ᐅ Damp or Moisture on Interior Wall After Completion of Exterior Stucco/Plaster

Hello dear experts,

I am a bit puzzled. About two weeks ago, the exterior plaster on our new build was completed (mineral-based plaster).

Now I have noticed that the wallpaper on one wall in the living room has started to peel off. I removed the strip, and underneath it is damp in some areas. My measuring device shows values up to 120 digits. There are no water pipes or anything similar in this wall. I have now created a measurement grid; towards the window it is dry, but the moisture seems to be rising from the bottom in the middle of the wall. However, above a height of 1.50 meters (5 feet), everything is dry again. The wall is between two windows and about 1.5 meters (5 feet) wide. The masonry is pumice blocks filled with perlite.

It hasn’t rained for days. Where could this moisture be coming from? Could it still be residual moisture from the plaster?

Best regards
Basti, the desperate homeowner

Underfloor heating leaking?

The joints of the floor and base tiles are dry, the system pressure is stable, so I think we can rule that out.

What’s strange is that the moisture level in zone 1m is the highest (120), while in the base area it is around 70.

Maybe you should provide a few more details. Which utilities are nearby (floor plan)? How long was the interior plaster allowed to dry?