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Old 03-19-2014, 11:30 PM   #1
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Tiling bathroom floor - checking my plans


I’m planning to put tile on a 2nd story bathroom floor (currently carpeted – house built in 1997 with carpet in the bathroom). I’m still in planning stages, but want to check my plan so far.

I think the bathroom has only a subfloor, I’m assuming 3/4” plywood (at the top of the stairs, the subfloor is 3/4 inch), nailed 16” OC, not sure about joists but most likely, built to code (everything else in the house seems to at least meet code). Floor is very level (don’t seem to be any dips) & seems solid. Short of cutting a hole in it, I can’t check joist details.

Bathroom is L-shaped, 92 inches x 83 inches on long sides. Toilet at one end of L (L is 30” wide there), shower at other end of L (L is 34 1/2 inches wide there). See diagram below.

I’m going to use a porcelain (not ceramic) tile, probably 1 foot x 1 foot. I’ve thought about 1 foot x 2 foot, but am a little worried there may be a bigger risk of problems (cracking, grout issues) with the larger tile. Or am I worrying too much? If I use the 1 foot x 2 foot, how should they run? There’s a large-ish (4 foot x 4 foot) closet off of the 83” wall with a large window; entrance from the bedroom is through the door in the 92” wall. From what I’ve read, it would be best if they ran parallel to the 83” wall (so the 2 foot side is against the wall) – the claim is this would make the bathroom seem larger.

In another thread, it says with 24” between joists, you should put down (as an underlayment?) 3/8 or 1/2 inch subfloor rated plywood (above the existing subfloor). What’s the thinnest underlayment I could get away with? Adding any height to the floor is going to make it a higher than the bedroom.

That thread also mentions to install plywood so seams do not line up with joists below; nail every 4 inches on edges & 6-8 inches in field. Do I also install the plywood so the grain runs perpendicular to that of the subfloor below (I think I read that on here a few years ago), or does it not really matter in a space this small?

I did a bathroom(in another house) with Schluter-Ditra previously and was thinking I might use HardieBacker this time, but as I’ve looked at everything I’ll need to buy if I use HardieBacker, the difference in price is getting fairly small. The problem, as I recall, is that Schluter-Ditra specifies a kind of thinset for between the tile and the Ditra which doesn’t meet the specifications for porcelain tiles. What do people do in this case?

I used Mapei on the other bathroom (granite tile) – people on here said it was a good product. Any suggestions as to which Mapei products to use if I go with Ditra (I guess I can read the bags, too)? When people use porcelain tile, do they use the same product under the Ditra & between the tile & Ditra? (I need to re-read the Ditra instructions; I haven’t recently.)

The Ditra will cost me about $85 & if I can use the same thinset under it & between the Ditra & the tiles, that would be a nice bonus.

If I go with Hardie Backer, it has the following specifications:
Under HardieBacker:
  • Thinset under HardieBacker (per their instructions): Latex or acrylic modified thinset if finishing with tile (complying with ANSI A118.4)
  • Dry-set mortar (for use between subfloor and cement board only) (complying with ANSI A118.1)

(anyone have favorite brands for the things below?)
  • 2in. wide high-strength alkali-resistant glass fiber tape
  • Minimum 1-1/4in. long corrosion-resistant roofing nails
  • Minimum 1-1/4in. long No.8 x 0.375in. HD self drilling corrosion resistant ribbed waferhead screws
Attached Files
File Type: pdf BathroomFloor1.pdf (54.8 KB, 45 views)

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Old 03-20-2014, 09:04 PM   #2
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Tiling bathroom floor - checking my plans


To add to previous post:
The Schluter-Ditra installation manual (p. 6) seems to say I could install right over the 3/4 inch subfloor (no underlayment) if joists are 16 o.c. That assumes there won't be any flexing of the floor that would lead to cracks in tile or grout.
However, is it better to put in an underlayment to help some future person uninstall the tile (to avoid damage to subfloor). For that, 1/4 inch subfloor-grade plywood would work. But, does 3/8 inch subfloor-grade plywood add enough extra strength (just in case my floor isn't as strong as I think) that I should put in the thicker underlayment (and just live with the bathroom floor being higher than the adjoining bedroom floor)?

