combining different uncoupling membranes due to mosaic inlay

[tompoh]

Hello everyone,
I have an interesting challenge tiling a foyer with 12"x12" square field tile with a 36" round mosaic inlay in the center. Some of the mosaic tile are as small as 1/2"x3/4". The substrate is concrete, and in good shape; flat with no cracks at least for now. The field tile is .3" thick, and the inlay is .4" thick.

The challenge is to determine what uncoupling membrane(s) to use under the mosaic inlay, and how to make up the .1" difference in height between field and inlay. I've always used normal Ditra when installing non-mosaic floor tile.

My schluter rep suggested to use DitraXL in the field, and normal Ditra (for .1" height adjustment) with Kerdi in the inlay area. His reasoning for adding the Kerdi is to increase support under the mosaic tiles. I'm not convinced adding the Kerdi will add significant support under the mosaic. Any thoughts?

Another potential solution is to use normal Ditra under the field tile, and NobleSeal CIS under the mosaic. This should better support the mosaic inlay tile, and raise the field tile .1" relative to the mosaic inlay. Does this sound like an okay solution? I'd appreciate any input, especially criticism. I'm concerned that combining different membranes will defeat the uncoupling or cause other problems.

Tom

[CaliGrown]

I like option 2, if you’re set on using an uncoupling membrane. Have you done a mock up to figure your installed assembly with the field tile? Also how fksy have you gotten your slab?

[tompoh]

yes, I mocked up the .3" height field tile on ditra with thinset under/over. The resulting field tile height is .6".

NobleSeal CIS/TS is .03" thick, the inlay mosaic is .4". I'm hoping the thinset under/over the CIS will get me to a total mosaic install height of .6". I can't mock up the mosaic as it is one-of-a-kind.
Tom

[redlude97]

You could use schluter membrane over the ditra and under the tile to build it up. This is what schluter does over ditra heat in a shower