Tiling Advice Wanted - Over Wet UFH

[swampie]

Hi All,

I have some 600x600mm Marble tiles to lay over an underfloor heating system and would like advice on adhesives and fitting please?

Floor Construction​

• 
  [*=2]220mm Suspended timber floor joists - ***New build and pretty level***
  [*=2]Batons supporting 100mm Rigid Insulation Board between joists (set 25mm below joist top)
  [*=2]16mm UFH Pipe clipped to insulation Boards
  [*=2]Dry Biscuit Mix Screed, around pipework & leveled to joist top
  [*=2]22mm Moisture Resistant Chipboard
  [*=2]9mm Ply Screwed every 150mm
  [*=2]Kitchen Floor

​

So, what is the best method of fixing tiles to the ply to avoid cracking and lifting, I understand a flexible adhesive is needed but after reading some manufacturers fitting instructions, some are only good for tiles up to 100mm, some are super-flex but don't mention UFH applications. It's becoming a minefield of over-information.

Please help, this job means a lot to me.​

 

[Qwerty]

I wouldn't tile that

 

[Andy Allen]

Im out...!!!

 

[Rookery]

You have a combination of a timber floor, UFH, 9mm ply and a soft stone. It's a recipe for disaster which is why the suggestions so far have been to avoid the job.

 

[swampie]

It's going to be pretty tough to avoid, it's my house and it's also my kitchen, it needs tiling really.

Would you all be suggesting it'd be a nightmare job if I'd got hardie board instead of ply?

 

[Ian]

If I were to tile this floor I would be fitting hardiebacker over the chip board, then ditra ontop of that, then tile.

 

[Rookery]

Agreed.

 

[Just Rizzle]

31mm of heat resistant wood
my advice bin the marble tiles the product I would lay would be karndean or amtico

 

[Dave]

This would have been an ideal product if you had researched further >>> http://www.jameshardie.co.uk/hardiefloor

 

[swampie]

Thanks for the tips guys, I wish I had researched more earlier David but I'm now where I am unfortunately but at least I haven't laid them yet.
Yes that structured floor looks just the ticket, wish I'd got that down.

Ray, those are well worthy of further research, thanks for the tips. I'm not sure it'd beat the real thing though, these 600x600's are nice and will last "if laid correct". I'm scared of marking Vinyl.

So if I do tile, is keeping the ply better than removing it, when considering the advice of adding hardie backer and Ditra?

Is ply so bad? My joiner insists its the way to go. For future reference, never ply even without UFH?

ps My tiles are 600x600x15mm. Will the height make any difference to your opinions?

 

[swampie]

31mm of heat resistant wood
my advice bin the marble tiles the product I would lay would be karndean or amtico

Just spoke to a friend who lays vinyl floor and he also says the Karndean and Amtico have been known to fail as the heat melts the glue on occasions so I've a risk either way.

 

[Ajax123]

Why a biscuit screed?? it will hardly get warm with all that stuff on top...

 

[Ajax123]

you could use a high temperature adhesive. There are quite a few available these days from the likes of Sika and others.

 

[swampie]

Why a biscuit screed?? it will hardly get warm with all that stuff on top...

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

 

[mike1979]

Do as bri says take the ply board up and use a decent tile backer board laid in flex adhesive and screwed down then a uncoupling membrane on top should be fine to tile I use nicobond matting as I find it fairly thin and easier to use

 

[swampie]

Do as bri says take the ply board up and use a decent tile backer board laid in flex adhesive and screwed down then a uncoupling membrane on top should be fine to tile I use nicobond matting as I find it fairly thin and easier to use

Who supplies the nicobond Mike? I can't find any suppliers. Will my builders merchant stock it?

 

[swampie]

I understand the decoupling membrane now but what exactly does the backer board bring to the party that the ply is lacking?

 

[White Room]

Hardie dos'nt get affected with moisture...

 

[Ian]

Backer board won't expand and contract like the ply with the heat from the floor, plus, it's stuck to the substrate as well as screwed adding a little more in the way of rigidity (hardie will tell you it adds no strength but, those who use it know that it does [emoji106]) here's a couple of pics of an identical arrangement to yours except the tiles are limestone

 

[mike1979]

I buy it direct from nicobond I just prefer it over other membranes but I don't want to start a debate on it with others please I know what your all like !!!

 

[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?)