Need advice please - tiling "poor" ground floor concrete floor

[Old_Brown]

Any advice gratefully received on tiling a concrete screed that is according to the builder not in great condition. It had a ridge down the middle from a wall (originally two rooms) and distinct areas where there had been a toilet pan and soil pipe. So the builder has hacked off the ridge and laid self-leveller to the floor. It now look OK to me, but he said it's not got a great DPM and is not very thick screed over the sub base. So he was talking about a decoupling layer.

We also have the decision of electric UFH as well.

I've considered a brush on black DPM under a board like No-More-Ply. Other suggestions are to use Marmox Board or Ditra.

There is 35 mm max under in inward opening patio door.

Any advice gratefully received.

 

[Andy Allen]

Is the builder going to be doing the tiling?

 

[White Room]

You will need a thermal board under the ufh....

 

[TJ Smiler]

What does the builder mean by bad condition?

 

[Old_Brown]

Is the builder going to be doing the tiling?

Afraid not - that would be too easy - it's going to be me - the money for builders has run out.

I've tiled a few "good" areas and new areas, with no real trouble.

 

[Old_Brown]

What does the builder mean by bad condition?

Thin screed over an uncertain base.

 

[TJ Smiler]

How thin? I argued this with a builder for the whole of last week. His screed was 15mm thick and mixed ratio 4;1, i told him it was to thin and it wont hold, he told me he has done loads of screeds that depth and have all been fine.................. By the time we stopped arguing at the end of the week the screed had failed and i was enjoying his failure and enjoying telling him what a plank he is.

If the screed is thin (say less than 50mm then i would take it up and latex it with a fibre reinforced SLC.