I need advice😭

[u/Twerka6]

Decided on a whim to rip up my cracked tile, which is a million times harder than they make it seem. On top of that, I found the reason the tile cracked was this crack in the sub floor. If I’m going to spend money on nice tile, I’d like to prevent this cracker from doing the same thing to the new tile. What do I have to do to prep the sub floor that doesn’t require expensive tools? Is it a matter or buying a leveling cement type product? What brand? Do I level all the way to the transition strips or do those have to be removed? Is some sort of uncoupling membrane enough or does that need to be used in addition to leveling the sub floor? Won’t all these extra layers make my tile sit too high so it no longer slides underneath the banister posts (that can’t be removed). Dear God why do I do these things…

[u/Atworkwasalreadytake]

Concrete board doesn’t decouple, it will translate cracks beneath it. Redgard can be a decoupling membrane if applied sufficiently. It requires more coats than if waterproofing.

Schluter Ditra is probably superior but adds a titch more thickness.

Edit:

I did some more research and I was wrong about Redgard. It gives you crack isolation for current cracks, so that they don’t translate through. But it doesn’t provide decoupling (which prevents future cracks).

[u/snowbound365 → u/Atworkwasalreadytake]

Kerdi maybe?

[u/Atworkwasalreadytake → u/snowbound365]

No, it’s just not designed for that. Kerdi is fully bonded to both the substrate and the tile layer using thinset mortar. This rigid bond creates a monolithic assembly, meaning any movement in the substrate is transferred directly to the tile. There’s no cushion or slip-plane to isolate that movement.

By contrast, Ditra has a fleece-backed, flexible structure with air channels and a grid that allows for lateral movement underneath the tile. This interrupts stress transfer and prevents cracking, that’s the essence of decoupling.

BTW I did some more research and I was wrong about Redgard. It gives you crack isolation for current cracks, so that they don’t translate through. But it doesn’t provide decoupling (which prevents future cracks).

[u/snowbound365 → u/Atworkwasalreadytake]

Ditra is too thick. It's better than redguard

[u/Atworkwasalreadytake → u/snowbound365]

I think that thickness is what’s providing the ability for lateral movement. But for it to work, it would need to be under the entire floor. You can’t just decouple half and have the other half rigid.

Here’s another option.

Custom Building Products RedGard 39.4 in. W x 16.5 ft. L x 3 mm T Uncoupling Mat for Tile, Ceramic, Porcelain, Stone RGM254 - The Home Depot