Damp on wall behind rad.

[mickespite]

Please see the pics below.
I've spotted some damp on this outside facing wall (first floor) and not sure how long its been there.
My first thoughts are maybe there's a leak in the radiator pipe behind the plasterboard.
The leftside of the rad is easily explained by the bath but the right side of the rad has me puzzled.
Any ideas ?

 

[mickespite]

[TonyT]

Salts coming out of stone/brickwork?

[mickespite]

No , I don't see any salts.

What would the presence of them tell me ?

 

[TonyT]

Wall drying out, paint preventing wall breathing so plaint blistering 

[Dave Jones]

wall makeup ? Insulation ?

 

Rad heats wall. outside gets cold. Dew point is close to inside surface. Dew forms when rad cools down. Just a guess.

 

More insulation to cure.

[mickespite]

47 minutes ago, Dave Jones said:

wall makeup ? Insulation ?

 

Rad heats wall. outside gets cold. Dew point is close to inside surface. Dew forms when rad cools down. Just a guess.

 

More insulation to cure.

How could I get more insulation in there though. Its a cavity wall, building built in the early 2000's i believe.