bathroom tile floor subfloor

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Old 03-26-14, 06:54 PM
K
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bathroom tile floor subfloor

Hey all,

I've been reading up as much as I can here and elsewhere trying to ensure that my bathroom reno goes as planned. With that said, here are the details:

The bathroom is roughly 7x7 and includes a tub. My plan is to tile the floor space (~55x85) with 17x17 ceramic that the wife picked out.

Flooring appears to be 3/4 ply though I'll verify when I rip up the linoleum.
Joists are ~13ft long 2x10s, spaced 18in apart. It appears my deflection is OK for ceramic (though not stone, which we we've bought for another bathroom... perhaps another thread later).

I can add blocking if necessary; sistering joists would be a more difficult task, if even possible.

Am I good to go here? From threads here people suggest at least 1in of subfloor, though Ditra's website seems to suggest 3/4 single is sufficient for the job. If I need to add a second layer, what size, 3/8?

One thread someone mentioned leaving a gap of 1/8 between the second layer sheets for expansion in the field and 1/4 at the perimeter. Necessary?

I plan to follow suggestions of securing the perimeter every 4-6in and the field 6-8in; 2in screws sufficient?

Any another thoughts or advice I'll happily take; I'm comfortable doing most anything but flooring scares the heck outta me.

-Kevin
 
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Old 03-26-14, 08:20 PM
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You didn't mention putting a vapor barrier (I used roofing felt) down first, then cement board. Other than that, that's what I did over our bathroom floor with 3/4" plywood and have had no problems in the one year since I did it. Tiling the floor was relatively easy. I caulked the tile to shower base and covered the rest of the tile ends with baseboard. Be sure you undercut the door frame and slide the tile under it, then caulk any gaps.
 
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Old 03-27-14, 05:29 AM
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Those are pretty big tiles for such a small area, but if the Mrs. is happy, its all that matters. With large tile, your floor needs to be super flat, so keep that in mind as you prep. Under the linoleum will be 1/4" of plywood for smoothness, this needs to be removed as well. I always build up my floors to at least 1 1/4" - You would too if you had to put a warranty against your work. I believe if you read Ditra's instructions, 3/4" is said to be OK for a 16" OC floor structure, yours seems closer to 19" so I would not risk it. However, again, I always build my floors up. I would in your case add no less than 1/2" ply. Installing blocking helps stabilize a floor more than you can imagine.

Be prepared for unexpected things like possible water infiltration damage under the toilet or beside the tub, it is not uncommon. If your bath is standard shaped, plan for any sliver cuts (your tile will end up 3" shy of your 55" width) to be along the wall obscured by the toilet.
 
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Old 03-27-14, 05:51 AM
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Going need another layer of subfloor rated plywood, 3/8 would be the bare min. Do not have the seams line up with the seams below.
No need for a gap in the underlayment.
No need for a vapor barrier.
Make sure to use thin set under the tile board.
 
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Old 03-27-14, 08:23 AM
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I'm going to disagree with some of our friends above about a few things.

You should never install a cleavage membrane or vapor retarder between the subfloor and any underlayment when tiles are to be installed. This is especially important when installing a tile backer, (which you always should do), since the backer must be set into fresh thin set mortar in addition to fastening.

All wood underlayments are to be gapped 1/8" between sheets and 1/4" at the perimeter. That is standard procedure.

The concrete backers have their own gapping instructions that vary by manufacturer.

A single layer of 3/4" t&g subfloor is strong enough for ceramic tiles as long as it's installed correctly and still in good condition. Of course the more ply the better, 3/8" min. A few manufacturers even say it's ok for 24" oc. Yikes, I don't like that.

18" on center is unusual. Can you measure again and also measure the space between the joists? Maybe just a few are like that? How old is the house? Do you know the species and grade of the joists? Look for markings.

Jaz
 
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Old 03-28-14, 07:19 PM
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Ugh, my token expired and my post wasn't processed. argh.

Been busy demoing the bathroom, sorry for not responding sooner. Floor is in OK shape with some minor water staining around the toilet. Nothing rotten thankfully.

Joists are western pine #2, 16inOC. I was loopy when eyeballing them earlier.
Tiles are a bit big for my taste, but gorgeous. Plus they’re what the boss wants, so that’s the end of that. There was 1/8in ply under the lino which is now gone, though I have staples to pull yet.

Subfloor- I want to confirm my understanding of perimeter/field. Because the sheets are perpendicular to the joists, the perimeter is of each sheet, not the room, right? If the sheets are crossing the joists, how do I space the perimeter 4-6in and hit anything? Can I leave the seams open, or should I caulk them?

I ended up buying 3/8 to add. Aside from being on the lower end of what people suggested, as long as I secure both layers properly I should be fine? Also, is it ok (or expected even) to build up the entire floor, including under the tub? I bought PVC to redo the tub and toilet drains expecting this.

Ditra- Only to the tub (not under), right? To secure, modified thinset like Home Depots “VersaBond Fortified Thin-Set Mortar”? Any particular trowel to use? After setting, am I ok to walk on it? I’m planning to mud/sand/paint the room before tile and was planning to lay the ditra before that.

I think that was everything I had! Thanks all,
-Kevin
 
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Old 03-29-14, 08:21 AM
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All wood underlayments are to be gapped 1/8" between sheets and 1/4" at the perimeter. That is standard procedure.
Perimeter refers to the room in this instance.

If the sheets are crossing the joists, how do I space the perimeter 4-6in and hit anything?
Intentionally miss the joists on the top layer, mechanically fasten it to the first layer which should be screwed to the joists. Used exterior rated deck screws.

I’m planning to mud/sand/paint the room before tile and was planning to lay the ditra before that.
I would wait until all the mess is done before installing the ditra. There is no benefit to getting it in early.

No need to extend either ditra or the second layer under the tub.
 
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