Mortar & thinset:
Schluter-Ditra says to use
  • Latex portland cement (p.c.) mortar (ANSI A118.11) under the SD orange
  • Unmodified thin-set mortar (ANSI A118.1) between the Ditra & Porcelain tile
Am I right in assuming I'm going to have to buy 2 different products (the latex portland cement is "modified", correct?). If anyone wants to recommend good products that correspond to the specs above, that would be nice.

Schluter-Ditra recommends using unmodified thin-set mortar under porcelain tile, which agrees with JazMan in this thread: What type of thinset for Porcelain tile?, so I am assuming it is the right choice.
From Schluter-Ditra installation manual:
Question: Can ceramic tile, including porcelain tile, be set on Schluter-DITRA with unmodified thin-set mortar? Answer: YES. In fact, we recommend it. Here's why: Portland cement-based unmodified thin-set mortars are dependent on the presence of moisture for hydration in order to gain strength. Since Schluter-DITRA is impervious, it does not deprive the mortar of its moisture. This allows the cement to properly hydrate, resulting in a strong, dense bond coat. In fact, after the mortar has reached final set (usually within 24 hours), unmodified thin-set mortars achieve higher strengths when cured in continually moist conditions.

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Old 03-20-2014, 10:22 PM   #3
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Tiling bathroom floor - checking my plans


Hi Lazz,

I see you're trying to get all your questions in at one time.

So you think the subfloor is 3/4" ply, 16" oc and
Quote:
Short of cutting a hole in it, I can’t check joist details.
No need to cut a hole to see. Drill a small hole someplace and stick a stiff wire or a dowel until it hits the ceiling below, then do some math. 2x8's are 7.25 - 2x10 are 9.25. Finally figure what the span is for the longest of these joists.

A single 3/4" ply, installed correctly and in good condition should be stiff enough for ceramic/porcelain. Of course adding more is always better.

Quote:
What’s the thinnest underlayment I could get away with? Adding any height to the floor is going to make it a higher than the bedroom.
Nothing thinner than 3/8". Years ago bathroom floors were often an inch or so higher. What kind of floor in the bedroom?

Quote:
Do I also install the plywood so the grain runs perpendicular to that of the subfloor below
No, underlayment goes perpendicular to the joists, so, the same as the subfloor. You gotta offset the seams from the subfloor of course.

Quote:
I did a bathroom(in another house) with Schluter-Ditra previously and was thinking I might use HardieBacker this time, but as I’ve looked at everything I’ll need to buy if I use HardieBacker, the difference in price is getting fairly small. The problem, as I recall, is that Schluter-Ditra specifies a kind of thinset for between the tile and the Ditra which doesn’t meet the specifications for porcelain tiles. What do people do in this case?
Why do you think it's a problem? It's not a problem. Just follow directions and I recommend you find a high quality unmod for the tiles. Report back with the choices available to you.

Quote:
When people use porcelain tile, do they use the same product under the Ditra & between the tile & Ditra?
It's very simple. You use the type of thin set that is compatible with the substrate. With ply or OSB you have to use modified mortar, there's no choice.

Quote:
Schluter-Ditra recommends using unmodified thin-set mortar under porcelain tile, which agrees with JazMan
Well dahhhh. Haven't you read my signature line below?

Jaz
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Old 03-21-2014, 03:51 AM   #4
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Tiling bathroom floor - checking my plans


Thanks JazMan, for all the info. Here's the info. you requested.

I drilled the hole (the experts know all the simple tricks).
  1. Subfloor is a full 3/4 inch thick.
  2. A wooden dowel went in 9 13/16 inches (before subtracting subfloor thickness); there seems to be something (like insulation?) in there. So it seems the joists are 2x10s (I didn't assess the width, although I guess I could if I drilled a couple of holes on either side of a joist).
  3. Joists run parallel to the 83 inch wall.

