Damp meter

[JoeyB]

I had a new chemical damp course installed.The wall was replastered etc.I put polystyrene sheet on the wall in two outside walls and then lining wallpapered over.The paper looks yellow in places and the meter indicates moisture .There is no indication on the unlined walls.Could the polystyrene be causing the problem.

[Ethel]

How long ago was the plastering done?

Plaster can take an age to dry out fully and if the polystyrene was put on while it was even slightly damp it will only get worse.