70m2 Floor, 2 substrates, Ditra and Hardie?

[clipboard2008]

Hi

I have a client who needs me to tile his kitchen. Part of it is caber floor T&G (original part of the house) the other part (extension) is sand and cement screed. The extension comes off the front and side of the house so the join between the timber and screed is in an L shape. There is also wet underfloor heating under all the floor.

Tiles are 600x600 Porcelain

How is the best way to stabilise this floor?
The client doesn't want an expansion joint over the join in the 2 substrates as it would be in an L shape and ruin the look of the tiles

Is it going to be a case of fixing Hardibacker across the whole floor, bridging the join then covering in ditra?
Would this stabilise it enough to ensure no future cracking?

TIA

 

[Dumbo]

Biggest question is the caber floor floating or fixed to joists .

 

[clipboard2008]

Fixed to joists, though there is some flex at joint between timber & screed

 

[Flintstone]

That is the question, what is the underfloor heating system set up on the wood side ? If you are over boarding with hardie, you shouldn't need ditra, imo! But an anti fracture mat over the area where your bridging the two substrates wouldn't hurt.

 

[Flintstone]

It's the flex at that point that will likely cause problems.

 

[Dumbo]

If you can see it flexing you got problems possibly with the suitability of the timber floor for tiling . Just to be clear does it have ufh on timber floor .

 

[clipboard2008]

UFH is under the caber flooring and is also in the screed.
On the timber side it is polypipe laid in a metal tray then sand cement to top of the joists so heat transfers to caber flooring.

 

[Chris Gibbs]

in my opinion don't use ditra... sorry, but it doesn't stick to the matting that well for me to have piece of mind. some may disagree, that's my opinion and experience. id go for a durabase dural matting...

 

[Dumbo]

I think you need to set your tiles out in both directions that joint is on substrate change and use dural microjoint or coloured Silicon instead of grout .

 

[GoneGuy]

How big is the area with the caber floor? Is there a possibility of filling it in? To prevent any bounce as that is where your going to coma across with problems

 

[LM]

I think you need to set your tiles out in both directions that joint is on substrate change and use dural microjoint or coloured Silicon instead of grout .

That would be my first thing to check.

 

[LM]

How big is the area with the caber floor? Is there a possibility of filling it in? To prevent any bounce as that is where your going to coma across with problems

That is also an equally important consideration imo.

 

[Dumbo]

How big is the area with the caber floor? Is there a possibility of filling it in? To prevent any bounce as that is where your going to coma across with problems

How do you mean as there is ufh under timber . Do you mean take out floor and screed

 

[GoneGuy]

How do you mean as there is ufh under timber . Do you mean take out floor and screed

Yes thatnis what I was trying to say but without pictures it’s hard to gauge, maybe pump a liquid screed ?

 

[Dumbo]

Yes thatnis what I was trying to say but without pictures it’s hard to gauge, maybe pump a liquid screed ?

It would be hard as you would have to get a Dpm in there . I would say remove flooring , joists and ufh before digging out then starting to put things back together .

 

[clipboard2008]

The underfloor heating is already installed by the builder between the joists. It is set in a tray which is then filled with screed to transfer heat. It's quite popular as it allows you to put underfloor heating on second floors. This is obviously a ground floor.
Certainly can't fill underneath the caber flooring.
My plan is to hardie backer the floor then ditra matt it. I know it's a costly option but it's the only way I can see of ensure it's stable enough so it doesn't crack?

 

[Dumbo]

The underfloor heating is already installed by the builder between the joists. It is set in a tray which is then filled with screed to transfer heat. It's quite popular as it allows you to put underfloor heating on second floors. This is obviously a ground floor.
Certainly can't fill underneath the caber flooring.
My plan is to hardie backer the floor then ditra matt it. I know it's a costly option but it's the only way I can see of ensure it's stable enough so it doesn't crack?

I wonder how many builders get structural engineers calculations on that before loading the joists up with screed

 

[Spare Tool]

The problem you've got here is no...or should I say not many 😉 tilers on here will give you advise to just uncouple and tile over two substrates without following the joint directly through into the tiles, had this dilemma with customers before and tiles have cracked (I told em so 🙂) then again some haven't.
I've used Silicon to adhere tiles across a joint before on a job that had cracked to remedy and it worked , used marmox boards plus a crackmatt only this year as a customer didn't want a dodgy shaped concrete to wood expansion joint in her floor and up to now its been fine, there is no defining answer, you won't get any guarantees off anyone unless you do it by the book, otherwise its a gamble and I'm afraid your stuck between a rock and a hard place with this one.

 

[Spare Tool]

@Tony73 what part of that do you disagree with?

 

[Bond]

The underfloor heating is already installed by the builder between the joists. It is set in a tray which is then filled with screed to transfer heat. It's quite popular as it allows you to put underfloor heating on second floors. This is obviously a ground floor.
Certainly can't fill underneath the caber flooring.
My plan is to hardie backer the floor then ditra matt it. I know it's a costly option but it's the only way I can see of ensure it's stable enough so it doesn't crack?

If there is access and enough space in the sub-floor area, you could add beams or other support to the floor joists.