This home is from late 70’s early 80’s. White residue all over walls in living room and downstairs hallway.
A restoration company cleaned up a flood in the home last year. Three months ago white residue started showing up.
Moisture levels extremely low (<10% in all drywall throughout the home).
Furnace filter dirty with white material.
Suspect drywall/construction dust however the restoration company came back and say I am crazy and drywall dust is less “gritty” than this stuff.
Have collected samples and processing this week.