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kickstart 12-06-2017 05:14 PM

Early 50s bathroom renovation looking for feedback
Hi there, DIYre new to the forum and never done a bathroom renovation or tiling job before :)

Im hoping to get some feedback on my bathroom remodeling plans, especially with the floor tile installation.

Im planning on gutting and re-doing my early 1950s second floor dormer bathroom (full bath). Im planning on replacing all fixtures, wall tile and floor tile (basically gutting to the studs and redoing everything). I realize this will be a big challenge. On the more optimistic side, Ive been doing a lot of research and even got myself a copy of the 2017 TCNA Handbook.
Regarding the floor here are my constraints (challenges) Im working with for this remodel:
  • Wife already picked out a 7/8 mosaic hex tile
  • We want electric heating under tile
  • This dormer bathroom is only a little over 7 high at the highest point, sloping down to a little over 6 at the lowest, so Id rather not lose any more headroom than I need to.
  • In addition to the low ceiling height, the hallway outside the bathroom (and the rest of the house) has 5/16 face nailed hardwood flooring, and theres already approximately a 1 step/threshold to the existing bathroom tile floor so, again, Id rather not build up the new tile floor height much more than it already is.

Some positives:
  • Its a pretty small bathroom (about 5x8) including the tube area (so only about 5x5.5 floor tile area)
  • The original tile floor is actually in really good condition. Only one small crack behind the toilet and is pretty level with just a slight drop (about 1/8) towards the tub. So Im thinking my joist support is probably adequate for what Im putting down.
  • The upstairs appears to have a 3/4 plywood subfloor. (The first floor has 1x4? T&G solid boards)

Heres my current plan for the new floor:

Using TCNA RH135 for interior floors with radiant heat over wood as a guideline, as follows:
  1. Rip up the old plywood if its too water damaged and replace with 23/32 EGP, glued and screwed to the joists
  2. Apply modified thinset and then 1/4 cement backer board screwed to the plywood
  3. Tape and seal (thinset) seems in backer board, let dry
  4. Prime backer board with SLC primer
  5. Attach Suntouch TapeMat to backer board with staples to secure the mesh and hot glue to secure the heating wire.
  6. Run 1/4 foam insulation band around perimeter, and seal all gaps with latex caulk
  7. Apply SLC (LevelQuick RS, or ES?) to a thickness of 3/8 to 1/2 to just cover over the heatmat level/feather, let dry
  8. Apply mosaic tile with modified thinset

Thoughts on the above? Any glaring admissions?

A few notes:
  • I using RH135 instead of RH130 because I want the Res 2 wet rating of course Im using SCL instead of Mortar but believe SCL is technically a modified mortar itself
  • Im using 1/4 backer board to save some height, but using the 23/32 EGP (instead of 19/32 allowed per spec) because Id like a little more rigidity. Does this make sense?
  • This should get me to around the same height as the existing tile floor (I think), at about 1-1/14 above the hallway floor maintaining the same threshold step-up I currently have
  • I would prefer to use Ditra Heat, but I dont want to chance the installation with the smaller mosaic tile
  • Im using SLC because it seems to be a lot less of a hassle and a better finish than doing two coats of thinset, and not that much more of a cost for a small bathroom
  • Ive read the library thread on SLC, and I see that one suggestion was to spray the primary over the heatmat, but I called Suntouch and they suggested not to prime the heatmat.

Thanks in advance for your help, suggestions, and feedback!

rmckee84 12-06-2017 05:26 PM

Seems like you have a good grasp on things. One thing I can say is LevelQuik isnt rated for over CBU. Mapei has one just called self leveler I believe and it is good for use over primed CBU.

kickstart 12-07-2017 06:44 AM

Thanks for the tip Ryan!...

I just assumed Levelquick was good over backerboard. I'll look into the Mapei SLC.

rmckee84 12-07-2017 04:04 PM

I recently came into a project that was already prepped and needed to use slc to cover heating mat so I contacted Custom and they told me I couldn't use any of their slc products over cbu.

kickstart 12-07-2017 06:24 PM

The realization that this tiling stuff is a lot more involved than I originally thought has started to hit me :)

I chatted with Custom (online support). They said Levelquik can be used over CBU (specifically, they said Wonderboard), but.. that you need to prime and use lath (similar to the requirement for use over wood).

Per your suggestion, I found that Mapei has a SLC that specifically states you can use it on CBU, and use it to encapsulate electric heating wire - Novaplan Easy.

I also called Mapei. I forgot the guys name I talked to (sorry), but he seemed pretty knowledgeable. He said to prime with Primer T and there's no need to use lath, at least for an area as small as a bathroom. BUT... here's the kicker... when I asked which of the many SLC's they sell to use (expecting him to reply with "Novaplan Easy"), he said any of them will work fine over CBU. :shrug: Anyway, I think I'll go with Novaplan Easy. Now to find a place that sells it.

The Mapei tech support guy had some good suggestions:
He said he'd prefer to use heat wire instead of the heatmat as that would give the SLC more contact area with the CBU. He would also like to have the primer applied after the heatwire was fastened down, due to possibly contaminating the primer coat by walking on it when installing the heat wire. I think I'll double check with the mat manufacturer and see if it's OK to prime the heat wire.

