Wet underfloor heating upstairs

[mrbenn]

Hi,

I'm scratching m head knowing what to do for the best with this floor. I'm a self builder, and I didn't think that tiling the bathroom would turn into one of the most technical aspects of it I wanted to construct a wet room, we're using 12mm marble on top. The underfloor set up is 50mm kingspan between the joists, pipes clipped to it and 30mm screed to bring it to the top of the joists. This provides quite a stable base, but is liable to the odd crack here and there. I am then wondering what to put on top. Current thinking is 12mm wbp ply and 12mm hardibacker, set on with tile adhesive. then some of the durbase ci++ decoupling stuff, taped. 12mm hardibacker 1.2m up the wall, and around the shower, moisture resistant plasterboard elsewhere else. Thinking of using an aquapanel shower tray. I am concerned about the floor build up... all that lot comes to about 45mm, which makes it an inch higher than the adjoining flooring, which is 20mm thick off the joists. There are lots of thinner products out there... but most seem to be insulated, meaning they're not the best with wet UFH.

Anyone have any better ideas?

Thanks,

Sean.

 

[One Day]

You've gone too far now to use Bekotec Therm from Schluter.
It would have ticked ALL boxes in one easy go.
From the suggested plan I would strongly suggest you get an expert's advice.
HB 1.2m up the wall and MR plasterboard will NOT make a wetroom.
Well, actually you will end up with a wet room and maybe a wet room below!

I would be inclined to use 12mm HB on the floor, bonded with tile adhesive and screwed into the joists. Ditra on top (I don't trust Durabase).
Waterproof the ditra joints using tape and Kerdi-col.
As for the tray, if you really want the heat to reach the tray then opt for an Impey tray.
Either board the wet area walls with a proper WATERPROOF board like Kerdi Board or Wedi / Marmox / Jacko and waterproof & tape all joints and fixing points using Ardex WPC or simply use plasterboard and waterproof it all with Ardex WPC.
Please take extra care at all internal corners. Don't scrimp on waterproofing!

 

[mrbenn]

Thanks for the reply impish, very helpful.

You've gone too far now to use Bekotec Therm from Schluter.
It would have ticked ALL boxes in one easy go.

Looks like a simple system, bit late now I suppose Might have added too much cost into the setup. 80% of the upstairs is engineered oak flooring, which I guess might not have benefitted as much as the bathrooms.

From the suggested plan I would strongly suggest you get an expert's advice.
HB 1.2m up the wall and MR plasterboard will NOT make a wetroom.

I guess it depends how wet you expect the room to get. I was initially planning to use a fleece on the wall surrounding the shower, bath and basin, taped.

Well, actually you will end up with a wet room and maybe a wet room below!

I would be inclined to use 12mm HB on the floor, bonded with tile adhesive and screwed into the joists. Ditra on top (I don't trust Durabase).

I was planning this, but I spoke with Hardi tech support, and they told me that 12mm HB was not considered structural, and would need something like ply to support it. The existing screed is pretty firm, but it does flex in places. It's only 30mm thick, and moves a little when walked on.


Waterproof the ditra joints using tape and Kerdi-col.
As for the tray, if you really want the heat to reach the tray then opt for an Impey tray.

Not so worried about heat under the feet in the shower, so I was thinking about one of the aquafix shower trays from the pure adhesion website. They look OK cost wise, and the traps supplied are high capacity types. We have mains pressure hot water, so a good trap is important.

Either board the wet area walls with a proper WATERPROOF board like Kerdi Board or Wedi / Marmox / Jacko and waterproof & tape all joints and fixing points using Ardex WPC or simply use plasterboard and waterproof it all with Ardex WPC. I will investigate waterproof board for the high moisture areas.
Please take extra care at all internal corners. Don't scrimp on waterproofing!

I had some Larsen fleece preformed corners donated to me, I was hoping to use those in the corners. Is there a decent wall board that CTD stock?

Thanks

 

[Sean Page]

Sorry, wrong thread, oops!

 

[One Day]

Thanks for the reply impish, very helpful.



I had some Larsen fleece preformed corners donated to me, I was hoping to use those in the corners. Is there a decent wall board that CTD stock?

Thanks

Pre-formed corners are great, yes use them!

CTD stock a trade board, I think they call it "contract" board (made by Jackon)
The price is great so I'd recommend them, and grab am Ardex WPC kit too for waterproofing the joints and fastener heads as well as fixing in your corners.

 

[AliGage]

I use the CTD board. Its really good and cheap in comparison

 

[Ajax123]

Hi,

I'm scratching m head knowing what to do for the best with this floor. I'm a self builder, and I didn't think that tiling the bathroom would turn into one of the most technical aspects of it I wanted to construct a wet room, we're using 12mm marble on top. The underfloor set up is 50mm kingspan between the joists, pipes clipped to it and 30mm screed to bring it to the top of the joists. This provides quite a stable base, but is liable to the odd crack here and there. I am then wondering what to put on top. Current thinking is 12mm wbp ply and 12mm hardibacker, set on with tile adhesive. then some of the durbase ci++ decoupling stuff, taped. 12mm hardibacker 1.2m up the wall, and around the shower, moisture resistant plasterboard elsewhere else. Thinking of using an aquapanel shower tray. I am concerned about the floor build up... all that lot comes to about 45mm, which makes it an inch higher than the adjoining flooring, which is 20mm thick off the joists. There are lots of thinner products out there... but most seem to be insulated, meaning they're not the best with wet UFH.

Anyone have any better ideas?

Thanks,

Sean.

how is the insulation and screed supported from underneath?? How much deflection is there...

 

[mrbenn]

It's only supported on two rows of slate battens, and although it doesn't move much at the moment, I wouldn't like to rely on it.

As I'd already bought a roll of Durabase CI++, I emailed Dural tech support, who told me 18mm ply was the best option, to use their sealing tape, but told me to seal it using a 2 part product, like , Schomberg TC-07.

As I couldn't find this, or anything like it, I swapped to Ditra matting, with all their Kerdi tape and sealing glue. I also spoke to Schluter tech support, who told me 18mm ply was the way to go, so thats the plan.

Here is the floor construction, as I explained to Dural tech support.

View attachment 58871
Bit small, but you I hope you get the idea.

As Impish suggested, I've decided to use the CTD contract board and Ardex WPC, because I'm paranoid!