Tiling Advice Wanted - Over Wet UFH

[swampie]

Great thank you all very much indeed. You have been a great help to me and probably have just saved me a right proper ball ache in the future.

I've been told to use a C2 S1 adhesive, I've also been told to use a high temp adhesive, is there a product that mixes all properties available on the market? If not, what have you used Bri as I'm sure that you seem to have your head round the same type of project at the moment🙂

Sorry, just re read and seen Ajax's Sika reccommend 🙂

 

[Ian]

That job was 12 months ago, I only used an SPF, weber I think it was, grey to stick the hardiebacker, white for the tiling.

 

[mike1979]

Ardex x7 is good stuff but any decent SPF will
do the job

 

[Ajax123]

Considering my floor construction and not wanting to raise the floor level, I wanted to install the UFH between the joists.

The decision to use this mix was made after several UFH suppliers confirmed that this system was the best U-Value compared to the metal trays which are already routed out for pipework and was the only other offered by my supplier without raising floor levels.

UFH companies don't really push this system as they'd rather you bought the products but trust me it works so far & I'm sure the tiles will warm. The system so far has been on for months now. It is nice and warm underfoot.

I have already finished the bathroom and in fairness, the tiles are not warm to touch before the room is up to temp, but that is a small room and heats easily. My kitchen may well require a higher heat.

See the design here

I agree that the reflector plates are not great in terms of thermal mass but a proper screed either sand cement or better still anhydrite compacted over the pipes between the joists is a far better option. cracking is not important as there is a rigid final floor to go over the top of it ie floorboards or similar.

Problem with a biscuit screed is that there is a lot of air trapped in it. Obviously, if i read it correctly, this is already installed o too late to change but might be worth knowing for future reference. To be fair I did precisely the same thing in my attic room and I find it pretty difficult to get it to generate much warmth. I used anhydrite downstairs and I find the opposite down there. I struggle to keep it cool enough. It is only ever set to 1 on the thermostat.

 

[swampie]

I agree that the reflector plates are not great in terms of thermal mass but a proper screed either sand cement or better still anhydrite compacted over the pipes between the joists is a far better option. cracking is not important as there is a rigid final floor to go over the top of it ie floorboards or similar.

Problem with a biscuit screed is that there is a lot of air trapped in it. Obviously, if i read it correctly, this is already installed o too late to change but might be worth knowing for future reference. To be fair I did precisely the same thing in my attic room and I find it pretty difficult to get it to generate much warmth. I used anhydrite downstairs and I find the opposite down there. I struggle to keep it cool enough. It is only ever set to 1 on the thermostat.

Good comparison Ajax, yep it's too late and all you say sounds like it must be true. The weight of the wet screed had me concerned to be fair. In my Kitchen I had 5" Joists and was not confident they'd take wet over a long time.
Now you say that though, I wish I'd got wet.

I will definitely consider the wet mix next time🙂 This was my 1st ever wet install, there's a lot to learn, piece of cake once you've done one though.

 

[swampie]

Oh and as for Anhydrite, I have never heard of it.

I do hope I get the kitchen and hall warm enough now you've said that. It'd be a poor doo if I end upo needing a radiator.

 

[swampie]

So from here on in:-

* lift the ply
* install 6mm backer board on using 6mm notched trowel bed of C2 S1 adhesive (Hardie says 6mm)
* install Ditra 25 on 3mm notched trowel of C2 S1 adhesive (Ditra says 3mm)

*What bed is best thin bed for the 600x600x15mm Marble tiles? (Ditra says thin bed but which?)