The ceiling on the portico in front of our house was replaced a few years ago. When it was replaced the new ceiling looked terrific and we were delighted with the result. Move on a couple of years and a few heavy rainstorms over time and the ceiling was beginning to look a bit suspect.
I thought the stain looked similar to mould so decided to give it a go with some bathroom mould remover spray. I got out the ladder and set to work. Sure enough after leaving the spray on for ten minutes I then wiped it off and the ceiling was back as good as new.