Extend half wall 20-22mm

[Pellepax]

I will try to get a flat wall in the bedroom after an interior wall has been removed and half of the garage has been turned into living space. There is now an edge on the exterior wall where there is a difference of about 22 mm between the exterior wall in the old garage section (built in aerated concrete) and the old living space (wooden frame). Today, there is gypsum on the wall in the old living area while the aerated concrete has nothing on the outside.

Should I just put OSB (or ply) 15 mm and then a 6mm renovation gypsum on top of the existing gypsum, or should I first tear off the existing gypsum? There is some type of rough-boarded panel behind the gypsum on the wall now.

 

[August.E]

I will try to get a flat wall in the bedroom after an interior wall has been removed and half of the garage has been turned into living space. There is now an edge on the exterior wall where there is a difference of about 22 mm between the exterior wall in the old garage section (built in lightweight concrete) and the old living area (timber frame). Today, there is plaster on the wall in the old living area while the lightweight concrete has nothing over it.

Is it just a matter of putting OSB (or ply) 15 mm and then a 6mm renovation plasterboard on top of the existing plaster, or should I first remove the existing plaster? There is some type of rough sawn panel behind the plaster on the wall now

I would go with 10mm OSB/chipboard + 13mm plasterboard. Considerably cheaper than 15mm OSB plus renovation plasterboard, which is both expensive and fragile.