Is coating slurry possible on paint? Or are there alternatives?

Hello,

we have moisture in an apartment that comes from the outside of the building. The neighboring building was demolished and the exterior wall is now exposed to the weather. We will also carry out work on the exterior wall. However, before that, we wanted to work with sealing slurry on the interior, then insulate with Styrodur, and afterward install a drywall.

Now I have read that sealing slurry cannot be applied to a wall with paint on it. Is that true, and if so, what would be the alternative? And what do you think of the Styrodur insulation on the interior? Unfortunately, the wall is far too cold and does not really warm up in winter.

Thank you very much in advance.

Best regards

If the dew point cannot be calculated exactly, for example due to material issues, one might perhaps consider having it calculated. According to my rough estimate, it would most likely be at a point where one does not want it. That does not sound good to me. Best regards Gabriele