I've been told that a plastic sheet can actually cause more of a problem by trappin moisture rather than breathing... so hard ot know what to do and so frustrating that the guy didn't use the right amount of the DPM - we'd have never had had this problem!
Part of our house is 1950s blockwork without DPC or proper DPM in the kitchen area.
After a botched job to put in a liquid DPM (so we can have laminate) this is what we've been left with from top down:
5. Top layer of Ardex NA. This layer has cracked in places (10 days after works were complete)...