Outside wall of a bedroom has suddenly got wet patches.There are 8 or

Chris Plastow

This can be one of two things , in most cases. 1) old chimney bricks causing hygroscopic dampness 2) poor plaster repairs to wall causing hygroscopic dampness Try to scratch a piece of plaster from +- the middle of a damp patch, down to the render. Measure the thickness of the plaster. If it is more than 2mm, that is the problem most often