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Thread: Bathtub installation -- order of installation (end pony wall, tub, heated floor)?

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    DIY Senior Member jch's Avatar
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    Question Bathtub installation -- order of installation (end pony wall, tub, heated floor)?

    Here is my gutted bathroom. I have a left-hand-drain Kohler Villager cast iron tub (with apron) that I want to install along the far wall (i.e. along the wall that has exposed insulation):

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    The tub is 60" long and the available space is 78" (with a downward-sloping ceiling).

    Questions:
    1) Do I install the tub (on a ledger board) *before* building a pony wall along the non-drain end of the tub? Or do I build the short (20" 2x6) pony wall first?

    2) I plan on installing a heated tile floor. Because the room has some funny angles (not visible in the picture), I was going to run my own heating cables and then pour Self-Leveling Cement. Do I run the cables and pour the whole floor *before* installing the tub? Or do I put in the tub first and then pour SLC on the remaining area? (The heating cable would only be under the exposed tiles, not the tub). My concern is the joint between the tub & SLC, and the reduction of tub-height -- it's only 14" to start with.

    This is my first bathroom reno, so I'd appreciate any tips.

    Thanks!
    .../j
    Last edited by jch; 07-10-2011 at 01:04 PM.
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    - John

  2. #2
    Forum Admin, Expert Plumber Terry's Avatar
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    In this case you could do it either way, either set the tub first or install the pony wall first.

    When we install a tub, we put a 2x4 flat; if that is the right height of the concrete pour, and then pour up to that. I don't like setting a heavy tub on concrete if it's that thin. The 2x4 makes a nice resting place for the apron.

    Then you can finish tile up to the tub.

    http://www.terrylove.com/forums/show...-Cast-Iron-Tub
    Last edited by Terry; 07-10-2011 at 01:47 PM.

  3. #3
    DIY Senior Member jch's Avatar
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    Thanks for the speedy reply Terry!

    I'm hoping that the concrete won't need to be that thick (for headroom). I was hoping for more like 1/4 - 3/8" thick SLC if possible. Or am I dreaming?

    And does the wooden apron support stick out in front of the apron? Or do you try to install it flush with the front of the apron?

    Thanks!
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    Forum Admin, Expert Plumber Terry's Avatar
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    I haven't installed the electric heating mats, but they may go under the tile without doing too much.
    If that is the case, just set the tub on the plywood.

    You only support at the back wall. One stringer does it.

  5. #5
    DIY Senior Member jch's Avatar
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    The more I think about it, the more I think that I'd better do the SLC last. I *know* I'd end up dropping something on it while wrestling a cast iron tub around the room...

    So how does this sound then:
    1) Build 2x6 pony wall along non-drain end of tub
    2) Install wooden 1x4(?) along floor where tub apron will sit
    3) Install 1x4 or 2x4 ledger along wall (depending on clearance of tub), measuring up from top edge of apron support
    4) Skid/rotate tub into place using instructions here: http://www.terrylove.com/forums/show...-Cast-Iron-Tub
    5) Install in-floor heating cable
    6) Pour SLC to bury cable
    7) Install Schluter Ditra anti-fracture membrane on top of SLC with thinset
    8) Install floor tiles

    Sound good??
    Last edited by jch; 07-10-2011 at 01:50 PM. Reason: typo
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    Forum Admin, Expert Plumber Terry's Avatar
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    You have enough room there that you may be able to just slide the tub in.

    But either way, so far, so good. That looks close enough for a plan.

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    DIY Senior Member jch's Avatar
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    Mapei said that the hairline cracks are probably not all the way through the pour--just on the surface. There is definitely no visible change in crack width when I bounce my full body weight near them. My guess is that the hairline cracks are from having slightly too much water in the mix--I used the upper end of the prescribed range but it was a super humid day. The cracks didn't appear until day 3--long after most pros would've started tiling.

    That said, I agree that a crack-isolation layer would be wise. Ditra is available locally by the foot so I think I'll go with that.

