Wetroom floor, hardi backer already down, needs levelling, uncoupling membrane? - Tile Advice

[Scott HAZARD]

Hi all, starting a wet room floor soon, have a few questions I would like some help with!

The floor has already been installed by a builder and has Hardi backer boards down, running up to the tray, but will need levelling before reaching it.

1. Hardi backer is not waterproof, so how does self leveller fair with it? I will also be priming the boards first with SBR before it goes down.

2. Marble is going down on top, Is an uncoupling membrane necessary as hardi backer is dimensionally stable? Am I being over cautious, suppose it's better to be over cautious and always use it when laying stone?

3. Will be tanking, using the Ardex WPC kit, seen it mentioned that it will effect the weight bearing capabilities of the walls (they are cement boards too), but seen nothing to back this up, anyone know of the capabilities of it, when applied?

Thanks in advance.

 

[Flintstone]

For me- level over the hardie, tank, then tile
The tanking kit will not alter the Weight limit of the substrate it is going on to.
I would only uncouple if it was having under floor heading

 

[Scott HAZARD]

Cheers, appreciate it!

 

[Flintstone]

Is it having underfloor heating? If not, why not? I always recommend it in wet rooms

 

[Scott HAZARD]

Unless it's been installed underneath the hardi backer, I will ask now. The boards have been installed by a builder.

 

[Bathfix Bob]

Highly unlikley theres UFH under there! wouldn't be working after all the hardie screws.

 

[Old Mod]

You should always uncouple stone imo, esp marble because of the fissures in the stone.
If the floor is flat and tileable with just the hardie,
You could latex only where necessary, and forget the tanking to the floor and use properly taped Ditra as a waterproof membrane and run it 100mm up the wall to provide a waterproof skirting too.
So you have a completely waterproof floor and your stone will be uncoupled.
Obviously the walls will still need tanking.
If you tape Ditra to make it waterproof, you're required to use Schlüter's Kerdi Coll adhesive.

 

[Scott HAZARD]

Thanks for the replies, I used a membrane in the end.