Garage exterior wall does not dry / plaster does not hold

Hello

I have a garage wall where the plaster does not hold. I have already tried several times to smear plaster over it, as can be seen in the photos.

According to the roofer, everything is sealed from above. Could the moisture also come from below? As can be seen in the photos, it is very dry.

How should I proceed?

Thank you

Have already tried several times to smear plaster over it,

Is this supposed to be a joke?
I'm no plasterer, but first the old plaster has to be removed. Then you repair the cracks and disastrous spots (don't know if epoxy resin is also used here), and then you work with reinforcing mesh. And then you don't smear either. Plastering means applying a thin layer.
Another source of error could also be the wrong plaster.