ᐅ Plastering the interior surface of a roller shutter box with lime-cement plaster

Hello,

we received our windows with recessed roller shutter boxes.

The polystyrene insulation is not completely flush with the masonry; it is set back by about 15 mm (0.6 inches) in some areas.

The construction company suggests installing rigid foam boards (extruded polystyrene), while the window supplier says that the roller shutters can be plastered directly (at the time, I didn’t realize they were not flush with the masonry). Now I wanted to get the plasterer’s contact, but I’m not sure if I can reach them in time.

What do you think? Should I install rigid foam boards? And how thick can the lime-cement plaster be?

That’s not a problem at all. It can simply be skim coated. Up to 2cm (1 inch) in a single layer should be doable; otherwise, multiple layers will be necessary.

I would level everything with Styrodur and then apply a contact layer using adhesive reinforcement mortar.

Please ensure that the box can be opened later with minimal damage. At some point, it will need to be opened.