I had part of a 9" wall knocked down for a doorway. Slightly below floor level are two layers of polythene membrane with a layer of floor levelling screed to make up to floor level. I would say the screed was
5-10mm thick.As I had anticipated, the floor has cracked, presumably from voids in the polythene which never laid perfectly flat before the thin screen was put on top.
I was thinking of removing the screed and removing all but 1" or so of the polythene and painting liquid DPM above and below the membrane before applying new screed.
Is that the right approach? What liquid DPM would anyone recommend?