Strange brick?

[Skiathos]

Renovating a 1950s apartment and came across this. I would like to keep the red brick but there seem to be some gray stones/blocks with a strange shape. I have tested drilling and the drill does not turn red. I don't want to tear down too much because if it's not "rötegel" all the way, we were thinking of plastering over everything so it becomes a concrete wall. There shouldn't be any overhead cabinets on this part of the kitchen

 

[surris]

Lightweight concrete

 

[Skiathos]

Lightweight concrete

But it's such a strange shape

 

[Demmpa]

The red brick is probably fireproof brick, probably only where the chimney is.

 

[Skiathos]

But what is that gray thing in the middle then

 

[jonaserik]

As they say, 2 stripes can be seen from the ceiling down, a crooked duct, behind there is probably the smoke channel and the rest of the masonry is brick, what is on the floor below, maybe a boiler room with a boiler that is gone

 

[Skiathos]

Apartment below, this is on the 4th floor

 

[jonaserik]

Ventilation ducts back then, in the old days there was a vent duct from each kitchen up to the roof, aren't there more ventilation systems going through your apartment, was it the same with other vents too, such as the bathroom

 

[Fotografen]

The gray stripes in the red brick are chiseled-out channels for wiring that have then been filled with mortar.
If you want a nice red brick wall, you will need to build up a thin brick in front, if the floor structure supports it?

 

[Fotografen]

Then there is the chimney in clay brick, and built in with some kind of lightweight clinker where it's "just" wall. Why there is then a splash of brick to the left, who knows? You use what you have, rebuilt sometime before in history?