"What kind of floor in the bedroom?" It's carpet, & easy to remove. In front of the shower they put a 20" wide piece of particle board (it looks like that) & covered that with some kind of vinyl. I'll pull that out carefully; hopefully they did not glue it down. The subfloor is in excellent condition (I pulled up carpeting in the bedroom & hall last summer). I haven't pulled up the carpet in the bathroom yet, but I don't think there will be any nasty surprises (I have peeled it back a little at the doorway & in the corner under the sink).

Do you think it would be smart to put down the 3/8 inch underlayment, to make any future removal of the tile easier (& prevent subfloor damage)?

I live in a major metro area & have access to the blue store & orange store (and probably can get almost any unmodified thinset & modified mortar somewhere locally). I've used Mapei thinset & mortar before so I'd probably choose that unless someone advised otherwise (I've seen Mapei at the blue store so will probably get it there, if they have what I need).

Thanks again!
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Old 03-21-2014, 09:08 PM   #5
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Tiling bathroom floor - checking my plans


Are you sure you measured the subfloor or assuming? The 9 13/16" measurement would suggest the ply is thinner than 3/4". 2x10" are 9 1/4", see what I mean?

The carpet can be pulled back and shimmed if necessary. Adding 3/8" underlayment grade ply would be smart. You'll save some of the extra height by using Ditra instead of 1/4" tile backer. (is 5/16 or so total).

It's difficult to know what the big boxes in your area carry, they don't carry the same thin sets in all regions. Generally the orange place does not carry a decent unmodified mortar. Most do carry small rolls of Ditra though. In other words, they don't really care if your project comes out well or not. HD carries Custom Building products mortars and grouts.

Lowes is somewhat better, but some stores carry Mapei while others have Laticrete and a few Tec products.

Modified mortars are easy to find. Versabond at HD is good enough for Ditra on Ply, they also have several others. Lowes will have an entry level modified too, plus some better ones. Look for A118.11 for modified.

So, no decent unmodified at HD, the ones at Lowes aren't what I'd call premium. Lowes may carry one called Floor & Wall Tile mortar. It's probably decent, but not premium. Don't forget to see what the local tile shops carry. You want a premium that exceeds A118.1

Mapei makes Kerabond which is considered a high-end mortar. Laticrete makes a good one too, #370. One of the best is Ditraset, which is licensed by Schluter to Bostik/Hydroment, perfect for setting over Ditra and Kerdi.

Just stay away from the $6-9 a bag junk. Some of us suspect it's only slightly better than dirt.

Jaz
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Old 03-21-2014, 10:21 PM   #6
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Tiling bathroom floor - checking my plans


I pushed a dowel through the hole in the subfloor & it went in to 9 13/16 (I did it in 2 spots). I was thinking that the insulation (or whatever is in there - there's something in there; I just thought insulation was the most likely as it wasn't anything very solid) was adding a bit of thickness so that's why it came up about 3/16 short. The hole I drilled was just slightly bigger than the dowel so I couldn't really move it around. I'll see if I can anything thinner & try moving it around to see what's in there.

Thanks for the advice on the unmodified thinset & mortars. I'll call around; I'm sure I can find the good stuff. I'm not going to try to be cheap on those. I'll take this thread in with me.

For under the ditra, is this a decent option (from the blue store):
Mapei, 25-lbs Gray Powder Polymer-Modified Mortar
  • Polymer modified mortar
  • Can be used inside or outside
  • Smooth and creamy consistency for easy application
  • For use with porcelain and ceramic tile
  • Superior bond strength
  • Mix with water - no additive required
  • Exceeds ANSI A118.4 and ANSI A118.11 bond strength requirements
==========
For between the Ditra & tile, I'll use Kerabond (unless I go with Ditra-Set). You're right; it's not at the big box stores (according to their online inventory) but I'll call some tile stores. This is what I'm looking for, correct: http://www.mapei.it/public/US/produc...ond_TDS_EA.pdf (Kerabond: Premium Tile Mortar) - and I absolutely don't want the Kerabond/Keralastic, correct? (I saw that on the Mapei site).