So... there isn't a good consensus on the finer details here... as in what SLC's are OK to use over CBU, or which ones are the best in this application... or the best way to embed heating wire/mats.

It's funny, I ask the heating mat company about how to go about embedding the mat in SLC and they say "what do do the instructions of the self leveler you're using say, you need to follow their instructions"... and I ask Mapei support the same question, and they say "you need to follow the instructions from the heating mat manufacturer" :)

kickstart 12-08-2017 12:17 PM

Thinking about my subfloor prep some more... I'm wondering if the 1/4" of CBU is redundant if I'm using SLC.

I see TCNA has a spec - RH140 which is just 1/2" of SLC on top of 3/4" ply, with the heat wire encapsulated in the SLC. It's only a Res1 rating... but maybe I'm better off putting a membrane on top of the SLC anyway, especially considering the floor can get pretty wet next to the tub (at least in our house).

rmckee84 12-08-2017 03:10 PM

CBU adds no strength to a floor so I would say there is no real advantage to adding it.

kickstart 12-15-2017 04:49 PM

I'm going to go with TCNA RH140 then.

I've called both Ardex and Mapei to get their suggestions on this spec.

Ardex recommends their Liquid Backer Board.

Mapei said any one of their SLC's would work, but for my needs their product they sell at Lowes, or their Novaplan Easy Plus would be my best options.

I'm leaning towards using the Ardex LBB, as it doesn't require lath and I've read some posts that mentioned it flows better than most SLC's.

Also, I plan to put down NobleSeal CIS over the LBB... because I'm concerned about cracks with a LBB/SLC encapsulating heat wire, and because I'd like some extra wet protection (RH140 is only rated Res 1). The NobleSeal rep I talked to recommenced CIS over TS for this application.

Only thing I still need to confirm is if the heating wire company is OK with the NobleSeal CIS... I'm pretty sure it is (NobleSeal is approved for use over heating), but I just want to make sure.

I figure if I'm going to buy some NobleSeal CIS for the floor, I might as well get some of their product for the tub surround... thinking about their ValueSeal.

So... my question now is... Anyone know if I can purchase small quantities of this stuff. I only have 30sq-ft of floor area (CIS) and 70sq-ft of wall area (ValueSeal) to cover.


TheMaxwellInn 12-15-2017 05:46 PM

They may have told you to primer afterwards as much to ensure you don't contaminate it by walking on it as they are trying to keep you within the set time for Primer T. There is a time window to use it once applied, and if you exceed that time, you need to reapply.

I used it for thinset over gyp-crete and it worked very well and eased any concerns I had about thinset over a gypsum product.

In a 1950s bathroom, you might find that you've got 1x6" on diagonals across joists and then some plywood subfloor product above that from a later remodel. It's always a guessing game with 1930-1970 with what you'll find under the tile/linoleum flooring of the day.

kickstart 12-15-2017 10:13 PM

Yeah... it's going to be interesting to see what I'm dealing with when I start the demo. I'll post pictures as I go

kickstart 12-15-2017 10:30 PM

So I did get a hold of Suntouch support today. You can use their mats and heat wire with a membrane over it. However. they would prefer the membrane be under the heat mat/wire, as the membrane will act as a thermal insulator.

So... now I'm thinking a fabric membrane might not be the best idea... especially Nobleseal CIS, which I believe is around 0.8mm thick. (or maybe it's the R-value that's 0.8)

Using Ardex's 8+9 liquid membrane, or Mapei's AquaDefense, seems like a better idea, as I assume it has a much lower R value compared to a fabric membrane.


John Bridge 12-16-2017 10:52 AM

Hi Chris,

Lots of membrane people want their membrane on the substrate beneath the wire, but I don't think any of the tiling membranes would amount to much of a thermal break. :)

mark999 12-16-2017 02:08 PM

what kind of tile are you using? If it is natural stone you will need an add. layer of 1/2" min. plywood on top of the existing 3/4" plywood.

kickstart 12-16-2017 08:15 PM

Thanks John...

I might just go with the liquid membranes anyway, as it seems easier to apply (though maybe not?), and cheaper. I could also use the same product on the tub surround (which I guess I could do the same with the fabric, but with 3x6 subway tiles I was worried about fabric build-up in the corners being tough to tile over).

Hi Mark,

Floor tile is a 1" (7/8"-ish) hex ceramic/porcelain mosaic... so I think I'm good there. However, I was just thinking through my plans and realized that with just 3/4" ply and 1/2" of SLC that I might end up lower than the existing floor (which may be a headache with the toilet flange). I'll have to take some measurements once I have everything pulled up, but I was thinking that if I have the room I might as well add some more strength with an additional layer of plywood.

My floor tile is about 3/16" thick - do I assume 1/8" for thinset? If so, the new installed floor thickness including subfloor would be around 1-1/2 to 1-9/16", following RH140. I believe the current floor is around 2" thick including the subfloor. So another layer of 1/2" ply would be just about right.

I guess I would then be doing a hybrid of RH130 and RH140.. which I assume is fine. I actually don't quite understand RH140 as it seems weaker than the other TCNA standards (especially considering it's for 19.2" joist spacer). I guess SLC provides additional strength compared to CBU?

Houston Remodeler 12-17-2017 12:30 AM

Neither SLC nor CBU provide any structural strength

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