Ok here is one for any tile experts out there. I have an existing building with conrete floors. In the area framed out for a new bathroom there are two seperate slabs dividing yhe room nearly in half. One of the slabs sits anywhere from one inch to inch and a half higher than the other. To put he floors on the same plane I put down plastic to act as a bond break on the lower slab. Then I proceeded to put down wire lath then my 2pt sand 1pt portland morter bed. After a day the bed is lifting on the front corner where the bed is thinnest 1″. Not cracking but almost floating up if that makes sense. Where did I go wrong. I’m assuming I should not have used the plastic. I was just worried about the mortar bed moving with the existing slab. Any advice would be greatly appreciated. Thanks Scott
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You went with a floating thin slab, and it curled because the top dried out faster than the bottom that sits on the plastic.
It seems to me that you should tear out the thin slab and replace it with a thin slab bonded well to the underlying concrete. The joint in between the two slabs will likely move an unknown amount. The movement can be restricted somewhat by inlaying rebar epoxied into saw kerfs bridging the two slabs, but you will still want to apply a slip sheet over the floor before setting tile.
Bill
Thanks Bill for the input. Can you explain what a slip sheet is? Are you talking about Ditra? Or something else. Thanks
A slip sheet is a layer of flexible material bonded in between the ceramic tile and the underlying substrate to prevent movement in the substrate from telegraphing through the tiles. Ditra is one product designed to do this, among its other functions. There are many other products that also function as slip sheets.Bill
2:1 that's a pretty fat mix for a shower floor, try 4:1. I'd chip down the high slab so it's a slope and not a step. Paint with concrete weld and level the area with patching cement, then build your mortar bed- 30lb felt, diamond lath, 4:1 mix pre-slope, membrane or pan, etc.
Misting the patch and bed 1x or 2x during the cure will help reduce curls and cracks.
YMMV
Jim
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Your minislab is warping because it dried on top while still wet under at the plastic. If you had covered with more plastic for three days, it would not have happened.
2:1 is pretty rich. That makes it more brittle for a thin patch. i'd be using 3:1 or 4:1
At that sharp drop, I would chip off the edge with a demo hammer. Having it sharp, makes it act like the perforated line in tear off paper. cracks happen there easier.
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What Bill & Piffin said. Chip off the edge and lay in rebar between the two. And yes, your mix was way too rich.
I would drill, lay in the rebar and then throw in some mix over the bar, then lay in your diamond mesh over everything and throw your floor.
The mix is way too rich.
here's a link covering the process-
http://www.johnbridge.com/deckmud.htm
He advocates 5:1
Henley thanks for the link. It was helpful. Also thanks to everyone else who gave input. Much appreciated. - deliamey