ᐅ Smoothing and Painting Concrete Ceilings in Outdoor Areas

Hello everyone,

Our precast concrete slab is used as a roof covering for the terrace outdoors. I would like to fill the joints and then paint the entire ceiling. Indoors, this was done with a gypsum-based filler and joint compound. However, at least the gypsum filler is only approved for interior use.

Which materials are best to use here for outdoor conditions? What type of paint would be suitable, exterior paint?

Definitely use facade paint.
For filler/plaster, the specialists here can provide more information.
This only concerns the lower ceiling, right? On top of that, there will surely be a bitumen membrane and so on...

Yes, only at the bottom. On top is the balcony with a flat roof membrane as waterproofing.

Ardex B10, suitable for rough Ardex B12; approved for both interior and exterior use

Actually, any other concrete filler should work, right? Can I sand it with a regular drywall sander?

None come to mind immediately that are not rated for outdoor use; just check the datasheet. Giraffe works.