ᐅ Bubbles Forming While Applying Filler over Woodchip Wallpaper – Causes and Solutions?

Hello dear community!

I have started renovating my apartment and have already encountered some problems in the first room. (I don’t want to have the apartment renovated by someone else because I enjoy working myself and like to learn new skills.)

The entire apartment was covered with textured wallpaper and painted over several times, sometimes with latex paint.

The room I am currently working on is now completely stripped of wallpaper. Under the wallpaper, the walls were plastered over smooth concrete (I think it is lime plaster). The next layer was a latex or rubber-like coating (possibly a primer?). The ceiling was not plastered.

I primed the walls with a deep primer and the ceiling with an adhesion primer.

I am using Fill&Finish Light from Knauf (recommended to me as a beginner).

I embedded a type of mesh tape in the corners.

Now, when applying a full-surface plaster for the first time, I notice that bubbles have formed over almost the entire plastered area. They can be easily pressed in and have hollow spaces underneath. The application thickness is no more than 1.5mm (0.06 inches).

Could this be caused by perforating the wallpaper? (I pressed quite hard so that the holes are also visible in the old plaster.)

What can I do about this? I have read that a primer/sealer might solve the problem.

Best regards