1/8" Schluterunder a 1/4" mosaic - do I put RedGard over the Kerdi?

[Tim Coffey]

Just installed the DensShield in the tub/shower surround. Next is to get prep for the stone mosaic I bought for one wall. Since the mosaic is only 1/4" think, I obtained a small amount of 1/8" Schluter Ditra to bump it out to match the 3/8" marble tiles.
Question is - Do I mortar the Schluter to the DensShield, then apply RedGard over everything? Or do I RedGard the DensShield first, then mortar the Schluter over that?
Or does it not even matter?

Thanks

 

[Jadnashua]

You might get by on a wall, but there's a 2" minimum size specified for tile when used over Ditra.

There are two ways to handle a shower wall...you either use a moisture barrier behind it, or waterproof the front entirely from the waterproof pan up at least to the height of the showerhead.

What are your overall plans on the use of RedGard? If you're planning on using that to waterproof the walls, then you'd not use a moisture barrier behind, and to ensure the edges of the Ditra were not open for moisture to get behind it because of the waffles and the fleece, you'd need to use Kerdiband on the edges. RedGard would not seal those edges and prevent moisture from getting behind it.

FWIW, once you thinset the Ditra in place, if your tile really are 1/4" and 3/8", the mosaic will likely sit higher than the field tile. What some do is get an 1/8" trowel, trowel thinset in that area where the mosaic will be installed...let it cure, then add thinset on top of it to set the tile. IF the area where the mosaic is going isn't too wide, you can tile above and below, then using those tile and a grout float, or something big enough to bridge those two surfaces, set the mosaic deep enough so the top surfaces are flush. The first coat and screed with the trowel will act as your height gauge. NOte, if you don't hold the trowel perpendicular to the wall, the peaks will be less than the 1/8".

Check out www.johnbridge.com for help with tiling.

 

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[Tim Coffey]

You might get by on a wall, but there's a 2" minimum size specified for tile when used over Ditra.

There are two ways to handle a shower wall...you either use a moisture barrier behind it, or waterproof the front entirely from the waterproof pan up at least to the height of the showerhead.

What are your overall plans on the use of RedGard? If you're planning on using that to waterproof the walls, then you'd not use a moisture barrier behind, and to ensure the edges of the Ditra were not open for moisture to get behind it because of the waffles and the fleece, you'd need to use Kerdiband on the edges. RedGard would not seal those edges and prevent moisture from getting behind it.

FWIW, once you thinset the Ditra in place, if your tile really are 1/4" and 3/8", the mosaic will likely sit higher than the field tile. What some do is get an 1/8" trowel, trowel thinset in that area where the mosaic will be installed...let it cure, then add thinset on top of it to set the tile. IF the area where the mosaic is going isn't too wide, you can tile above and below, then using those tile and a grout float, or something big enough to bridge those two surfaces, set the mosaic deep enough so the top surfaces are flush. The first coat and screed with the trowel will act as your height gauge. NOte, if you don't hold the trowel perpendicular to the wall, the peaks will be less than the 1/8".

Check out www.johnbridge.com for help with tiling.

It is a 39" wide, circular mosaic.

So I can skip the Schluter completely if I am just real careful about my thinset depth under the mosaic. I was hesitant to to try that, being afraid that the depth would be inconsistent, and causing a wavy appearance to the mosaic. But I did not know about sealing the edges of the Schluter to prevent water getting under it, and do not have a way to prevent that, so it seems that I am going to just use an extra 1/8" thinset layer first under the mosaic.

 

[Jadnashua]

For a mosaic that large, it will be hard to get it and keep it flat unless the surface is perfectly flat and the right height to start with. I would not try that two-step technique using a first layer of thinset and notched ridges you let cure before adding more to then set the tile...it could work, but would be tougher since you'd not be easily be able to bridge the opening onto tile that was already set.

I was thinking about it being a mosaic accent stripe, not a significant feature area that large.

One of the benefits of the Ditra membrane is the open grid underneath. When used on say a green concrete slab, it allows the slab to dry during the curing process (normally, you can't tile a green slab for at least 28-days, but with Ditra, you can do it as soon as it is strong enough to support working over it...often, the next day saving lots of time in some situations). While it can be made waterproof by sealing the seams with the Kerdiband strips, it is designed to work on floors, not walls.

 

[Tim Coffey]

For a mosaic that large, it will be hard to get it and keep it flat unless the surface is perfectly flat and the right height to start with. I would not try that two-step technique using a first layer of thinset and notched ridges you let cure before adding more to then set the tile...it could work, but would be tougher since you'd not be easily be able to bridge the opening onto tile that was already set.

I was thinking about it being a mosaic accent stripe, not a significant feature area that large.

One of the benefits of the Ditra membrane is the open grid underneath. When used on say a green concrete slab, it allows the slab to dry during the curing process (normally, you can't tile a green slab for at least 28-days, but with Ditra, you can do it as soon as it is strong enough to support working over it...often, the next day saving lots of time in some situations). While it can be made waterproof by sealing the seams with the Kerdiband strips, it is designed to work on floors, not walls.

One more bit of info: This is for a wall, not a floor. The manufacturer (Mozaico) tells me it can be installed on a wall if you cut it in half first (it is meshed), and install the two halves separately.
I thought that I could install the mosaic first, using a piece of 5/8" plywood (with the half-circle cut out in it) attached temporarily to the wall as a bottom support. Let it cure for 1-2 days, then attach the top half. After the entire mosaic is attached, I would attach the 12x12 marble tile, cutting the 8 (or so) tiles that surround the mosaic exactly to the edge of it + 1/16" gap for grouting.
Does this sound doable?

 

[Jadnashua]

If you use a good, non-sag thinset, you should be able to install things all at once. I don't have enough experience to guide you further. I have some ideas, but I think it will be a challenge getting things all flush as you wish. I'd post over at www.johnbridge.com where there are a lot of professional tilers. They may have some other suggestions. The extra complication is that you want the wall to be waterproof.