To Ditra or not to Ditra...

[johnryan]

your not wrong about that. it's tough call to make, but the way i see it, is that if the manufacturers of stone products recommend something, and most tilers i know say the same, i'd be wary of trying anything different. hope it all goes well for you anyway.

 

[The Legend; Phil Hobson RIP]

I would go with Stewart and Doug

 

[Stewart]

Just out of curiosity....... what did your 4 tilers say about the 12mm ply?

 

[HimediA]

What's the width and length of the room?
Edit: found it ignore that.

I'd have said the floor is big enough to warrant using a decoupling membrane (Dural not Schluter mind) to be fair.

Though without looking at it and testing for deflection nobody could guarantee either way.

Thanks Dan. What would a typical deflection test comprise?

And is the use of a membrane due to length of room and lateral movement (expansion/contraction I guess?), or is the robustness of the sub-floor and vertical deflection the issue?

If the latter, I confess I don't see how a flexible membrane will really help (although that's my engineer's training and not stone flooring expertise so I stand to be corrected!)

If the former ie. horizontal movement as opposed to vertical, is that really likely to be a risk given no underfloor heating?

And all you experts please understand I'm not doubting your expertise, it's just my darned questioning engineer's mind....

 

[HimediA]

Just out of curiosity....... what did your 4 tilers say about the 12mm ply?

Two said would have preferred to see 15mmm but 12mm should be OK
All said should be fixed down at max 150 centres.
Three said make sure it's sealed (one with tile primer one said SBR fine, one advised PVA fine)
None came up with Stewarts suggestion of thinner backer board & Ditra.
It's a minefield out here gents...:mad2:

 

[Gazzer]

The main point is assessing the deflection that is there.
I personally would go on how it felt as i walked across the floor. There was a old story we used to hear that if a pint glass of water was filled to the brim and then you walked around the glass 1m away. If any water ran down the side of the glass the floor had too much deflection........I also heard that if it didnt , that you should walk heavier !!!!

 

[HimediA]

'The old ones are the best'... but that is at least a demonstrable test! I'm now anticipating the look on my wife's face when she sees me walking around a glass of water on the floor. She'll think I've listened to her at last and it's some AA mantra thing...
Now I wonder, will my 16 stone bulk be sufficient or should I strap a few 600 x 400 slabs of the appropriate flooring limestone to my back...:lol:

 

[HimediA]

What's the width and length of the room?
Edit: found it ignore that.
I'd have said the floor is big enough to warrant using a decoupling membrane (Dural not Schluter mind) to be fair.
Though without looking at it and testing for deflection nobody could guarantee either way.

Now Dan you're trying to confuse me... :yikes: what is the difference? performance? price? other?

 

[Stewart]

Schluter and Dural both perform the same. As a recent convert from Schluter to Dural, I've found the only difference is price, with Dural coming in much cheaper.

 

[johnryan]

i think the ditra matting transfers the downward stresses to whatever is below it, and reduces the stress on the tiles somehow. it's not just lateral movement it counteracts, but vertical too. at least that's how i thought it worked.