Hi, My partner and I are new house owners and slowly learning so many new skills! Was wondering if anyone could help with a patch of blown plaster, see photo. We recently noticed this patch at the back corner of the house. There’s a roof right above this and the gutter is on the exterior corner of where the damp patch is so we think there’s a leak of some kind which is why it’s been caused. Roof guy is coming tomorrow to look at the cause but wondering on any tips to solve the blown plaster? Do we need to test the rest of the wall and how do we do this? How do we know it hasn’t spread? Do we need to get someone in to fix it or could we do it ourselves? And any tips to make sure it doesn’t come back! Any help would be greatly appreciated.