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Unread 02-27-2012, 02:19 PM   #1
fredhead
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Is it okay to mix durock and hardiebacker together on adjacent walls?

Is it okay to mix durock and hardiebacker together on adjacent walls?
And what type of space should be left in the inside corners where the cement boards meet?

Heres my story...

I started a remodel with the intention to use hardibacker on the 3 sides of the bathtub and ceiling. I placed 6mil plastic around the framed in tub area walls and hung 1/2 hardiebacker on the back wall and the ceiling above the tub. I stopped at the left and right walls of the tub area. I noticed that the hardibacker was not as thick as the sheetrock it would join with. Hardi is only .42 inches, not a true 1/2 inch. I see comments on this forum that the seam could be feathered but since this is my first tile job i am already facing a learning curve to tile let alone have obstacles like this make it harder. Also the cliff made by the difference between hardie and sheetrock is about an 1/8 inch (a noticable difference). I bought a sheet of durock and it matches perfectly with the 1/2 sheetrock.
I could pull everything down and either shim the left and right walls an extra 1/8 or just use durock all around. But since the hardie is up and the moisture barrier is intact, i would rather move forward then backwards.

So it comes down to... is it okay to mix durock and hardibacker together on adjacent walls? Back wall and ceiling uses hardie and the left and right walls use durock?

Also, how much space is required in the inside corners between CBUs? Both manufacturers websites have specs on board layout but neither describe corners (at least from what i could find).
Durock states: "Fit ends and edges of panels closely but not forced together."
Does this mean corners should not have a gap (like an 1/8 inch) for expansion or movement?
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Unread 02-27-2012, 02:58 PM   #2
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step 1. gap them 1/8"

step 2. mud the gap with thinset and alkali resistant mesh tape

step 3. grab a cold adult beverage


they're not gonna fight, should be just fine

p.s. the gap is not for expansion or movement; it is to allow the thinset to bond to the ends of the backerboard; creating a 'monolithic' joint. to tape without a gap would be like making a backer-board hinge
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Unread 02-29-2012, 09:43 AM   #3
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Thanks...

So the corners get a 1/8 gap. Your comment about "to tape without a gap would be like making a backer-board hinge" makes me think i should have gapped all the boards 1/8, not just the corner. The durock boards im not so concerned since they have a some what ragged edge due to the nature of the cement board cut and there is a small gap. The hardiebacker boards however cut straight and smooth and fit together with very little gap (you could slide a piece of paper between the gap). Is this going to be a problem?

Also... I am now laying out 1/4 hardibacker on the floor in the bathroom which will be tiled with 13x13 tile. The bathtub instructions (American Standards Princeton tub) shows an illustration with the underlayment and tile pushed up against the bathtub apron. It states: "The tile or similar finished floor will be butted against the bottom of the tub apron also holding the tub in place."
The hardiebacker instructions states "Keep sheet edges 1/8 inch back from walls and cabinet bases". It does not state anything about the tub but my gut feeling is to leave a 1/8 gap.

What is the correct approach?
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Unread 02-29-2012, 10:32 AM   #4
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Welcome, Fred.

Follow the various CBU manufacturers' installation instruction (no, they're not all the same) for their individual product. The treatment at the corners between brands should be clear from the corner joint requirements of either product.

I'd disregard the tub manufacturer's recommendation of using the CBU to anchor his tub in place, much as I hate to say that. You might wanna talk to them about that particular recommendation.

My opinion; worth price charged.
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Unread 02-29-2012, 10:58 AM   #5
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I looked at those installation instructions, I would gap at least 1/8-1/4 from the finished tile/substrate to the apron edge. untimely that gap would receive a flexible silicone caulk joint.

I assume you did install a fully supported stringer for the tub to rest on?

I honestly wouldn't leave it with just the apron edge and that stringer to support it, i would set it into either a bed of expanding foam or a blob of mortar for a good full support of the tub weight.

Edit: but it seems they DO NOT recommend this, they dont want any bedding material under the tub and seem to want it to 'float'; I'd call them about this and see if you can get someone knowledgeable on the phone, I certainly wouldn't want my tub just floating on air and a drain fitting.
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Unread 02-29-2012, 12:02 PM   #6
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I installed the tub about 3 months ago and i am just getting back into the project. I spoke to American Standard a couple of months ago and they stated it was okay to place the tub in a bed of mortar. It looks like the tub installation instructions for the 2390 princeton tub has been updated for 2012 to state: "Step 3: INSTALLATION - BEDDING MATERIAL (MORTAR, SANDMIX, ETC.) IS ACCEPTABLE" - Found this in the installation pdf on their website.

The tub was installed with a stringer on the back wall and the base is sitting in a bed of mortar. Both myself and my wife (350+lbs total) were in the tub recently to check the stability and it seems rock solid.

