We recently had to get some repair work done to the rear wall of our house. As part of that process a trellis was removed, which uncovered a stained section under a central heating overflow. What's the best way to clean this, also it's right next to the reinforcement patch, which had only just been completed? Update: I can't seem to let you guys/ gals see the photo I took, as the image icon wants a URL and I chose my Dropbox account to store it. So, apologies for all the icons - which I can't get access to for deletion!