Tiling over concrete expansion joint

Submitted by Scav54 t3_11bz2e2 in DIY

I am redoing the floor in a small bathroom. Our house was built in 1999 and has a slab foundation in South Carolina. This bathroom has an expansion joint crack in the concrete going straight through the room. I am trying to install mosaic tile and so I can’t use Schluter Ditra (tile less than 2”x2”)

With a 24 year old concrete slab, do I even have to worry about movement in the slab anymore?

Any other option for decoupling membranes that support smaller tile?

Here is a picture of tile and crack https://imgur.com/a/RlPQ6IA

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kittenrice t1_ja0o8rv wrote

I'm not an tile expert by any means, but imo that is definitely going to need to be decoupled.

It's a not a huge sub, but r/tile does exist, try asking over there.

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New_Engine_7237 t1_ja16xiz wrote

Looks more like a settlement crack. I would expect to see a perfectly straight line and expansion joint material in the joint. Too many irregularities in the crack to be made on purpose.

You may find the tile will also crack over time if the slab continues to shift.

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Scav54 OP t1_ja181ij wrote

It has a white plastic strip embedded in it. The irregularities come from Thinset that was used to fill the crack a long time ago it seems.

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New_Engine_7237 t1_ja18ijj wrote

Saw someone else mention some kind of membrane. Not familiar with that although I have seen Mike Holmes use an orange material that gets thinset to the floor then the tile laid on that.

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Scav54 OP t1_ja1a52l wrote

Schluter ditra. Was going to use that but the tile needs to be at least 2x2 which this one isn’t. Might have to change the tile I use

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New_Engine_7237 t1_ja1afy9 wrote

Even if your tile comes on the mesh backing? Doesn’t look like individual tiles.

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zedsmith t1_ja35574 wrote

Both ditra and kerdi board require at least a 2x2 tile to get the warranty from schluter. Both substrates aren’t stiff enough to resist the point load that could result from weight on small tiles.

When you get bigger tiles, the tiles themselves, and the thicker thinset bed, make for a stiffer assembly.

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CyberKingfisher t1_ja0obfz wrote

You should fill that crack, preferably with a polymer-based filler. Then as this is a bathroom, you should have sealed the whole floor with a tanking kit before tiling. That way, if water finds its way through cracks in the grout, it won’t find its way through the cracks in the concrete.

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DavidM47 t1_ja0pyr2 wrote

I think you’re right that it’s a crack.

I’ve never seen such a perfect crack in a foundation before.

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DavidM47 t1_ja0pkth wrote

I would make it the expansion joint in my tile.

Expanse of tile greater than 15-20 feet should have an expansion joint anyway.

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jsar16 t1_ja1joxu wrote

You need and isolation membrane. There’s things like ditra that go over the entire floor, or there is fabric sold on rolls that is around 6” wide and applied to only those areas.

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Kachel94 t1_ja1tkfo wrote

You really need to use a waterproofing system before the tiles.

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tazmoffatt t1_ja23gtw wrote

No uncoupling membrane under that tile?? Yikes

Edit: you said Ditra isn’t recommended for small tile but there’s other options. Green skin, other isolation membranes, add subfloor with DMX and tng osb before tile and tapcon to the floor, etc

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Scav54 OP t1_ja2y4z8 wrote

That’s the way I’ll go, redguard has a system without the size limitation

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Nimrod6979 t1_ja56vf9 wrote

Is that tile recommended for floors? Looks like a wall tile to me and even if it is for floors that’s a lot of grout area to keep clean which is the number one thing most people dislike about ceramic tile….keeping the grout clean

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Scav54 OP t1_ja5ezg5 wrote

It’s marble, a bitch to keep clean by itself :-) works fine for flooring though

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Prcnjfl t1_ja64ad6 wrote

If Schluter won't work, try Widi or equivalent.

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Carpenterdon t1_ja9kg8f wrote

I used red guards decoupling mat under my shower and bathroom tile. It also say "recommended" minimum of 2" but I've had zero issues in 6 years with 1x1 mosaic tile in the shower. Personally I'd take the risk on the smaller tile which "might" be a problem later with cracking grout over not using a decoupler that "will" be a problem over that concrete joint.

The only other option really is to put an expansion joint in the tile. But that is going to be right in front of the toilet where you will feel it all the time with your feet. I'd throw down a membrane and worry about possible tiles moving down the road. Unless you are wearing high heels in that bathroom a lot with a point load on a single tile it's not ever going to be a problem. You'll lose any "warranty" by using small tile but honestly you are putting tile over a concrete slab... Water getting thru isn't really a problem.

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Scav54 OP t1_ja9me0q wrote

That’s what I ended up doing. Was considering doing an expansion joint using silicone but decided to just risk it and deal with cracked grout later if it becomes a problem

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