ᐅ Slim slab or exposed concrete

For fire safety reasons, the joints need to be sealed.

Besides, the appearance is not great right now – concrete tends to run down there occasionally.

Even without fire protection (is that really safe in a private single-family home... No one ever mentioned this to us), the joints are quite unattractive. At least in our case, it wasn’t a 2mm (0.08 inch) joint, but due to the beveling at the edges, it was about a 4cm (1.6 inch) joint that tapers toward the top, with quite a lot of rough concrete residue inside. I find it hard to imagine how this can look neat without filling. And since it’s almost impossible to match the original color and texture, painting, wallpapering, or something similar will be necessary afterward.