Scrape off old EPS facade insulation

I don’t know what the glue is made of, but it will be cement with a lot of chemicals. In my opinion, it is too uneven to just loosely put something on it. I would make it even with a thin layer of plaster or glue something on again.

Hm, on the entire facade area of 150m2? I would have to spray the plaster, and a lot of it, even with a 5 mm leveling layer. Is it worth it?

One should also be able to sharpen that. But it is certainly also a lot of work

How thick should the new insulation layer be? A 6cm insulation layer reduced by 2cm has a greater impact than 16cm reduced by exactly those 2cm. Play around with the U-value calculator.

So the insulation is 2 x 10 cm. The glue residue is max 3-5 mm thick. If this does not create a chimney effect, it can hopefully be neglected. The joints between the bricks are also not even as such.

So a total of 20cm? Then I wouldn't worry. Ventilation would of course be the cardinal mistake. Are you actually doing anything regarding airtightness as part of the work? The plaster will no longer provide this.