Tile Floor Sandwich
I need some advice and validation before I start installing my heated tiled bathroom floor.
We’ve completed demo, and I can now see what under the original flooring, it ¾” tongue and groove strand board. Upon inspection, the builder was somewhat light on attaching it to the floor joist, so my first step is to finish securing with a few more nails.
Now for a few questions ….
Is ¾” T&G adequate for support, I know any give in a tile floor is a bad thing. I’m not seeing any give, but I don’t mind going to entra effort/cost just to make extra sure. I plan on covering the subfloor with a ½” cement board, however I’ve read various information that some suggest adding an additional ½” plywood underlayment, before the cement board, to help reinforce. Or is both a ½” plywood and a ½” cement board together overkill?
I plan on using Suntouch WarmWire product, and Ditra underlayment for my floor.
Therefore if I go with this logic, my tile floor sandwich will be the following:
Unmodified thin set
Suntouch Warmwire Product and ¼”self-leveling mortar
½” Cement Board
½ Plywood reinforcement
¾ T & G Subfloor
Any thoughts or feedback on this layout would be appreciated.
Check the Schluter website www.schluter.com. There is extensive information on exactly how to install tile floor, including tile floor with electric heat, using their Ditra product. They discuss at length minimum required subfloor requirements.
Thanks for the input.
I have read, and re-read based on your suggestion, now I'm wondering if I can use the Ditra product. I'm using a mosaic basket weave tile, based on the data for heated floors, the minimum tile for use is 2" x 2". Therefore I think this excludes the use of Ditra.
I have a mosaic style stone floor in my kitchen. The stone is from Bali, and includes quartzite and several other types of stone. The stone comes in 12"x12" mesh backed pieces, and each piece includes anywhere from 5 to 20 individual pieces of stone, glued to the mesh, and arranged relatively tightly.
We installed this mosaic stone in the kitchen over electric heat, and used Ditra between the thinset that covered the electric heat and the tile thinset. This was several years ago, it has worked very nicely. I am not sure why Schluter believes that the minimum tile size is 2x2 inch, you can always give them a call. In my case, some of the stone pieces are smaller than that, and it has not been a problem.
I don't think it would be a problem but Schluter says that cuz of the 1/2" divots in Ditra. They're afraid a small piece like 3/4" tile, would not be properly supported under load. Remember the spec covers commercial installations too.
Here's what you can do. Remember I will not guarantee it and neither will Schluter. Fill all the divots after installing the Ditra then install the tiles the next day. I believe this will solve any problem.
Your sandwich in post #1 is just fine, but you do not need the 1/2" concrete backer unless you need it for height. If you do need it for height, you're better of going 5/8" ply and using the CBU made for floors which is 1/4" or so depending on brand. Plus, don't forget the SLC over the SunTouch may end up being thicker than planned. It'll seek it's own level.
I'm assuming the subfloor is OSB and so the house isn't real old, and therefore the joists meet L360 deflection....right?
Thanks for the reply and input.
The house was built in 1995, and the subfloor is OSB. Although I havent validated the L360 deflection specification, I assume it does meet based on the age of the house.
I have an email into Schluter regarding the use of Ditra, and the use of smaller than 2" x 2" tiles. Hopefully I'll get an answer to help validate my applicaton.
Now I'm ready to begin the re-building process, if I can get my wife from changeing the design layout hour by hour.
I received a prompt reply from Schluter Systems.
Good morning and thank you for contacting Schluter-Systems! Unfortunately the mesh does not make a difference with your tile being under 2" X 2" as far as the warranty. Therefore if you did proceed we would not be able to provide a warranty for your application. However people have proceeded, voiding their warranty, but have success. Our best recommendation outside of the DITRA guidelines would be to prefill the cavities on top of the DITRA with unmodified thin set, after installing it to your substrate. Then proceed after 24 hours with the rest of the thin set and installing your tile.
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