ᐅ Plastering a garage ceiling with Heraklit not possible according to the plasterer?

Hello everyone,

we are renovating our garage.

The walls were stripped of old, loose plaster and replastered using reinforcing mesh and lime-cement plaster. A finishing coat will follow.

However, my plasterer is having difficulties plastering the ceiling. It consists of Heraklit boards, which were previously skim-coated. The ceiling was also cleared of loose filler, and now the new plaster is supposed to be applied. The plasterer initially said: No problem to plaster, you don’t need to prime, no issue. Now he says the entire ceiling needs to be removed because the plaster does not stick.

My questions:

• Heraklit boards are suitable as a plaster base, aren’t they?

The boards got wet several years ago due to a leaking roof. However, everything has since dried out and the roof has been resealed.

• Is it possible to prime or pre-spray the boards so they can be plastered?
• An alternative would probably be to cover the ceiling again with something like Styrodur insulation boards?

It appears that the boards are glued in place (probably with mortar – I can’t find any nails or screws), and they are very difficult, labor-intensive, and probably not completely removable. Therefore, I would like to avoid the effort of removal.

Thanks in advance!

The topic can be closed; I ultimately removed the Heraklith boards with a great deal of effort.