Hi, I have a gap that is 1.5 - 2 inches from the window frame to the brickwork and goes a few inches where the plaster was loose and cracking (presumably because it wasn’t attached to anything). Is the best option to just use mortar to fill in so it’s flush with the brickwork? Should I mortar behind the frame up to the stud behind it or is there another step I should take to prevent moisture or other issues?
Many thanks