Laying over Thermal ROCKFLOOR - Tile Advice

[perquafee]

Hi,

This is for a bathroom (including a bath).

I have a buildup of timber joists / 22mm ply / 25mm thermal rockwool batts (with wet UFH pipes running through them). I would appreciate any suggestions on what layer to add next to create enough rigidty to lay tiles.

I appreciate that trying to lay tiles with (relatively) soft wool bats underneath is asking for trouble, but the other layers carry across from the rest of the 1st floor and are in place already. I have made sure the chipboard is plane and level by carefully packing the joists to remove unevenness, so as long as any loads are spread out the wool bats shouldn't deform significantly.

I have two ideas:

1) 22mm screedboard plus a layer of 6mm hardie board attacehd with screws and adhesive to add stiffness. On the rest of the flat I already have screedboard 22mm. This is reasonably rigid, but can flex at joints (and also deforms slowly over time in response to any loads esp. with humididty as the boards are a mix of cellulose fibres and gypsum).

2) Two layers of 12mm hardie board with staggered joints, screws, tile adhesive. This isn't as thermally conductive though.

3) Other suggestions?

(Incidentally, the rockwool batts function to provide both acoustic insulation and as a conduit for the UFH. It works nicely if you can sacrifice the 50mm height)

Thanks for your time.
P

 

[fredbobrichard]

if i understand correctly the insulation is between the joists, pipes above it, and ply on top of that...?
IF the pipes are above the ply on kingspan cut outs i would consider self leveling.
I would be leary of screwing on any material over underfloor heating.
Even without U.H., I always use screws that are not long enough to penetrete out of the floorboards and into any pipes or cables underneath them

 

[Gazolzwurf]

If this is the route you've chosen then you should've used PIR and not rockwool. Good luck easing that door into the room to get over the step 🤣