Waterproofing options for new shower room

Hi,

A newcomer here and thank you to anyone with the patience to read my drivel.

I am renovating an old stone house, have just finished a kitchen, and now need to install a first floor shower room (1.7m x 2.35m).

The previous owner had the room to a state of green plasterboard walls, and chipboard floor. There are hot and cold feeds to one of the long walls, for a vanity, and hot and cold feeds - and evacuation - to the end wall, for a shower mixer and shower drain.

I have yet to lift the chipboard but think it is installed on very thick (300mm square) beams presumably with shimming.

I want to install a curb less tiled shower across the width of the room (1700mm). This will be partially partitioned by a half-height wall, and a glass screen. I think around 90cm deep leaving 80cm access into the shower. I shall install a vanity along the remainder of the long wall (spanning between the short wall with the door into the room, and the half-height partition wall for the shower). So a simple layout. And I would like to heat the floor and the shower floor. But most of all, I want it watertight!

Cost is always an issue but it is a relatively small room and I am not a pro, so I would rather pay for reliability and ease.

The various systems are driving me crazy and if I watch another YouTube shower video I may lose it altogether 🤣

The main choices appear to be Wedi or Kerdi/Schluter.

My understanding is that I would need to…

1) Take up the chipboard, see what I have, but aim for a level subfloor of 22mm marine ply with the ply dropped between the beams in the shower area to accommodate the tray;
2) With Wedi, panel the shower area and 3ft beyond with 1/2” panels (effectively the whole area as it is a small room) - either over or in place of the plasterboard;
3) Build the partition wall by laminating 2x 1” sheets of Wedi;
4) Deck over the plywood floor with 1/4” Wedi (and plan the shower subfloor so it will still be flush)
5) Install a heat mat on the floor and in the shower;
6) Cover with thinset;
7) Tile floor and then walls.

Have I understood the layers and sequence?
Is Wedi a good option for me or should I be thinking Kerdi/Schluter (I do like the lapping and the reliance of Wedi on caulking seems more error-prone)? Or something else?
Can I apply heat mat direct to the polystyrene shower base?

My thinking is that the Wedi will waterproof everywhere and give me a slip layer above the plywood. I would have no slip layer in the shower but I guess I don’t need one as I am tiling onto the shower tray (over the mat set in thinset).

Thanks for any comments, whether I am on the right lines or missing something vital!
 
The entire floor is level, and you want to create a slope in the shower area? Thought you already pitched down the shower. You will have to rise up the entire floor to be able to get a pitch down in the shower area.
 
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No… the floor is flat, the shower area is already sloped (a wedi riolito neo tray with a linear drain up against the wall).

I am putting a heating mat everywhere, including the shower area. And ideally I will bed it in a thin layer of self leveller. But I don’t want to do that on the shower area because I don’t want to level the slope!

I think the answer is: use self leveller on the flat floor (not to level, just to cover the heating mat prior to tiling) - and don’t use leveller on the tray, just make up the height with thinset. Ideally I don’t want a junction between the leveller and something else -beneath the tiles - but I can’t see a better way.

Someone must have put a mat on one of these trays….?!
 
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Thank you. I already have the mat - but perhaps the answer is to embed in thinset and cover with membrane (wedi do a membrane too), so I have a flat and even surface to tile on. And I can use the same technique on the tray as I am not bothering with leveller.
 
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Embed the membrane in thinset only, make sure it gets a good bonding.
If the membrane is similar to Schluter then it is easy to install the tiles on top following the manufacturer's instructions.
 
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In the end I put my Big Boy pants on, mixed up some rapid setting leveller, waited 5 minutes, poured it, and raked it back up the slope a few times till I was happy it had set.

I have so many layers going on already I decided against membrane. The mat and leveller are on 50mm wedi board so I am happy there is decoupling.

IMG_6204.jpeg
 

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