Ditra Matting On Part Of A Floor

[Stu Lilley]

What's wrong with tiling straight on to the screed floor why does everyone want to use ditra all the time it just over complicates things you never herd of 5 years ago never used it never will and if every floor I tiled in the last 30 years was only 6 mm out I would be well chuffed

 

[Stu Lilley]

All floors expand and contract new or old and using Ditra is def not complicating things.. Since the development of thin set adhesives decoupling Is a must ... i have been using ditra for approx 20 yrs now... Surly it makes sence to protect your work from cracking... You would not lay a decent carpet and say no to the underlay as it complicates things

 

[SJPurdy]

All floors expand and contract new or old and using Ditra is def not complicating things.. Since the development of thin set adhesives decoupling Is a must ... i have been using ditra for approx 20 yrs now... Surly it makes sence to protect your work from cracking... You would not lay a decent carpet and say no to the underlay as it complicates things

I think this is overstating things a little, it sounds like a salesman's spiel. There are many circumstances where using Ditra or similar uncoupling layer should be used but to say it is a must for all floor is overstating it I think. All floors expand/contract with heat as do the tiles but the relative difference can be taken up in the floor structure without cracking the tiles. Even my own badly done (before insulation boards readily available) electric heated kitchen floor direct onto a concrete slab which must have a large temperature difference between the top (tiling layer) and the bottom of the concrete hasn't shown any signs of cracking.
I don't really see how thin set adhesives is much different to the previously used cement bonding layer on top of a screed - admittedly usually the screed itself was debonded from the concrete base (building papers/polythene (in my experience) or as stated earlier a layer of sand in older structures); so tiling a screeded floor with thin set is presumably alright (if it wasn't just about every tiled floor would be cracking!).
The carpet analogy is not really relevant because the customer can feel the difference in the softness of the floor as they walk on it; whereas they take a lot of convincing that the bit under the tiles that they can't see or feel is worth £x even when you are explaining that there is some risk of cracking with their floor structure that can be reduced by using. (Note I say "reduced" to customers as well - It's really good stuff but to say it will prevent all cracks!(implied in other posts/threads/elsewhere).