How to approach this wetroom floor...

[Workerbee]

Hello! I'm turning my tiny bathroom into a wetroom and I had a couple of questions I hoped you guys could help with. Current floor is concrete slab, with 50mm EPS then chipboard, and previously had a shower cubicle with raised tray. I'm taking it back to the slab and hope to put a wetroom shower former where the shower tray used to be, electric ufh and stone tiles. 

 

First question is about supporting a wetroom shower former and floor tiles on a floating floor.

Having done research and spoken to insulation and shower tray manufacturers, I've got a few possible solutions I want to run past the forum:

1) Phenolic/PIR insulation (preferably 75mm), then cement board (22mm?) - insulation manufacturer thought this would be fine to tile on, and would be my preferred option insulation-wise, but I'm aware tilers sometimes say tiling a truly floating floor isn't a good idea. I'm also unsure how I would then install the shower former, as I presume it couldn't just rest on insulation.

2) XPS tile backer board - maybe 90mm for most of the floor as I could do away with the chipboard. Leave a rectangle out for the shower former, and drop in 30mm XPS then 38mm screed, then place the 22mm former on top to bring it level with the rest of the XPS floor. Advantage is better compressive strength with XPS and it could be stuck to the slab, so creating a more mechanical fix between tiles and slab than a usual floating floor. Worse insulation, though.

3) Phenolic/PIR fitted between wooden joists screwed directly to slab, mimicking floor joists that the shower former could slot between. Advantage is high strength; downsides are large thermal bridges throughout the floor, and wood in a wetroom floor, where it could rot.

 

Second question is about how to deal with the current shower tray slab and drain. I've attached a few pictures.

Where the raised shower tray used to be, there is a horseshoe-shaped concrete slab on top of the concrete floor slab, that came level with the insulation and chipboard on the rest of the floor. I'm thinking I should chop this out with an angle grinder and start again from the floor slab, using one of the above floor buildups. The drain is resting on sand, as there is no slab in this part of the floor. Can I keep it like this and just connect into the existing drain?

 

Thank you for any advice. 

[Workerbee]

I'm now wondering if I can do a hybrid option for supporting the tiled floor and shower former. Could I get the best of both insulation and support by having eg 40mm phenolic then a thick XPS board eg 30mm on top that I could tile on to? And for the shower former just have XPS underneath (50mm?) and miss out the screed, to maximise the insulation?

[Nickfromwales]

You only really need a minimal thermal break here, so just use a Wedi wet room former here and kill all the birds with one stone. 
Excavate the whole area, enough to get 20mm Wedi insulation board down plus your tiles and adhesive, and set the Wedi former the same level as that, and then tile across the lot.

 

Make up the deficit at the tray area with layers of 6mm or 10mm Wedi board as required, to get the former at the right height.

[Nickfromwales]

 

Over timber on this job but same principal. 
 

Then cover the rest of the floor so it looks like this. 
 

 

Then when tiled…

 

 

Bingo. 
 

This had electric UFH too, so you can fit that if you want some additional comfort but you shouldn’t really use that for ‘central heating’ of the room (but you can).

 

[Workerbee]

Thank you very much for this, @Nickfromwales - that's very useful.  So it sounds like xps tile board is best for stability for the whole room, (ie under the shower former and everywhere else, for tiling on to). I can stick the xps to the concrete slab and it will help eliminate the floating floor issue.

 

Can I increase the thickness without losing stability? The room previously had 50mm polystyrene and 22mm chipboard, so I've potentially got around 75mm to play with and I'm concerned 20mm wedi board wouldn't be a lot of insulation. Or could I potentially use phenolic/PIR underneath then a thick layer of wedi board on top? 

 

Thanks again!

[Nickfromwales]

7 hours ago, Workerbee said:

Thank you very much for this, @Nickfromwales - that's very useful.  So it sounds like xps tile board is best for stability for the whole room, (ie under the shower former and everywhere else, for tiling on to). I can stick the xps to the concrete slab and it will help eliminate the floating floor issue.

 

Can I increase the thickness without losing stability? The room previously had 50mm polystyrene and 22mm chipboard, so I've potentially got around 75mm to play with and I'm concerned 20mm wedi board wouldn't be a lot of insulation. Or could I potentially use phenolic/PIR underneath then a thick layer of wedi board on top? 

 

Thanks again!

Wedi / Jackoboard etc comes in various thickness, so just max out to suit. 
 

TBH once you’ve thermally broken the floor, adding another 20mm or so won’t make a huge difference, but if you’re happy to dig it out further then more is better obvs. 
 

Just don’t allow the tile adhesive to come through at gaps, eg where the boards butt up to each other and around the edge, use CT1 to fill the gaps during laying so that you don’t get the cold bridge from adhesive. 

[Workerbee]

Brilliant, thank you! Just one other thing - the slab finishes short of the wall and the waste is currently bedded on sand (I think there's a dpm under the sand). Am I okay to leave this as it is and just lay the wedi boards across, notching the underside to accommodate the waste pipe as it rises through the floor? Or should I provide more support for the boards?

I will remove the u-shaped concrete that's sitting on the slab and which supported the old shower tray, and replace it with wedi as you suggested.

 

And should I replace the waste to use new plastic, or is the old okay?

 

Thanks again - I feel I know where I'm going with this now!

 

 

[Nickfromwales]

Can you do a sketch of how the room will be laid out? Eg choose a former, where’s the waste outlet on that former  etc etc. 

[Workerbee]

Yes, I can put something together. Given that the shower was going in the same location as the old one, I'd just been intending to find a former that could accommodate where the waste currently was, but I guess it could be moved and I could cut into the slab to fit it.