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Old 02-09-2011, 08:13 PM   #1
Stu27
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Stu's master bathroom remodel

Hello,

First post on the forum. Have enjoyed occasional visiting and reading for several years now.

I am in the middle of a master bathroom remodel. Have completed the demo, plumbing changes, and most electrical. Starting to detail plan the floor. I am looking for guidance about floor height and types of thin-set. I am not a pro, but enjoy doing home projects (some tile experience… two full-bathroom ceramic tile replacements jobs, floor and bath/shower, but never used radiant heat or isolation and final floor height was not an issue)

My plan is to install tile and radiant heat on the bathroom, vanity room, and closet floors as follows:

Layers:
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9. tile (porcelain, 3/8" thick, 18" square, over three rooms, about 117 sq. ft.)
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8. thin-set (3/16"? for larger format tiles)
----------
7. isolation membrane (ditra 1/8")
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6. thin-set (1/16"?)
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5. radiant heat mat (1/8") (nu-heat custom one-piece mat over three rooms, about 68 sq. ft.)
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4. thin-set (1/16"?)
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3. new underlayment (3/8in ply)
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2. existing subfloor (19/32in T&G ply)
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1. existing joist (2x10, 12ft unsupported length, 16"o.c.)
----------

I'm concerned about the tiled floor height and the transition from the bathroom to the carpeted master bedroom. The thin-set thickness above are my estimates based on my readings here.
3/8 underlayment + 1/16 mortar + 1/8 mat + 1/16 mortar + 1/8 ditra + 3/16 mortar + 3/8 tile = 1-5/16" total height -- assuming I got the thickness estimates close… yikes! that's pretty high. Am I headed down a path that will lead to a large height difference from tile to carpet or is this manageable?

One thought I had was to ditch the plywood underpayment altogether and do a subfloor / heat mat / ditra-xl / tile approach. Schluter claims the ditra-xl is good over 19/32 T&G with 16"o.c. joists. That would save about 1/4 inch in height. Is this a better approach… a good compromise to floor strength, tile isolation, and floor height?

And here's what I think I know about the mortar:
- layer 4 under the heat mat = acrylic or latex modified thin-set (as spec'd by nu-heat)
- layer 6 under the ditra = latex portland cement (as spec'd by Schluter)
- layer 8 under the tiles = unmodified thin-set (as spec'd by Schluter)
Is there a particular brand that is recommended for any of these, or is what I can get at HD okay (figured I could use Versabond for the modified thin-set layer 4)? I'm happy to get specific types at the local tile place if that's the better route.

Thanks,
Stu
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Old 02-09-2011, 08:26 PM   #2
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Myself, I would leave the extra plywood and ramp under my carpet if I needed to. The thinset under your tiles won't build up 3/16, more like 1/16 to 1/8.
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Old 02-09-2011, 08:55 PM   #3
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They make shims placed under your carpeting to handle this very problem.

They had the crazy idea to call the website .... wait ... here it comes....

www.CarpetShims.com



I should get commissions or banana bread at least
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Old 02-10-2011, 04:10 PM   #4
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Thanks... the carpet shims are a great solution! Will stick with the underlayment.

Banana bread?... I thought beer was the standard for bartering on this forum
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Old 02-10-2011, 05:07 PM   #5
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Send banana bread and beer. We'll figure out how to divide it up.
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Old 03-21-2011, 05:01 PM   #6
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Floor Thickness and Flatness

I fInally finished up the electrical and drywall… now back to the floor.

What's the minimum thickness underlayment I can put on top of the 5/8" sturdi-i-floor to give the 18" tile the floor stiffness it needs? The complete floor description is in the first post. I was thinking 3/8" underlayment but my basis wasn't a quantifiable stiffness improvement, but rather achieving an "acceptable" carpet to tile transition.

