Doing 3 rooms in apartment block, all have carpet on lino tiles on bitumen on concrete.
Planned to remove as much bitumen as poss using heat gun + scraper, sugar soap clean then slurry coat 50/50 SBR/rapidset flex (mapei/tile giant proflexible).
Problem is 2 rooms have a 180mm strip of ply which is well screwed down, no flex separating concrete. This obviously runs across the whole apartment.
In 4m x 2m kitchen the strip runs across the 2m width about the middle.
In one bathroom it's about 70mm into room.
Laying full bodied porcelain tiles no ufh. Do I need decoupling membrane or would keraquick with latexplus do the job??

Anyone have opinions on this please friends?
Thanks....

The only thing I can think of with the ply it has pipes running underneath for access

Originally Posted by whitebeam

The only thing I can think of with the ply it has pipes running underneath for access

Correct mate, on further investigation 25mm ply covering pipe channel in concrete. So on the upside it's the same slab of concrete but how will heat from pipes affect things assuming happy with deflection factor..........?

Really you should have expansion joint in the tiles at every joint between ply and the screed even if it is deflection free but of course that would look awful. Hmmm... Have you had the ply up? Any chance of filling the channels in? It wouldn't be ideal but I would feel better tiling over a channel that had been filled in rather than a hollow channel covered in ply.

it's 25mm thick over only 180mm wide and well screwed down so deflection not an issue. What are the issues here, expansion/contraction of ply absorbing heat from pipes? Would decoupling membrane not absorb that?

Just uncouple it and it will be fine, stick down with keraquick and latex plus


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