damp plaster

[nkosi bob]

i have had a small leak on my chimney which i have had repaired, I had to cut a hole in the ceiling (dormer bedroom) to view where the leak was, anyway i find that the plaster on the bedroom wall just won't dry out, i have had a heater on it for days and days---- and a dehumidifier for over a week. After heating, the wall it becomes bone dry, but give it a few hours and my meter is in the red again-----the actual brick stack which i can access through the ceiling is bone dry----yet the wall below is damp!!---- the plaster will just not dry out ??
Also, I think the leak has been there for a long while

 

[^woody^]

You can't rely on a meter to tell you if plaster is dry.

Does it look wet or not? If you have stopped the leak, removed damp insulation above, then it will dry out but - depending on the extent of the leak, it can take several weeks