Thanks again for all your help. It helps to have a specific product so when you're confronted with a dozen different bags of powder, you know exactly what you're looking for!

I found this site for interpreting Mapei manufacture date codes. It says to try to buy Kerabond that's been manufactured in the last 3 months.
http://no-curb.blogspot.com/2012/09/...i-setting.html

It looks like I may be able to get Ditra-set within 20 miles (Lumber Liquidators says they carry it, although I'm guessing I'll need to order it online for delivery). There is a tile shop about 16 miles away! If I use Ditra-Set, can I use it both under the Schluter-Ditra, as well as between the SD & the tile? It sounds like that, based on info. from the Bostik website:
Bostik® Ditra-Set™ is composed of select, proprietary chemicals, carefully graded aggregates, inorganic adhesion promoters and purified cements. It provides outstanding workability, excellent durability, significant leveling characteristics and superior bond strengths in interior and exterior applications when used in conjunction with the Schluter®-DITRA uncoupling membrane and Schluter®-KERDI waterproofing membrane. Use Bostik Ditra-Set™ to install the membranes over substrates approved by Schluter®-Systems and to set ceramic, porcelain, and stone tile over Schluter®-DITRA and Schluter®-KERDI.

Last edited by lazzlazz; 03-21-2014 at 10:50 PM.
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Old 03-21-2014, 10:55 PM   #7
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Tiling bathroom floor - checking my plans


I answered my own question about the Ditra-Set - I need to add either the Acrylic Admixture or Flex-a-lastic Admixture to it to use it under the Schluter-Ditra
http://www.bostik-us.com/sites/defau.../Ditra-Set.pdf

(The Lumber Liquidator website doesn't seem to know they are supposed to sell Ditra-Set (the Bostik website says they do); I'll call them to find out.)

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Old 03-21-2014, 11:30 PM   #8
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Tiling bathroom floor - checking my plans


The Bostik site usually just lists dealers that carry some of their stuff. No one has everything.

Yes, Ditraset to bond the tiles over Ditra or for over concrete floors. So, no, you need modified for over ply as you said.

That modified mortar at the blue store is fine for under Ditra.

My opinion; any A118.11 for over ply or OSB under Ditra is fine. Not every A118.1 is good enough to set tiles over Ditra or Kerdi. Even the cheapo unmods meet that spec.

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Old 03-23-2014, 01:43 AM   #9
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Tiling bathroom floor - checking my plans


I should nail underlayment to the existing subfloor using ring shank nails, correct? (In my OP, I mentioned another thread that said "nail every 4 inches on edges & 6-8 inches in field").

Jazman has already answered this question (how to fasten plywood to subfloor to even out floor height) but I am just verifying. L's only had 2" ring shank nails, which is too long for 3/4 subfloor + 3/8" underlayment, per the other thread. I'll see if somewhere else has 1 1/4" ones.

I've pulled off all the wood trim & have the floor down to the subfloor.

With raising the floor (3/8" underlayment, + Ditra, + tile), the tile is going to be up above the bottom edge of the wall board. Should I use something like the Schluter Schiene Edge Protection trim (http://www.schluter.com/2171.aspx) along the walls? There shouldn't be a lot of water on the floor, but it is a bathroom - would a trim help (a little) to keep any water from getting to the wall board - especially if I chose one that was a tiny bit (1/16") higher than the tile ? I was going to reinstall the wood trim once the tile is in, so the edge trim would be hidden by the wood trim.

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Old 03-23-2014, 02:46 AM   #10
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I was trying to figure out how to handle the expansion gap - I'll have just one between underlayment plywood pieces.

