When 2" or 3" wide gap between fire door frame and precast concrete wall happens, how can I fill up this gap?
I heard 2 or 3 hour fire-rated door needs special treatment.
You wouldn't normally expect a 2 to 3" gap at that location... maybe 1/2". For a 2 or 3" gap, I'd expect some firestopping and maybe some intumescent caulk. Possibly a bent metal channel... part of a firerated assembly.