    Question: Which specific thinset should I use to attach the Ditra to the SLC? Over wood I know I would use a modified thinset, but over SLC I'm not so sure. Locally I can get Mapei and Ardex products. Just not sure which specific version is appropriate.

    Thanks again for your help.
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    Retired Defense Industry Engineer jadnashua's Avatar
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    If you don't have it, download the Ditra handbook from the www.schluter.com website. It gives you all you need to know about installing it over all acceptable substrates. It's a good reference to have.

    From page 9:
    Setting and Grouting Materials
    Unmodified thin-set mortar – ANSI A118.1

    You want a premium quality dryset mortar, not the ecomony price leader in the line.



    Jim DeBruycker
    Important note - I'm not a pro
    Retired Defense Industry Engineer; Schluter 2.5-day Workshop Completed 2013, 2014

  9. #9
    ACO Shower Drain Sales johnfrwhipple's Avatar
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    You have gone this far with the Mapei line of materials. Why not use their Kerabond setting material. If you buy some Keralastic you can mix up some modified thin set for your tile install over the Aqua Defence.

    http://www.mapei.com/public/CA/produ...tic_TDS_EA.pdf

    Using a plain non-modifed thin-set it is important to note that they take a longer time to get a good bite. Do not set the Ditra and then tile the same day. Any checking of coverage will cause a suction effect on the Ditra and could cause a bond failure as the Ditra is pulled off the self leveller.

    Better be safe and set the Ditra and then let it cure out a good couple days. I've layed a lot of Ditra with modified setting material and do so at my own risk, knowing that Schluter does not allow or warranty this work without written permission from head office. If your in a hurry and I don't think you are then finsih the floor with Ardex setting materials from setting the tile to grouting - this will allow you to use premium modifed thin sets and even double your warranty if you use the right products.

    Kerabond is a great non-modifed thinset. I spoke with a top tech at Schluter some time back and he suggested using 'White' non-modifed thinset. I can not remember the entire conversation but I believe that white thinset is a better quality than grey when comparing apples to apples. I have followed this advice and when working with non-modifed thinsets prefer the white for my bonding applications.

    Kerabond is sold in white and gray. Next time I see my rep I'll ask him if he knows if one is stronger or better than the other.

    Good luck.

    JW


    jfrwhipple@gmail.com - www-no-curb.com - 604 506 6792

    Always get construction advice double checked by your local city hall. Flood Test Every Shower - Every Time.

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    Retired Defense Industry Engineer jadnashua's Avatar
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    In a class I went to, they said that the reason white thinset was more expensive (often a buck or two a bag) is that to get it white, they have to use cleaner, higher quality sand and components. Now, I don't know if it is actually stronger (never compared the tech data sheets, and don't know if they even are different), but by using cleaner, better sorted materials, it likely is. Unless you are planning something like black grout, white thinset tends to work quite well for most anything.
    Jim DeBruycker
    Important note - I'm not a pro
    Retired Defense Industry Engineer; Schluter 2.5-day Workshop Completed 2013, 2014

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    ACO Shower Drain Sales johnfrwhipple's Avatar
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    Jim I also think it has something to do with "Fly Ash".

    It appears that the cement industry is using more and more of this and it's hard to know what the Portland ratio is in relation to "Fly Ash" ratio. I have heard in my Mapei training classes that this is generating huge problems on commercial projects and Mapei has recommended to me that I inquire on the cement type and mix ratio for any commercial project.

    I'm not sure if companies like Laticrete, Custom, Mapei or the like use any "Fly Ash" in their production or if they even know it's included perhaps with a portland cement order.


    jfrwhipple@gmail.com - www-no-curb.com - 604 506 6792

    Always get construction advice double checked by your local city hall. Flood Test Every Shower - Every Time.

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    DIY Senior Member jch's Avatar
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    Thanks. Turns out the data sheet I need is the one that doesn't use Keralastic as an additive, just Kerabond plus water:
    http://www.mapei.com/public/CA/produ...ond_TDS_EA.pdf

    Based on what you've both said, I'll get some Ditra and a bag of Kerabond White (for both over and underneath the Ditra).