The existing 5/8" sturd-i-floor subfloor is fairly level overall (17 ft x 9 ft) but not very flat. It has three valleys. Each valley is about 1/4" deep at its low point and each valley crosses a couple of joists (in the 17 ft dimension). Each valley runs most of the distance parallel to the joists (in the 9 ft dimension). The area below is the finished family room. Hope that was clear… not sure I can post pics yet.

I plan to install the underlayment and correct the flatness before proceeding with the heat mat, followed by ditra and tile. After I put the underlayment down on the subfloor, are these valleys considered shallow enough that thinset could be used as a leveler only in the valleys and allowed to dry prior to the heat mat installation? My takeaway (from reading only) on SLC's is that they perform best for deeper pours and would be less effective for shallow pours like this. Looking for some guidance on the proper approach / product type to improve the flatness.

Thanks,
Stu
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Old 03-22-2011, 04:38 AM   #7
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It sounds like your floor joists are causing the valleys. It would be best to pull up the subfloor and sister those low or sagging joists to get rid of the valleys.

If you don't want to re-work the joists, look for a floor leveling compound that allows you to go feather thin over plywood. It probably won't be a SLC, though. Ardex's Feather Finish looks like a good choice. A good modified thinset may work, but it is not really intended to be a leveling/flattening product.

3/8" is the minimum acceptable plywood for adding to your subfloor. 1/2" would be much better in terms of decent plywood and floor stiffness. Do any flattening with patching compound on top of this second sheet.
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Old 03-22-2011, 08:13 PM   #8
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Thanks Bob. Decided the extra 1/8 inch in height was more than manageable and went with your recommendation to go with the 1/2 inch underlayment. Picked up half a dozen sheets tonight.

It would be quite an effort for me to sister the joists in order to start with a level and flat foundation, the area to be tiled spans three rooms and has four walls (two corners) over the floor.

The Ardex Feather Finish seems like just what I'm looking for to address the local valleys. Mapei Planipatch looks very similar. Trying to find one or the other (haven't seen them at the big box stores), but will check the local tile supply folks next.

Again, thanks for the guidance.
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Old 03-24-2011, 04:45 PM   #9
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Shower Tray Subfloor

Should I extend the 1/2" underlayment (which is on top of 5/8" sturd-i-floor subfloor) to beneath the Kerdi shower tray? Wouldn't doing so stiffen the floor beneath the shower, which is desired?
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Old 03-26-2011, 06:31 AM   #10
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bump.
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Old 03-26-2011, 07:20 AM   #11
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You sure can. The additional plywood would make the floor stiffer between the joists.
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Old 10-28-2011, 12:46 PM   #12
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thinset type for river rock shower floor

I'm finally nearing the finish line on this job. What remains is to set the tile on the kerdi shower floor. I've used ditra-set mortar everywhere, either modified with 425 admix or unmodified, as required.

For the shower floor my wife has chosen river rock. I'm not sure which thinset type to use on the river rock, modified or unmodified. I did a quick test with unmodified and the rocks don't seem to adhere well to the thin set (I could pop them off pretty easily after 36 hours). I did remove the rocks from the mesh backing so they were set individually in the test and I plan do the same for the shower floor (the rocks had a ton of hot glue on them to hold them to the mesh backing and I figured this wouldn't be good to leave this layer between the mortar and the rocks).

Would the fact that they popped of so easily in the test be primarily due to the fact that the rocks are much smoother and less porous than the bottom of a typical tile (not roughed up so to speak)? Is this a case where modified thinset should be used for better adhesion to the rocks? If the recommendation is to use modified, should I allow for a longer dry time (especially because it's the shower floor)?
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Old 10-28-2011, 01:32 PM   #13
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I wonder if the hot glue didn't somehow seal the backs of the rocks, making it difficult for the thinset to bond well. Were you able to see if the rocks absorbed water after removing the glue?
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Old 10-28-2011, 01:52 PM   #14
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A quick check with half a dozen of the rocks. Water doesn't appear to absorb on either side of the rock, the bottom (hot glued side) or the top. It just beads.
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