Damp in bedroom

[kaneda*w]

Hi, we've had damp problems in a unused upstairs bedroom for a few years now ,there was so much moisture in the walls that it caused a electrical socket in the wall to blow a fuse , we've since had that socket removed and rewired the electrics in the room, now we want to replaster and paint the room but whats best way to deal with the damp first? , it's rendered on the outside and I've noticed there are cracklines in the render that could be letting rain soak through.
A plasterer I spoke to over the phone has told me it can also be repaired from the inside without having to fix the exterior render? some sort of waterproof layer?

http://img.photobucket.com/albums/v166/midnight*racer/002_zps771ad334.jpg

 

[skhudy]

Are you sure it's not a leak from the roof? Loose tiles / blocked broken gutter running water down the wall? That's too much to be soaking through hairline cracks I'd have thought. You need to sort out the source of the water, hiding the problem inside will build up problems for later.

 

[kaneda*w]

Are you sure it's not a leak from the roof? Loose tiles / blocked broken gutter running water down the wall? That's too much to be soaking through hairline cracks I'd have thought. You need to sort out the source of the water, hiding the problem inside will build up problems for later.

yes in the past there has been loose tiles cause by strong winds which have let in rain , there's no problems with the roof at the moment but I cant tell whether rain is still getting in from somewhere because the staining you see in the pic has been there for a while now , I suppose I could give the wall a quick coat of paint then wait and see if any new damp/stain patches appear?.
ideally I want to find a quicker solution .

 

[skhudy]

Your first post mentioned a damp problem and your last post says is staining. You need to clarify which it is and an experienced plasterer can advise.. painting over a previously damp wall I don't think will tell, the staining will still show through. Damp meter I think is the best way, start around about £15