Looks like they added this also which was not on my instructions that came with the tub. O well...
"APPLY BEAD OF SILICONE CAULKING TO TOP OF LEVELING SUPPORT STRINGER BEFORE INSTALLING TUB"

I'll give American Standards a call and get their side.

Thanks for the info...
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Unread 02-29-2012, 12:43 PM   #7
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I'm going to guess the bead of caulk on the top stringer is/was to take up any unevenness in the stringer; similar to how thinset is used under backboard on floors; but that is just a guess on my part.

Glad to see they allow the use of the mortar bedding under that tub; cant believe they originally advised against it! from the photo's you'd have a water-trampoline without one!

so as said, I would gap between the floor and the apron, and if the apron is currently 'swingin in the breeze, you might use some extra framing to 'back it up' from behind, or at least a bit of polyurethane adhesive at the apron-subfloor intersect
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Unread 02-29-2012, 01:28 PM   #8
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Spoke to both American Standards and JamesHardie, both stated the floor underlayment and tile should be gaped at a minimum of 1/8 inch away from the tub.

I triple checked with AS about the Princeton tub and they said if it has the black honeycomb foam under the tub (which mine does), the tub can be set in a bed of mortar. I didn't ask about the caulk. I thought maybe it was to help prevent squeaking if the tub was not seated correctly.

I spoke to the technical rep at Hardie and USG (for the durock) and they both said in a wall layout, boards should be butted against each other.


Again, thanks for your support...
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Unread 03-27-2012, 08:16 AM   #9
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I am tiling half way up the walls in the bathroom. In the tub area, i used cement board and taped the seams with an Alkali-resistant tape and thinset.
The walls of the bathroom outside of the cement board/wet area is green board.
When taping the green board, do i use regular paper tape and joint compound or do I use the alkali-resistant tape with thinset in the areas where the tile will be set?

I found articles where tape and joint compound was used but then was coated with red guard or a wall primer. Is this necessary? Its not a wet area.

Any recommendations?

Also, before hanging the tile on the green board, do I need to coat the green board with anything to protect it from the thinset or do I just trowel the thinset directly on top of the green board and then set the tile?
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Unread 03-27-2012, 08:27 AM   #10
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1. When finishing the drywall seams in dry areas to be tiled you would use drywall finishing products. Don't finish beyond just filling and taping.

2. You don't need any waterproofing or other treatment in the dry areas.

3. You don't need to coat MR Board (greenboard, etc) with anything prior to tiling. Regular white drywall would have been the better choice for your walls.

My opinion; worth price charged.
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Unread 03-27-2012, 09:32 AM   #11
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I have a soffit above the tub area and I plan to tile the ceiling above the tub.
How do I address the outside corner where the tile (on the bottom of the soffit) meets the vertical part of the soffit that goes up to the bathroom ceiling which is sheetrock.

I found a vinyl outside corner re-enforcement used in sheet rocking, but it has a corner bead. The bullnose tile that would run along the outside edge does not lay flat due to the corner bead.
HD had a selection of outside corners but they all had a corner bead. What should be used in this situation?


Also, with your previous comment (CX), any reason to use white board instead of the greenboard in the bathroom?
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Unread 03-27-2012, 09:48 AM   #12
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You would treat that outside corner just as you would any other outside tiled corner, Fred. Bullnose, mudcap, back-bevel, etc. You don't want any sheetrock corner bead at any corner you intend to tile around.

There is no advantage whatever to using "greenboard" anywhere in residential construction that I have ever found except to satisfy the whims of the occasional code compliance inspector in years long past. None at all, now.

My opinion; worth price charged.
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Unread 03-27-2012, 11:04 AM   #13
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This is my first tile job, so I am still trying to figure out the details as i go along.

Do I need to install some type of outside corner strip first that sits under the tile that does not have a corner bead?

I won't be tiling around the corner, only the bottom of the soffit will be tiled, the front of the soffit is sheetrock and will be painted. The tile along the edge will be a bullnosed tile.

I shaved off about an inch of the bead that prevented the tile from laying flat. It wasn't easy but the tile now lays flat (except for the thickness of the strip itself). If I do need a corner strip, I can shave a 5 foot section, but it feels like a lot of work for something that should be out there.
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Unread 03-27-2012, 11:21 AM   #14
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That's not a "traffic" corner, Fred, you can just wrap it with paper tape. There is paper tape available that has very thin metal strips on each side of the center that makes very nice, crisp, straight corners with barely any build-up at all. If you intend to tile all the way to the edge (not always easy) with no reveal, that's what I'd use.

My opinion; worth price charged.
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Unread 03-27-2012, 11:25 AM   #15
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Quote:
Originally Posted by Fred
The bullnose tile that would run along the outside edge does not lay flat due to the corner bead.
Fred, If I understand correctly, your ending you tile at the outside corner? If so, you would stop short just of the bead. At least that what I prefer to do. In this picture I used a pencil instead of bullnosing. You can just make out the blue corner bead to the left.
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