Hello all, i've owned my 3 bed end terrace for 4years and since buying there has always been a large yellow stain on the ceiling of the back bedroom around the chimney. I've recently stripped back the plaster on the ceiling to find some mould like damp around that area on the plasterboard. As someone new to this i could really do with some advice on where to go from here. I will try to add a photo. Thanks for your help