Tiling Advice Wanted - Over Wet UFH

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Tiling Advice Wanted - Over Wet UFH

Discuss Tiling Advice Wanted - Over Wet UFH in the Australia Tiling Forum area at TilersForums.com.

S

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.​
 
S

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?
 
Last edited by a moderator:
S

swampie

Ajax123 said:
Why a biscuit screed?? it will hardly get warm with all that stuff on top...
Click to expand...
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
 
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I

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
0a8a3c44f4f262ec57f19829ed465924.jpg
2e0263a542be49fefaa0ab06e861a53a.jpg
 
S

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 :)
 
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A

Ajax123

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swampie said:
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
Click to expand...

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.
 
Last edited by a moderator:
S

swampie

Ajax123 said:
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.
Click to expand...
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.
 

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