My dining room has had the fireplace ripped out and it looks to have been reboarded, and from tapping it seems to be brick on the outer sides and hollow to over head height, but boarded up.
I've chipped away at some of the board to see what's underneath and I've attached a picture of the white powdery material a cm down.
Anyone know what this is likely to be? Hopefully nothing dangerous to inhale...
Thanks in advance
