Durock Installation Question

Discussion in 'Shower & Bathtub Forum & Blog' started by Thomas K, Feb 9, 2021.

  1. Thomas K

    Thomas K Member

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    Hi! I'm about to install Kohler Bellwether cast iron tub (with ledger board :) ). I am planning on installing 1/2" Durock on the walls and using RedGard to waterproof the board. My question is how do I transition from the Durock to the tub? I think I'm supposed to install the Durock over the tub lip to within 1/4" of tub surface, extend tile down another 1/8" toward tub, and seal gap with pure silicone. Or can I just install Durock on the wall and extend the tile down past Durock and caulk?

    Thanks for any replies!

    -Thomas
     
    Last edited: Feb 9, 2021
  2. WorthFlorida

    WorthFlorida The wife is still training me.

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    Do what the manufacture instructions reads. If you're worried about a little flare out of the Durock, cut a little chamfer on the back edge and let it overlap the tub lip. I would not use 100% silicone but a siliconized caulk with a miroban. It is easier to apply and smooth out. If you ever had to it is also easier to cutout for a redo.
     
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  4. Thomas K

    Thomas K Member

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    familyhandyman.com/article/tile-installation-backer-board-around-a-bathtub/

    I tried to make a link, but copy and paste will work. I'm asking if this approach will work with cast iron tub.
     
  5. WorthFlorida

    WorthFlorida The wife is still training me.

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    I can see why, Durock is very stiff with no give. With water and a person on the tub there can be some settling and springs back up when empty and even seasonal humidity changes there can be movement. CI is does not flex but the floor can if it is on anything but concrete. The slightest movement can crack grout or tile. The gap also prevents any water from being wicked up by the backer board.

    I personally prefer an overlap that makes it nearly 100% leak proof behind the tub. Most water intrusion around a tub is through the grout and RedGard is a perfect product to prevent it. This JohnBridge site is the go to site for tiling questions and how to's. https://www.johnbridge.com/
     
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  6. Thomas K

    Thomas K Member

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    Since I will be installing the cement board horizontally rather than vertically, will the chamfered edge be sufficient to clear the tub lip? I know the cement board doesn't need to touch the tub anywhere, as you stated, because it can wick water up the wall.
     
  7. wwhitney

    wwhitney Well-Known Member

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    Best practice is to fur out the wall framing so that the backside of the cement board will be in plane with the face of the tub flange. Then the cement board can be flat and hang down over the flange, stopping a 1/4" above the tub deck. The cement board gets a surface waterproofing, and the 1/4" gap gets silicone caulk. Bear in mind that the entire shower should be waterproof before any tile or grout are installed; they are just a water resistant wear layer.

    Cheers, Wayne
     
  8. kreemoweet

    kreemoweet In the Trades

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    I doubt very much you will be able to "chamfer" an edge of that kind of cement board. Trying to do so will likely just make a mess of the edge.
     
  9. WorthFlorida

    WorthFlorida The wife is still training me.

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    Using paint sticks is usually the perfect thickness to fur out the studs.
     
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  10. WorthFlorida

    WorthFlorida The wife is still training me.

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    It doesn't matter, but as others has suggested chamfered the edges could be difficult. Take a piece and with a new blade in the utility knife and a pair of gloves and try it. If it doesn't work then fur out the studs as Wayne suggest. HD does sell paint sticks in pack of ten for a dollar and 5 gallon pail stir stick in a pack of three for a buck. The 5 gallon size is thicker.
    If this is getting to complicated nothing wrong with going according to the installation instructions from the handyman article where the backer board stops just before the tile rim edge and then silicone a bead and tile over it.
     
  11. wwhitney

    wwhitney Well-Known Member

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    Disagree. That's a vulnerable joint, and silicone alone may not be sufficient in the long run. A shingled overlap plus silicone is a better choice.

    Cheers, Wayne
     
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  12. Thomas K

    Thomas K Member

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    I could shim out the walls, but the 1/2" Durock will be sticking out past the drywall. I also have a Wen electric hand planer. I thought about planing the studs a little to give me the needed spacing, but I would be planing on load-bearing studs and I don't think that would be a good thing. Is method to drop cement board to within 1/4" of tub surface, caulk gap, two coats of RedGard on cement board, drop first row of tile down to 1/8" of tub surface and caulk second gap between tile and tub? Tub going in is Kohler Bellwether K-837-0.

