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Old 12-26-2017, 09:06 AM   #1
tscoffey
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Best way to install 39 inch circular mosaic to shower wall

I am installing a tub/shower surround using 12x12 marble tiles. I am also planning to use a nice 39” circular mosaic in the center of the long wall. But as luck would have it, the field tile thickness and the mosaic tile thickness are different by 1/8”. So to make the mosaic flush with the tile, I need to bump it out by 1/8”. I had considered using 1/8” Kerdi underlayment, but was advised that I would need to seal the edges of it to keep water out – and Redgard can’t do that.

So if I can’t use the Kerdi as a bump out under the mosaic, I have come up with this method:

1- Draw a 39” circle to the DensShield
2- Redgard within the scribed circle (ie, under where the mosaic bump out board will go next)
3- Cut a 39” circular mosaic backer with ¼” Hardie board
4- Install the Hardie board circle to the DensShield using galvanized screws
5- Mortar over the screws
6- Redgard the entire surface, including the sides of the circle of Hardie board
7- Install 12x12 tile (using ¼” thinset layer), leaving a 1/16” to 1/8” gap between the tile and edge of the Hardie circle for a grout line.
8- Install the mosaic (using 1/8” thinset layer), possibly cutting it into sections first (it is on a mesh) to make that easier (it is about 40 pounds).

My concerns with this method mainly involve the Hardie board. I have seen others mention that Hardie is not really recommended in a shower area. Also, will Redgard properly seal the edges of the Hardie – or should I apply a small layer of thinset around the edge first?

My other version would be to not use Hardie board at all under the mosaic, but rather to install the field tile first (leaving a circular gap), then install the mosaic using just a 3/8" layer of thinset. But this would seem to possibly allow a lot of thinset to leak into the grout lines of the mosaic (and there are a LOT of grout lines), making grout line cleanup of thinset a very tedious process.

Ideas? Suggestion?
Thanks
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Old 12-26-2017, 12:26 PM   #2
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First off, is the mosaic design already put together?

One thing for sure, you don't want the thinset 3/8 thick. you'll have a mess on your hands. You'll want to build out with something.
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Old 12-26-2017, 12:31 PM   #3
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Yes, it is a premade (on a mesh) mosaic from Mozaico. They recommend actually cutting it into sections for easier wall installation.
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Old 12-26-2017, 01:28 PM   #4
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I would probably lay the design on a flat surface like a table top and make a template out of paper or cardboard adding a grout joint around the edge. I would then tile the wall and mark the cuts using the template.

Or, It's possible to lay out the whole wall of tiles on a hard surfaced floor leaving the grout joints and then lay the template on the tiles and mark them. I would want to set the tiles against a straight edge and get everything very accurate.

One thing's for sure, I'd want to set the thicker field tiles first, then build out the mosaic area.
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Old 12-26-2017, 01:43 PM   #5
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Welcome, Tim.

Saying that you’ve got a challenge on your hands would be an understatement. I’d do like Davy suggested where your thicker field tiles were all installed first. And I’d lean in the direction of using something like Nobleseal strictly within the circle to help build it out. Trying to use mortar to build out one area an additional 1/8” is a lot in relative terms. Especially on the walls where it’ll want to ooze down while it’s still wet.

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Old 12-26-2017, 02:42 PM   #6
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Thanks for the input.
I had not heard of nobleseal. You are referring to the thin membrane material? tools4flooring has some. It states that it is 0.03" think. So for a quarter inch buildup, I would need 8 layers of it for 1/4" buildup. They have a 3 foot x 33 foot roll for $117, which should be about enough.

I did a rough layhout like you suggested, mainly to see how the partial cuts on the tile would work out.
I like the idea of laying out and precutting the field tiles first. My concern was accuracy. Would a small hand wet saw be good for cutting those curves really clean? Ryobi has one for about $89 at HD.

So no one has given any thought to using 1/4" Hardie board as a buildup? Is it not feasible to use it like that?
What about 1/4" Durock, instead of Hardie, for the buildup? I think it can handle water getting in it much better than Hardie can.
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Old 12-26-2017, 10:07 PM   #7
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I thought the mosaic was only 1/8” thinner than the field tile. If so, I’d consider installing a single layer of Noblesesl with a 1/4” square notched trowel and mortar. It would build to approximately 1/8”. It wouldn’t be foolproof, but it would be doable.

Please correct me on the thickness difference if it’s not 1/8”.

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Old 12-26-2017, 10:45 PM   #8
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It is 1/8" thinner, yes. The nobleseal states it is only 3 mils think - 0.03 inches. So one layer wouldn't be much of a buildup.
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Old 12-27-2017, 12:06 AM   #9
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You need to add the thinset thickness. Bubba mentioned using a 1/4 inch notch trowel for the Nobleseal which would get you real close to the needed build out. For installing the mosaic, use a smaller notch.
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Old 12-27-2017, 12:41 AM   #10
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Yeah, what Davy said. It would be really close to 1/8" total build up.

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Old 12-27-2017, 09:26 AM   #11
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Thanks everyone for the advice.

I just got a call back from a rep at Georgia Pacific (makers of DensShield), and he told me that using RedGard around the exposed edges of DensShield should seal it against water getting in. So my plan for the extra buildup is to use 1/4" DensShield as a buildup, instead of a mortar buildup. I can use galvanized screws to attach it to the main DensShield board, and then cover those screw holes with silicone/thinset. After sealing the edges of the 1/4" DensShield with Redgard, it will hopefully be nice and waterproof.
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Old 12-27-2017, 09:41 AM   #12
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Tim, unless the rep that told you that is willing to come and repair your failing shower I'd take that advice with a grain of salt...perhaps many grains. I also doubt Custom would give their blessing to what you're describing.

Were it me, I'd want all the materials in the buildup to be waterproof and not rely on edge sealing. In addition, I think you're going to find that buildup of material thicknesses to be problematic by giving you the opposite problem of what you're facing now.

As others have suggested, I'd find a way to build up in situ rather than attempting it at the substrate level.
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Old 01-01-2018, 02:20 AM   #13
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What Peter said.

Densshield, unlike cement boards, is suseptible to deterioration when exposed to moisture. This is a wet area you're installing it in. Please choose a substrate that will not degrade when exposed to moisture.


P.S. You seem to be flip-flopping between 1/8" and 1/4" difference between the field tile and mosaic thickness. In post #8, you clarified that the difference is only 1/8". Why are you trying to build up 1/4"?

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Old 01-01-2018, 07:12 AM   #14
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You don't mention the size of the individual mosaic tiles, but unless they're really small, I'm thinking Ditra might work for that application. It's not like you'll be walking on it, so the point-load argument wouldn't apply here.
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Old 01-01-2018, 12:10 PM   #15
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Who is Ditra Mike?
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