Hey guys, reading up on Ditra.

My current application, i'm using plywood sleepers 8" oc, heat transfer plates, and my plan was to drop hardibacker on top of this, then tile in bathroom/kitchen, floating hardwood in other rooms.

My question about ditra is, the installation instructions don't talk about the sleeper method specifically, is it acceptable to skip the hardibacker use the unmodified mortar then ditra to put the tile on?

Second Questions, if I was to use the sleeper to hardibacker method, should I put Ditra on top of the hardibacker as well, or is that overkill?

A few pics of my work in progress:

Thinset is not compatible with the transfer plates. Ditra must be put down with thinset, generally unmodified or rapid-set, while you can simply screw down the hardibacker if you are confident of the stability and flatness of the substrate (in your case, the sleepers).

Ditra is an uncoupling membrane in your application (unless it will get a lot wetter inside than I anticipate). Whether you need it depends on the relative expansion rates of your tile and substrate. If you are putting down ceramic tile (rather than natural stone), I doubt you need the Ditra.

But, I'm just a DIYer and my opinion is worth what you paid for it.

i was nervous about thinset and aluminum plates for awhile, but I've been told that once set, the thinset is pretty inert stuff, and I've never heard of any major problems with thinset over plates.

I've seen just about every tile detail possible done over sandwiches... no known issues to date. Best of luck.

To clarify a bit - When setting Ditra you use a thinset appropriate for the substrate, in the case of plywood this would be a modified thinset. If setting Ditra over a cement board then you would use unmodified thinset to install the Ditra. Installing tile over Ditra is always done with an unmodified thinset.

I don't think Ditra directly over the plates and pex is a good idea. In this case I would probably just use a cment backer board and then tile. Schluter technical support is very good, you can call them and get their take on using Ditra.

Schluter Systems L.P.
194 Pleasant Ridge Road
Plattsburgh, NY 12901-5841

Tel.: 1-800-472-4588
Fax: 1-800-477-9783

I thin setted 1/4" hardi backer to my sandwich then thinset tile. I think the ditra alone would not reflect as true of a plane over a sandwich.

For the cost of ditra I would skip it, and use the hardi backer. Unless build up height is an issue.

Gordy

Thanks for the replies!

my subfloor is 2x12 planks, with the 3/4" plywood sleepers on top so I'm pretty comfortable it is stable, and no build up height issues.

My original plan was Subfloor, Sleepers with plates, Hardibacker, thinset and tile and yeah I'm thinking natural stone for both rooms but the wife might have something more to say there...

Looks like I'll just stick with that plan!

Thanks guys.

Radiant considerations aside, when wonderboard is thinset to a substrate and then tile thinset to the wonderboard, the resulting floor is a 1" solid monolithic structure whose firmness is hard to beat. I personally can't stand flexy floors and by golly that's the way to stiffen them.

Yes, They say that hardi backer adds no structural value to the floor.

But when you thinset the hardi backer, and screw the crap out of it then tile. There is a noticable difference in the stiffness of the floor when finished.

Gordy