10
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Help with sublfoor materials and thickness


Ditra wouldn't be a bad idea, it'll help with your floor height issues. As much as a flush transition is nice, I wouldn't give that up for going skimpy on the subfloor. As has been mentioned before, the transitions really aren't that bad and if you look around more often then not, you'll see a lot of them.
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Old 11-24-2014, 09:49 PM   #11
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Help with sublfoor materials and thickness


Thanks guys. I was looking at the ditra info pdf here:
http://www.schluter.com/media/ditra-...v=201407190607
on page 6 it says :


Requirements
maximum spacing of joists, I-joists, or floor trusses is 16"(406 mm) o.c.

minimum subfloor thickness – 19/32", 5/8" nom.(16 mm) tongue-and-groove with 1/8" (3 mm) gap between sheets

Does that mean you can install the Ditra directly over the tongue and groove? I'm not sure I understand what they are saying.
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Old 11-25-2014, 12:19 AM   #12
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Help with sublfoor materials and thickness


Quote:
Originally Posted by Fuzz
minimum subfloor thickness 19/32", 5/8" nom.(16 mm) tongue-and-groove with 1/8" (3 mm) gap between sheets

Does that mean you can install the Ditra directly over the tongue and groove? I'm not sure I understand what they are saying.
No it doesn't. Please read the paragraph again. It's describing the subfloor as; single layer OSB or plywood subfloor. You have a plank subfloor, not plywood or OSB. You can't install Ditra or concrete backer over planks.

In post #7 you mentioned the carpet bar. I think that would be a bad move, looks too cheap IMO, and it's for carpeting.

As for the toe stubber in the pic. Your situation is different, but in the case of carpeting it should/could be shimmed to meet the tiles better.

Jaz
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Old 11-25-2014, 08:36 AM   #13
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Help with sublfoor materials and thickness


Ok, that makes sense. I figured I was reading it wrong, that's why I asked!

As for the carpet bar, I guess I didn't mean that one specifically, just some sort of transition strip that could be angled since it will be a small height difference, and an gentle slope seams better than a hard edge...
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Old 11-25-2014, 10:51 PM   #14
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Once you know the height difference you will know better what to use. It also depends if the tiles are ending under the door or if the jamb/threshold area will be tiled, as in the pic above. Use a marble threshold or a wood reducer or saddle.

Jaz

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