I live in an apartment in a multistoried building. The building is assembled of huge enforced concrete plates - one plate is size of a wall of a room. One of the inter-plate seams has a crack in it due to a slight basement slump (the code allows that) that lets the cold from the outside (the atmosphere) into the apartment.
I need to choose some compound to seal the seam from the inside of the apartment. The crack is about two millimeters wide and I could use ordinary cement-based mortar, but the problem I see is mortar is not elastic, so if the building continues to slump the crack will surely reappear and I'll have to start anew.
I could use silicone-based sealant, but it is not fireproof and I don't like the idea of a fire suddenly bursting from inside a wall if there's a fire in some other apartment.
So I'd like to have something like a cement-based mortar (fireproof) yet flexible enough to compensate fro future slumps. Are there such compounds?