Resin Backed Marble Mosaic Tile - Bathroom Remodel

[dwestfa]

Hello,

My wife and I are weekend warriors tackling our bathroom renovation. We've searched the forums for advice and found it to be quite helpful. We have a few remaining questions though that we were hoping someone could help with:

1. In the tub surround, we are hanging 12x24" Carrara in a brick pattern.
--We've replaced the greenboard with 5/8 cement board, taped and mudded using white modified thinset (Custom Building Products Premium Marble and Granite Fortified Premium Mortar from HD).
--We are will be rolling on the HD version of Red Guard.
--We plan to seal with Miracle Sealants 511 impregnator before and after grouting.
--We are using a gray unsanded grout.
Our questions are: What trowel size should we use to set the tile (we plan on back butering too)? Is the white thinset we chose sufficient for the 12x24 tile on the walls? Should we use one of the leveling systems (HD has a cheap one similar to Tuscan) on the walls to avoid the lip? Do we need to use antislip?

2. On the floor, we are setting 12x12" Carrara and Grey Marble mosaic tile (~1/4 pieces), which has a thick resin backing that covers the entire tile.
--We've pulled up the old tile and most of the old mortar so no more than 1/8" is left on the two layers of 1/2" plywood underlayment.
--We are going to lay Ditra and Kerdi Band using the same thinset as the walls.
Our questions are: What should we use to set the resin backed marble mosaic tile since the bag of thinset says not for use with resin backed tile? Will the thinset work or do we need to use an epoxy like Latapoxy 300? What trowel size should we use to set the tile?

I tried a small test piece of the tile using our thinset and after 12 hours gave it a knock and it came right up - did I not leave it alone long enough? We also tried pouring water in the back of the tile to see if the resin happened to be water based. The water rolled right off and didn't seem to have any effect on the resin.

3. Based on everything we've told you, are there any glaring errors or mistakes waiting to happen?

Many thanks in advance. Sorry for the long post.
--Nick and Dana

[Davestone]

1.Hopefully the gray isn't dark.Be advised carrera can take a long time to dry after it is set from the thinset being over waterproofing.I would use a 3/8 notch.I never use the levellor systems myself but it may help you.

2. I'm not familiar with that thinset but i think it is too thick for under your Ditra and not modified..I would use a regular polymer modified like Versabond.Now the problem wth the resin backed, you need to also use a modified to stick to it,but Ditra wants you to use an unmodified.1/4 or 3/8 trowel.

[cx]

Welcome, Nick.

I think you'll find the Marble Institute of America (MIA) requires all those resin-backed stones to be set with an epoxy adhesive. The Laticrete 300 would be a good choice.

You have a problem with the Ditra. Well, one of your problems.

Your subflooring is not adequate for a natural stone tiles, even if both layers were correctly, and differently, installed. Did you also evaluate your floor's joist structure to determine its suitability for a stone tile installation?

Back to the Ditra. You must attach the Ditra to the plywood with a modified thinset mortar meeting ANSI A118.11 standards. That's after you've scraped/ground off all the old mortar.

Then, as Stoner points out, Schluter requires an un-modified mortar be used to set the tiles on top of the Ditra. What they recommend when an epoxy mortar must be used, I honestly don't know. My guess is that they'd want you should fill all the waffles with a thinset mortar, modified or un-modified, let it cure and then set your tiles with the epoxy required for the tile backing.

But I'd strongly recommend you contact their tech service people and pose the question on your own behalf: 800-472-4588.

Now that I re-read your post and see that you intend to set mosaic tiles on this floor. If they are not at least 2"x2" in size, you cannot set them over the Ditra. Can't see what you might have there.

My opinion; worth price charged.

[dwestfa]

CX - Thank you for pointing out the issue with the DITRA and our mosiac tile, that could have been a disaster! I think we'll need to try something else. Could we use Red Guard directly on the plywood floor instead of the DITRA after we get the rest of the old thinset up? Do we even need waterproofing (there wasn't anything there before - just ceramic tile on plywood)?

You mentioned that the subfloor was not adequate for stone tiles. Can you let us know what is inadquate? The floor space in the bathroom is tiny 4'10" by 7', so I didn't give the structural issues much thought.

Thanks!!!