New screed meets old - decoupling membrane?

[MattChan]

Hi, I had a small kitchen extension built a couple of years ago. The new sand and cement screed has been taken right up to the old one over where the old external wall used to be. Obviously after a couple of years this has now well dried out and is crack free. The new floor has more insulation than the old, neither have UFH.

The area is a lower case d shape with 2.4 x 2.4m to be tiled in the old area and 1.2 x 2.1 to be tiled in the new area.

Whats the best solution here, cover the screed in a decoupling membrane and tile on? Just put an expansion joint at the join in the screed to allow for any differential expansion? Just tile straight on with no special precautions?

 

[robinbanks]

Dare say if it was going to crack it would have already, but if you don't way to lay out for a DCM and are in any way concerned that the joint in the screeds would crack, lay the tiles out so a grout line is along the joint. Difficult to see where this differential movement would come from btw..