    I got caught with my pants down. :( . Sold house we're living in now, and bathroom in purchased house is nowhere near finished. Have five weeks to sort this out before closing.
     
    Last edited: Feb 14, 2021
  13. wwhitney

    wwhitney Well-Known Member

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    Yeah, that's always an issue. Sometimes you can just fur out the whole wall. And/or use 5/8" sheetrock. Otherwise, the tile should extend beyond the wet area, with a tub leg going down to the floor. So depending on how much the two surfaces are out of plane, you might need a quarter round tile to terminate against the drywall, or a border of thicker bullnose tile.

    For the back wall, and one of the short walls, planing the studs to recess the tub is absolutely an option. You'd want the edge of the stud to be in plane with the face of the tub flange. But if the other short wall is preexisting, that will mean shimming that wall even more. The allowable notch in a bearing stud is 25%, so planing them 1/4" or 3/8" would be no problem.

    Yes, with the understanding that the cement board laps over the tub flange, so that's to within 1/4" of the horizontal tub deck. And use of a wet film gauge when applying RedGard is recommended.

    [If you're not fixed on Durock, you might consider something like Johns Mansville Goboard, or Kerdiboard, instead. Being foam boards, you could fairly easily rabbet the bottom edge to sit over the bathtub tile flange. Whatever you use, read and follow the manufacturer's directions. Unfortunately, the Durock directions I found did not address how to handle a bathtub tile flange. Nor did the RedGard directions I found.]

    Have you checked with the buyers to see if their schedule is flexible, and whether they'd be willing to rent back to you for 2-4 weeks? (Or postpone closing, but I assume a rent back would be generally be preferable to both parties.)

    Cheers, Wayne
     
    Last edited: Feb 14, 2021
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  14. Thomas K

    Thomas K Member

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    Okay. Looks like I may need to add 1/4" shims behind the Durock to bring it out over the edge of the tub flange, or plane it. The idea of using 5/8" drywall didn't even occur to me. I was planning to tile only out to edge of tub, with drywall beyond that. I was planning to build a 36" wall behind tub for stackable washer/dryer area, so if tile went to edge of tub, it would be 30" of tile, and 6" of drywall beyond that. Tiles being used are 6" x 12".
     
    Last edited: Feb 14, 2021
  15. wwhitney

    wwhitney Well-Known Member

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    See my previous post again, as I kept editing it.

    Having the vertical edge of the tile at least a couple inches past the tub apron is definitely best practice.

    Cheers, Wayne
     
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  16. Thomas K

    Thomas K Member

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    Would that entail bringing the tile vertically down the side of the tub as well? Can you show me a photo example?

    This will definitely mean cutting tile somewhere to make that extra 2" fit.
     
  17. wwhitney

    wwhitney Well-Known Member

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  18. Thomas K

    Thomas K Member

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    Nice! Just to be curious, I put in a pocket door near tub. If I tiled all the way out to door, I'd have to put the door trim over the tile. Wondering how that would look, or if the trim is even needed. It's about 6" from edge of tub to door opening.
     
  19. wwhitney

    wwhitney Well-Known Member

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    How wide is your door trim? You probably want to tile up to the trim, with a caulk joint between tile and trim. You definitely want the face of the trim proud of the face of the tile.

    Applying trim over the tile would be trouble, because there will be no tile on the other side, so you'd need thinner trim to go over the tile. I have a similar situation on a tub surround I need to redo (no tub leg), but I have a wide trim with less than 1" between the trim and tub. So I'm going to have to rabbet the wood trim to go over the tile.

    Cheers, Wayne
     
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  20. Thomas K

    Thomas K Member

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    I cleaned my work area up well this afternoon, and will be posting some photos shortly. If I remember correctly, door trim is 2". Think I'll notch the studs at long side of tub. I thought I'd have to notch them all the way down, but looks like only 1- 1 1/4" for tub to clear.
     
    Last edited: Feb 14, 2021
  21. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

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    It all depends on the tile you choose and how tall the tiling flange of the tub is. Using RedGard, to seal to the tub, you could use their tape. An easier system solution would be to forget the Durock and use something like Wediboard or KerdiBoard, or even plain drywall and Kerdi over it. For either of the Kerdi products, Schluter has videos on how to do this on their website.

    if you use the Durock, and buy the RedGard, some of the other choices end up about the same cost, but are lots easier to carry home, cut, and install.

    As long as the tile is more than 50% supported on the Durock, the bottom can cantilever over the edge. You aren't going to be walking on the wall.
     
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