It might be as its like crusted salt. I have never seen it before and its only down the fascia. No one else in the area has it and I can't work out where it has come from.
What are the roof tiles made of ? If cement I think it could be lime from that run down on the under felt and down the facias . I have had similar on odd occasions and never succeeded in getting it all off just did my best and explained to the customer , I have used a scraper ti get it off but it permanently discoloured the in my case white plastic
I think you are right, I will spray on white vinegar as I have 10 litres of the stuff and leave it for a while. Quite unsightly and couldn't understand how it managed to miss the gutter. One would think neighbours would have the same issue as they all have same tiles.
