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-   -   Ditra:can I make up 3/16" difference between old & new floors w/ thinset under Ditra? (http://www.diychatroom.com/f5/ditra-can-i-make-up-3-16-difference-between-old-new-floors-w-thinset-under-ditra-68398/)

lazzlazz 04-05-2010 11:39 PM

Ditra:can I make up 3/16" difference between old & new floors w/ thinset under Ditra?
 
Have 3/16" difference between small area of old subfloor (lower) and new subfloor.
Home Depot guy (I know ... that's why I'm checking) says it should be ok - but use 3/8" notched where I'm trying to build up floor)..
The plan is granite tile; I've got a decent subfloor & underlayment. Tiles will span the old & new subfloor (next to tub & toilet). Floor otherwise is pretty level. I'm guessing I want to feather out modified thinset very gradually away from the place where the two floors meet? (at least 2 tile widths (12 x 2)?).

Didn't find anything in the Ditra handbook which expressly prohibits this. What do you with experience working with Ditra think?

ccarlisle 04-06-2010 08:54 AM

There are 2 thicknesses of Ditra' HD usuallly carries only the original. But no, Ditra can't be 'floated' over thick thinset, it's meant to be pressed firmly onto the subflooring with a float.

ratherbefishin' 04-06-2010 11:06 AM

Go back to HD and introduce that guy to the bags of HENRY Levelpro he's got sitting on the shelf:whistling2:

Bob Mariani 04-06-2010 02:49 PM

you can skim coat the thinset to gain some height. let it cure. Then do the nomal Ditra installation.

lazzlazz 04-07-2010 12:49 PM

Quote:

Originally Posted by Bob Mariani (Post 424834)
you can skim coat the thinset to gain some height. let it cure. Then do the nomal Ditra installation.

Thanks.
Do I use the latex-modified thin set for this skim coat then? (Schluter handbook says latex-modified thin set for placing Ditra in, then unmodified thin-set above the Ditra for setting the tile in).

If I really should be using self-leveling compound I can, but I have a 50 sq. ft. bathroom and I already have far more thin set (both modified & unmodified) than I need, so if I can get away with the thin set build-up, it would be nice. But I don't want cracking, etc. under my tiles down the road!

ccarlisle 04-07-2010 01:21 PM

The choice of modified or unmodified thinset to place Ditra has more to do with what the subfloor is made of than the Ditra itself.

On the other hand, you use unmodified to set the tiles on the Ditra - that's another story..

Bob Mariani 04-07-2010 02:22 PM

if you are concerned about cracking then use the modified which will be more flexible. But the cracking will not transmit into the tile since you are using the Ditra which isolates these cracks from the tile. (a decoupling membrane)

lazzlazz 04-07-2010 05:19 PM

Quote:

Originally Posted by ccarlisle (Post 425321)
The choice of modified or unmodified thinset to place Ditra has more to do with what the subfloor is made of than the Ditra itself.

On the other hand, you use unmodified to set the tiles on the Ditra - that's another story..

Underlayment is 1/2 inch plywood. Schluter says to use unmodified thinset for under Ditra.

I was just wondering about whether it's fine to use unmodified thinset for *building up the floor* (to make up the 3/16" difference between old & new floors). Based on Bob's answer, it seems it's ok.

Sorry for all the questions, but I'm new to this and I'd rather ask questions than do it wrong.

By the way, since the plywood has 1/8" gaps where one sheet joins another, I'm guessing it's fine if that gets filled with thinset?? The gaps are there for expansion so that's why I'm wondering - do the pros avoid the gaps, or is it not a problem for thinset to get in them.

Bob Mariani 04-07-2010 06:00 PM

use caulking to fill these or tape them (best way)

Bud Cline 04-07-2010 07:31 PM

Quote:

Schluter says to use unmodified thinset for under Ditra.
NO IT DOESN'T - Read it again.

ALSO, did you know that granite tile is thicker than most ceramic tile? Granite tile will be 3/8" thick. Personally I don't think you will have as much variance as you say you will.:)

Use a cheap caulk to fill the plywood gaps.

tpolk 04-07-2010 07:36 PM

hope you meant your underlayment is 1/2" not the subfloor

ccarlisle 04-08-2010 07:31 AM

No, no; in your case, if you are laying the Ditra on top of plywood, then you use modified thinset to do so BUT you use regular, unmodifed to lay the tiles onto the Ditra.

I thought we were clear on this, but obviously not. Look don't mess around with thinsets - they are suggested for very good reasons and your job is to take the advice given - and apply.

jobondur 04-09-2010 02:30 PM

Quote:

Originally Posted by tpolk (Post 425485)
hope you meant your underlayment is 1/2" not the subfloor

Tpolk raises a very good point. Is 1/2" plywood all you have on top of the floor joists? I don't think that's enough to support marble without flexing a lot and cracking up your grout joints but you should probably have 3/4" plywood as an absolute minimum.

I'm definitely not a pro though, so maybe someone with more knowledge could chime in on this...

Also, after reading tons of forums on this, the choice of modified or unmodified thinset depends on the two layers of material you are putting it between. Unmodified thinset will cure completely in a couple of days between two layers of material that barely breathe (i.e. concrete, ditra, and tile). Modified thinset will take a month or so to completely cure in between two layers of material that barely breathe. So if you're using modified thinset you should be applying it over something like plywood that will allow the required evaporation to occur. Unless, of course, you are ok with staying off the tile for a month.

And don't use cheap unmodified thinset, it should cost somewhere between $10-$20 per 50 lb. bag. HD sells CRAP for $5, don't get that (just paraphrasing what I've been told).

lazzlazz 04-09-2010 05:51 PM

Thanks for all the replies.
I misspoke in my most recent message, prior to this one (I said it right in my first message): Under Ditra, use Latex p.c. thinset (or modified); on top of Ditra & under tiles, use unmodified. I'm clear on that aspect, Ccarlise; p. 25 of the Ditra Handbook really lays that out nicely.

As for questions about floor under tile: underlayment is 1/2 plywood, per Ditra's specification (those specifications are "underlayment – minimum 11/32", 3/8" nom.(10 mm)-thick Exposure 1, plugged-face plywood or OSB with 1/8" (3 mm) gap between sheets")

The SUBFLOOR (under the underlayment) is 3/4" plywood.

Thanks for the concern - I don't understand all the ins & outs (that you learn with years of experience) but I am paying close attention to the Ditra Handbook. Where it spells things out clearly, I am fine.

But, I appreciate the feedback regarding taping joints. But, what do I tape them with?
Can I use the same tape on plywood underlayment that is used on Cement Backer Board? (Home Depot thinks I can ...)
http://www.homedepot.com/webapp/wcs/...f&ddkey=Search

What's better - tape or caulk for the joints? Or is it not a big deal?

I bought the Mapei Ultraflex 2 Tile Morter with Polymer (latex portland cement mortar), which meets ANSI A118.11 specifications, per Ditra specifications (over $20 per bag).

tpolk 04-09-2010 05:56 PM

duct tape works for everything...kidding


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