DIY DONNY

WE put a wet wall in our en suite two years ago. I have recently noticed it’s become discoloured in the area where shower water hits it. Can we coat it with anything? will wear it off. Leave the slate to naturally weather. It will go a light grey/matt with a hint of silver. MY son’s bedroom has two outside walls which don’t get a lot of sun. About a quarter of the way up where these walls meet, the wallpaper can be wet, but there is no dampness beneath. The double glazed window gets covered in condensation. What is causing this?