Does anyone have any thoughts or experience with Ditra as a tile underlayment as opposed to Hardie?
I've used Ditra under ceramic and marble tiles above and below grade with no problems. It's light and easy to work with. I definitely prefer it to doubling the ply subfloor.
Ditra is a moisture barrier and isolation membrane.
If the floor is not stiff enough tiles and grout joints will still crack.
So to clarify, over a single layer of subfloor ply on 16"OC joists, Hardi or another cement-board, glued and screwed (glued with thinset) will be rigid enough? But if using Ditra, first another layer of ply would be required/advised? Seems to make sense - do I have it right?
By the way, what kind of thinset do you use to glue down onto ply (modified or un?)
"So to clarify, over a single layer of subfloor ply on 16"OC joists, Hardi or another cement-board, glued and screwed (glued with thinset) will be rigid enough? But if using Ditra, first another layer of ply would be required/advised? Seems to make sense - do I have it right?"
That's almost the exact opposite of the way it should be.
Cement board acts as a transition material from wood to tile but offers nothing in terms of increasing floor strength or absorbing flexural stresses that floor movement can pass along to the thinset, grout and tile.
Ditra acts as a transition material, but the waffle structure of it allows it to act as an isolation membrane which means the Ditra can absorb flexural stresses caused by floor movement and not pass those stresses on to the tile.
Ditra specs are pretty much divided into two categories, so it depends on what you are putting down, ceramic tile or natural stone. Stone needs more "protection" than tile.
For tile, with joists 16" on center, the minimum subfloor thickness for Ditra is 5/8", but 3/4" is obviously better. Adhere the Ditra to the subfloor with modified thinset. Adhere the tile to the Ditra with unmodified thinset.
For natural stone, you need more floor thickness under the Ditra. The minimum is 1-1/8" subfloor thickness, usually made up of 3/4" subfloor topped with 3/8" underlayment. The Ditra goes over the underlayment.
On to cement board. Remember, cement board offers zero structural strength. It thickens the floor, but does not strengthen it.
When putting ceramic/porcelain tile over cement board, the minimum recommended thickness under the cement board is 1-1/8". Again, usually made up of 3/4" subfloor topped with 3/8" plywood underlayment. If using a natural stone, the recommendation is 1-1/4" thickness, usually 3/4" ply topped with 1/2" ply underlayment.
You then bed the cement board on top of the underlayment. First spread unmodified thinset over the underlayment, set your cement board, and fasten it down with screws or nails. Then tile over the cement board using a modified thinset.
Cement board ALWAYS needs thinset between it and the ply that it is covering. The thinset fully supports the cement board so you get no vertical flex movement due to micro-gaps between the cement board and the subfloor. That movement can cause tile/grout failure. The cement board also needs to be nailed/screwed to the subfloor. Think of the thinset as supporting the cement board and the fasteners as holding it in place.
The primary advantage of Ditra is that it allows you to minimize floor thickness build-up. Plus it can act was a waterproofing membrane if need be. Ditra itself is waterproof, but the seams between sheets are not. If you want to waterproof the floor platform (laundry room, wet room, etc), then use strips of Kerdi or Kerdi-Band over the Ditra seams.
Very helpful, thank you.
All that reminds me of my renewed appreciation for sheet vinyl, which I happened to put on our basement bathroom floor so it would feel warm to bare feet (wood ply underneath). I got a "tile" pattern and everyone that sees it says "wow, I like the tile!"
mongoct makes a good point about the different requirements for stone vs. ceramics.
But if you've doubled the subfloor for stone already, why bother with Ditra except for waterproofing?
I've used Ditra on top of the basement slab, which is prone to flexing and cracking.
The hardest time I've had is insisting that the tilesetters follow the instructions; they always want to use modified thinset where it's not supposed to be used.
See Installation Handbook below for details.
Here is a link that might be useful: Ditra Installation Handbook
Does anyone know where you can buy Ditra online? I tried purchasing it from Shag Tools but they can't ship to California.
"mongoct makes a good point about the different requirements for stone vs. ceramics."
Larger tiles have many of the same requirements as natural stone.
It is the flex over the size of the tile or stone that causes the issue.
Mosaic tiles under and inch can survive more substrate movement then 6 inch tiles.
12 inch tiles will require nearly the same treatment as 12 inch cut stone.
When you get up to even larger tiles (and stones) the surface needs to be even stiffer to prevent failures.
If the tile or stone is strong enough so that it does not crack, all the movement then occurs at the grout line, and they fail.
You might try the websites dealer locator:
Here is a link that might be useful: dealer locator
I bought mine here http://www.tileyourworld.com/catalog/
Here is a link that might be useful: tile your world
Two places I order from:
Tile-experts.com and tileprotection.com
Realize that a while ago Schluter tightened up their distribution chain, so as you discovered, some folks won't ship to certain areas.
The one advantage of Ditra that no one has yet mentioned is that it's much easier/faster/cleaner to install than cement board.
I've bought my Ditra online from Indiana Floors. Quick shipping, good service.
Here is a link that might be useful: Indiana Floors
I know there are various Schulter Ditra and Kerdi products for a competitive price on Amazon.com
My local Home Depot (Tacoma, WA) has Ditra in stock. I don't know if they carry it everywhere, but maybe worth checking.
I have 1/2" OSB over 3/4" diagonal planks. The Ditra Installation guide lists this as one of the types of floors. But, should I be hearing anything (not creaks, just a subtle popping) when I walk on the subfloor? I'm worried that I may need to lay another layer of 21/32 plywood on top, but the installation guide doesn't show installation on 3 layers of sustrate/subfloor.
If this is an older home--or even a newer home--perhaps the planking wasn't screwed down tight to the joists before the OSB was added. And the OSB may not be tight either. I have been in year-old homes that creaked and groaned like crazy for just that reason. You could go down in the basement and look up to see a series of nails that just missed the joists. When I build or renovate, the subfloor is glued, nailed and screwed.
your subfloor has to be solid before you think about adding a ditra like topping.
Apologies if this is thread highjacking, but this discussion struck me as the most appropriate for this inquiry.
When we were taking bids from contractors for our new construction house, one of the contractors specified a mud job for the master bathroom (both floor and shower) and kitchen/mudroom and Schluter Ditra for all other bathrooms.
In talking with a tile installer at a flooring store this past weekend, he said he couldn't think of a situation in new construction where a mud job (as contrasted to Ditra) would be appropriate. Is that right? We're not likely to be using any natural stone but we will likely be using large format porcelain (or possibly ceramic) tiles in some of the bathrooms (12x12, 8x24, etc.) We will have electric radiant heat pads in the floor of two of the bathrooms and hydronic radiant heat in the kitchen and mudroom.
We're flexible at this point and want to do whatever will make the installation safest and sturdiest for the long run even if it costs a little extra at this stage.
Thanks in advance for any advice.
There's nothing wrong with a traditional installation. Some tilers simply won't work with Ditra or Kerdi because they never have and never will. I've had them turn down whole house jobs rather than use new materials. Perhaps there is some miscommunication re your quote.
BTW, Ditra works with radiant heating. See Installation Handbook at link.