Brown stains coming through wallpaper

[alarman]

Hi All
There are brown stains coming through wallpaper in bedroom, its on exterior wall and slightly on internal. Checked pointing outside and looks quite sound, wall doesn't feel damp, so not sure what is causing the problem. Any ideas please

 

[joe-90]

It's probably condensation making the wall slightly damp and then you get that brown staining. When it appears on book pages it's called 'foxing', but wallpaper is just as prone.

 

[alarman]

Thx. So if i strip what preperation do i need to do?

 

[joe-90]

E$ither improve your ventilation or put that insulating type of lining paper up first.

 

[alarman]

Thx. Would it be worth painting with zinzer damp block or is that going over the top?

 

[joe-90]

It won't help as the moisture is in the room and condensing on the walls - like breathing on a window.