825x550x20 limestone on underfloor heated suspended 12mm ply

[Fraser]

Hello fellas,

I have a customer wanting to fix 825x550x20 limestone tiles on underfloor heated, suspended 12mm ply floor.
Due to bifold doors, the height is restricted, so cannot overlay ply.
I'm getting mixed advice from tile suppliers, underfloor heating manufacturers, and adhesive suppliers.

There is 55 square metres to be laid.

Questions.

Would cross laid 6mm ply be better than 12?
Would Nicobond "Plastic Ply" solve the problem?
Is ditra matting going to be effective?
Two part Mapei flexible straight on the ply?

At the moment, the best solution is plastic ply with 2 part flex,
but the materials cost is well over two grand.

I have in past tiled on suspended underfloor heated 6mm with two part with 300x300 slate,
and it was fine (not without protest), but would never spec it myself or be held liable.

I am in no way liable for this job if it cracks, but would like to know your thoughts.

Cheers

 

[Ajax123]

Whether you spec it or not if you do it and it is wrong as an expert knowingly carrying out the work incorrectly automatically makes you liable. If you did it in my house i would sue...

do it right or walk away....

 

[Colour Republic]

What are the doors made? and why can't they be cut down?

at 12mm that floor must be bouncing all over the place already, add UFH in the mix and you're asking for trouble IMO

 

[Fraser]

Hello Ajax, thanks for your reply. So you suggest to walk away? Surely a simple letter waiving responsibilty for defects due to movement would suffice in court?
Or do you believe you have a solution to the above problem?
"Do it right" isn't a solution.

 

[Fraser]

What are the doors made? and why can't they be cut down?

at 12mm that floor must be bouncing all over the place already, add UFH in the mix and you're asking for trouble IMO

the idea of tiling it just seems so wrong. The manufacturers insist it works, and as I said, the first one I did had no problem on a floating 6mm with Keraquick and latex.
I was amazed it stayed down. I told the customer it would definetly fail too!

 

[Bubblecraft]

Can the bi-fold doors be cut or swung into the adjacent room giving you plenty of height to work with?

I wouldn't go straight onto 12mm ply. As said above, it must be bouncing all over the place. I'd overlay with Hardibacker 500 or at least 10mm insulation boards such as Warmup or thermal Aquapanel with SPF & screwed then work from there. Don't try & compromise with what you've got. Do it right first time wither your liable for it or not. It's good practice. Explain to the customer what is required & why.

 

[DHTiling]

No waver will get you out if it, if the floors fails and you knew it would but still tiled it then you are in the wrong, no matter what piece of paper gets signed if you know what you are doing is not to spec then you are to blame. simples..

12mm sub-floor... jeez what numpty put that idea to the customer..

 

[John Benton]

Hello Ajax, thanks for your reply. So you suggest to walk away? Surely a simple letter waiving responsibilty for defects due to movement would suffice in court?
Or do you believe you have a solution to the above problem?
"Do it right" isn't a solution.

Do it right, do it once.

 

[Colour Republic]

Are you seriously saying that you tiled a floor that had 6mm ply directly fitted to joists, then ufh, then 300x300 slate and it all stayed put??

 

[nybor62]

imho if u fix limestone to that substrate within months it will end up looking like crazy paving cracks every were

i understand your dilemma , explain to the customer the pit falls of poor prep work or failure is a cert esp with lime stone

 

[Fraser]

Are you seriously saying that you tiled a floor that had 6mm ply directly fitted to joists, then ufh, then 300x300 slate and it all stayed put??

yeah, spoke to the customer 6 months ago, and apparantly its still fine, about 50 square metres of it, a games room, theyve even got a pool table standing on it.

 

[Fraser]

Well just been to site to find the builder pulling his hair out, a clueless customer, and a what looks like half a spec from the wet system manufacturers.
Told the customer to consider an undertile electric system, as the wet system wasnt going to work.
Not what he wanted to hear, but understands the consequences of the floor failing.
Will wait to hear the outcome, and let you guys know.

 

[John Benton]

Are you seriously saying that you tiled a floor that had 6mm ply directly fitted to joists, then ufh, then 300x300 slate and it all stayed put??

The joists are 10mm apart so its ok

 

[Colour Republic]

Hang on Fraser could you tell me the spec of the floor... so this is wet ufh?

 

[Bubblecraft]

I was also under the impression it was loose wire of matting system