Purpose of gaps between sheets of plywood?
Jazman (2009): "The gaps are for expansion, and most, (if not all), thinset manufacturers want you to fill with thinset as you install the tiles. This will not cause the floor to tent unless the floor floods and stays wet for some time, and the tiles were bonded direct to the plywood. Which of course is not a recommended method for floors that can get some water now and then."

Assuming nothing's changed: I shouldn't worry about thinset getting in the gap & no need to tape the gap (as has at times been proposed in various discussions). It seems that if you taped, the mortar over the tape wouldn't be bonded to anything (other than the tape).
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Old 03-23-2014, 11:19 AM   #11
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The fastening schedule is dependent on the thickness of the underlayment, the thinner, the more needed. 4" and 5-6" is good for 3/8".

You don't use metal edgings against base molding or at drywall, not necessary. They're used at doorways and other exposed ends. Those molding will not waterproof the edges anyway, with the exception of some of the Dilex pieces. If you wanna waterproof the floor/wall joint, apply Kerdi Band over all Ditra seams and where Ditra meets the wall inside corner, then your tile base. Of course the room still won't be watertight like a shower, but bathroom floors don't need that. You may want to reconsider installing wood base moldings in a full bathroom.

The expansion gap in the subfloor and underlayment; Read what the thin set manufacturer wants. Most want you to fill that gap. Some would like you to apply a thin bond-breaker tape over the crack, (not fiberglass mesh seam tape). Some people have decided to just caulk it if the answer is to not fill it.

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Old 03-23-2014, 06:42 PM   #12
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Tiling bathroom floor - checking my plans


For Ceramic Tile Mortar (under Ditra), Mapei says "EXPANSION AND CONTROL JOINTS Provide for expansion and control joints as specified per TCNA Detail EJ171. Do not cover expansion joints with mortar." http://www.mapei.it/public/COM/produ...r_EN_LoRes.pdf

I did find one page of the 2007 version of EJ171 at www.johnbridge.com/vbulletin/attachment.php?attachmentid=40478

After reading that, I'm thinking that where my 2 pieces of plywood come together is not the kind of expansion joint they're talking about - in other words, I misused the term "expansion joint". My bathroom isn't big enough to need the expansion joints that are required by the size of the tiled area. I just have 2 pieces of plywood that meet each other.

I found the bond breaker tape online so I understand what you're talking about. I can use that over the gap.

About the "wood" trim: actually, most of it is MDF but there were 2 pieces that were painted wood (maybe they ran out of MDF?). I'll probably put it back in for now, since it came out of there, but if there are any problems, I'll replace it. It looked fine when it came out, other than needing to be painted before going back up. Thanks again.
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Old 03-23-2014, 07:29 PM   #13
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Tiling bathroom floor - checking my plans


The instructions on the bag of mapei refers to expansion and control joints of slabs and concrete/block walls. Although they are also required in the tilework over wooden substrates too when the size is large enough or under certain conditions such as direct sunlight.

The only expansion gap you should leave is in the perimeter.

It's your choice if you'd rather have wood base and shoe, or tile base to match the floor. I doubt there's a code you'd have to deal with. Generally I think ceramic base is best with ceramic floors. Don't have to worry so much about wiping with a damp rag.

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Old 03-23-2014, 07:55 PM   #14
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Thanks again. I have the 1/4" around the edges of the plywood.

I was reading a little more about what to do with the gaps between pieces of plywood; it seems there is absolutely no agreement on what to do there! (http://www.johnbridge.com/vbulletin/...ad.php?t=94786)
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Old 03-23-2014, 08:06 PM   #15
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Tiling bathroom floor - checking my plans


That's right, there's no agreement amongst us tile guys. That's why I said to do what the thin set manufacturer wants.

However, once the plywood subfloor has dried out and stays that way, there shouldn't be much expansion beyond the ability of the modified mortar to handle. The only exception may be if there's a crawl space and the under space is not treated and conditioned as it should be, including under floor insulation/vapor barrier.

Jaz

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