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  1. #1
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    Jul 2012
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    Default Questions about thin-set for bathroom project

    Hi guys, this is my first major home renovation project so I could really use some help.

    So here goes: I gutted my bathroom and installed hardiebacker cement board. Now, I know that thin-set should be used to seal the seams between CBU, so I went out to the nearby Lowes to pick some up. Unfortunately, none of the things I saw on Lowes site were actually sold in the store, so I ended up picking up something totally different. What I got is Totalflex Universal Mortar, by TEC Skill Set. The stuff is latex modified and exceeds ANSI A118.4 and A118.11, so I was planning on using it for the tile as well. However, after doing the seams with it yesterday, I'm having doubts. Is the product I bought a thin-set, or is it a mortar? Is there a difference between the two? And I also read something about latex modified thin-set requiring a very long period to fully dry and cure. Am I still on the right track or did I mess up by getting the Totalflex? Thanks everyone.

  2. #2
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    Default Re: Questions about thin-set for bathroom project

    For thinset, I've used MAPEI THIN SET (from Lowes) many times, with good success. It dries relatively fast (in my area in 24 hours) and ready for grout in no time.

    For the gap between cement boards, I use tape, then thinset on top. This will allow the boards to give a little in a case of a quake (we are on a fault).

    Basically thinset is a type of mortar. In thinset they use finer sand and it's used when less of that stuff is needed (up to 1/4" deep). Mortar has rougher sand and is used for deeper beds. For bathroom floors and walls tiles you want to use thinset. For floors use porcelain tiles and for walls you can use ceramic.

  3. #3
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    Default Re: Questions about thin-set for bathroom project

    The Mapei thin-set is actually exactly what I had my eye on. But even though they had it on the Lowes site, the store itself did not have it available. All that were there were various TEC Skill Set products.

    For the Totalflex that I ended up getting, it says it can be used in both thin-set and medium-bed applications, and works with all tile sizes. So I guess all I wanted is just reassurance that what they say is actually true... Especially since I'm not certain how it can be, since like you said dj1, one uses finer sand while the other has coarse.

  4. #4
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    Default Re: Questions about thin-set for bathroom project

    Tec makes some pretty nice stuff.

    If you installed the CBU on the floor, you were supposed to set it in a bed of thinset before nailing / screwing each sheet down. For the walls, the sheets are to have a 1/8" gap with no + shaped intersections only T shaped ones.

    What kind of tiles are you setting on the walls?

    Most importantly, what is your waterproofing in the wet areas?

  5. #5
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    Jul 2012
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    Default Re: Questions about thin-set for bathroom project

    Ceramic tile on the walls, porcelain on the floor. I was planning on not putting CBU on the floor, as I've completely removed the original tile and mortar (it was crumbling garbage anyway), and now have the concrete foundation to work with. My plan is to use leveler to even it out, and then apply tile directly to that. Unless there is some reason why cement board is integral for the floor's integrity?

    As for waterproofing the walls, I used plastic sheeting under the CBU in the bath/shower area, and I've been debating whether or not I need to use something like Redgard to cover the CBU. I have the hardiebacker kind, and aren't they made with portland cement, which is supposed to be practically waterproof? Do you think I should invest in the Redgard (or some other such product) anyway? As for intersections, I have a few + shaped ones actually. Is that a significant problem?

  6. #6
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    Default Re: Questions about thin-set for bathroom project

    If you are working over SOG slab on grade then there is no need for ceement boards on the floor.

    If you have sheet plastic on the studs under the ceement board, then you don't want to add the red guard. You want one or the other. The sheet plastic needs to overlap the tub flange. The cement board does not over lap the tub flange.

    No ceement board is water proof. They are water resistant, but then so is my shirt, which isn't damaged by water either. Ceement baords suck up water like a sponge, and wick it to the studs so you can see the need for either a surface water proofing or the sheet plastic.

    While 4 mil is the minimum, 6 mil is better.

  7. #7
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    Default Re: Questions about thin-set for bathroom project

    A SOG does seem to be what I'm working with. I googled the term and found a diagram that matches up well with what I can see of the foundation. And thanks so much for clarifying about the sheeting and waterproofing. It's good to know I don't have to worry about the latter, at least.

    But about flooring, I was talking to a friend recently, who suggested that I make a subfloor of some kind instead of applying setting tile directly on the SOG, to prevent the tile and grout from cracking as the house settles or otherwise shifts. How important would you say this is? The house is about 50 years old, so settling shouldn't be an issue from what I understand, but the foundation had a few minor cracks in it that I have patched. However, I'm worried they might reappear in some years and damage the tile. So should I put in some extra work now to avoid that headache further down the road? And if so, how should I go about it? My friend suggested either plywood and CBU, or a Schluter-DITRA membrane. Would it be worth doing either of these? Thanks for all the help!

  8. #8
    Join Date
    Jan 2010
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    Default Re: Questions about thin-set for bathroom project

    Quote Originally Posted by Trueflame View Post
    A SOG does seem to be what I'm working with. I googled the term and found a diagram that matches up well with what I can see of the foundation. And thanks so much for clarifying about the sheeting and waterproofing. It's good to know I don't have to worry about the latter, at least.

    But about flooring, I was talking to a friend recently, who suggested that I make a subfloor of some kind instead of applying setting tile directly on the SOG, to prevent the tile and grout from cracking as the house settles or otherwise shifts. How important would you say this is? The house is about 50 years old, so settling shouldn't be an issue from what I understand, but the foundation had a few minor cracks in it that I have patched. However, I'm worried they might reappear in some years and damage the tile. So should I put in some extra work now to avoid that headache further down the road? And if so, how should I go about it? My friend suggested either plywood and CBU, or a Schluter-DITRA membrane. Would it be worth doing either of these? Thanks for all the help!
    Ditra is a "decoupling membrane" which isolates the tile from slab movement. Which is the only thing you need. Backer board on the floor is a waste of material and adds 1/2" of height.
    Casey
    Remove not the ancient landmark, which your fathers have set.

  9. #9
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    Default Re: Questions about thin-set for bathroom project

    Backer boards provide no structural support nor any crack supression. Plus most CBU manufacturers require mechanical fastening (nails or screws) which would be quite a challenge over a slab.

    There are crack supression membranes such as Nobleseal CS, CBP crackbuster Pro, and Greenskin. Ditra makes no claim to supress cracking as it is an 'uncoupling membrane'

    OBe sure to include expansion joints as needed to help eliminate tenting and cracked tiles. Read pages 20-23 of the 2011 Ditra installation handbook to learn all about the required perimeter and field expansion joints.

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