    Trowels:
    - How does 1/4"x1/4" square trowel sound for using to bond the Ditra to the SLC with Kerabond?
    - What size trowel do I use on top of the Ditra when installing my 12" x 24" porcelain tiles? 1/2" U-notch?

    How do I know if I'm using the right sized trowel? i.e. how do I know when I've got the wrong size during the job?? (V, square, U-notch)?

    Thanks!
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    - John

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    DIY Senior Member jch's Avatar
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    I took out the toilet drain stub tonight and then could see that the cracks go all the way through the SLC.

    Also, now that it's been 10 days, no more new cracks have appeared. Now I can see a pattern--they're approximately over top of the structural members--joists and blocking. Which tells me the 3/4" T&G exterior ply is "hammoking" between joists.

    Regardless, the SLC is firmly bonded to it.

    Put down the Ditra tonight--using their 4.5mm square notch trowel--worked really well. Thanks for all the advice.

    For laying the 12x24" tiles, do I make all my cuts before I start thinsetting them down? Or do you recommend I cut as I go??

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    Retired Defense Industry Engineer jadnashua's Avatar
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    Gluing the subfloor to the joists when nailing or screwing it down can help a lot with this. What you see is one reason why they require TWO layers of ply for natural stone installations. The edge of a board will act like a lever when there's deflection between the joists. That's also why you don't line up the joints on sheets - the top layer should be 1/4-span past a joist. This can also happen if the subfloor is not installed perpendicular to the joists, as it is much stronger across the joists due to the face grain. If your joist spacing is within specs, you'll probably be okay. Ditra can help if the subfloor is within specs. This is one reason a lot of pros like to install a second layer of ply regardless of whether it is for ceramic or stone. INdustry standards call for a minimum of 5/8" ply on 16"oc joists, but again, most people don't like the minimum, as it leaves little margin for error.

    As long as there's no vertical displacement on the cracks, you should be okay.

    Precutting sort of depends. Any little miscalculation can be exagerated when setting. On a small room, probably not a big deal - it can be huge on a large install. Off by 1/32" over a row of 32 tile, is an inch, which would likely be unacceptable. But, if you have layout lines and are constantly correcting as you go, it's not as big a deal. Depends on how many, if any, critical things you have in the middle. If it is a clear, unobstructed job, since you need a gap at the edges, being off a little isn't a big issue as long as the baseboard will cover it.
    Last edited by jadnashua; 06-27-2012 at 05:36 AM.
    Jim DeBruycker
    Important note - I'm not a pro
    Retired Defense Industry Engineer; Schluter 2.5-day Workshop Completed 2013, 2014

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    DIY Senior Member jch's Avatar
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    That's what's puzzling about this.

    - I glued and screwed the 3/4" exterior t&g ply to the joists and the blocking using deck screws and construction adhesive (PL400)
    - I ran the ply's face grain perpendicular to the joists (see photos earlier in thread)
    - the cracks are not at the plywood joints--instead they seem to roughly follow all the joists and blocking
    - I have a layer of 1/2" ply that I was about to install over the 3/4" (using the staggered offset you describe) but the TCNA and Ditra manuals convinced me that it wasn't necessary. In hindsight I should've eaten the extra headroom and used it. I won't know until the tile is installed over the Ditra whether this was a critical error.



    On another note, I mixed 1/3 bag of thinset when putting down the Ditra and it wasn't enough. Had to stop part way through and mix more (which is much harder than mixing entire bags).

    Trying to figure out whether I should continue to mix small batches and cut tiles as i go when laying the tile or whether I should precut a bunch so I can lay a lot at once.

    Would it work better to lay the uncut field tiles first in one big batch, then go back and do the cuts for the perimeter tiles and then lay them as a group???
    Last edited by jch; 06-27-2012 at 07:46 AM.
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