Anyone know what this is (damp/blistering paint?)

[Harlequin565]

Not had this before and it's been there a while but now my SO has decided it needs sorting out. If you pop the blisters, water comes out so I guess it's damp, but I have no idea who to call to get an opinion on a)what's causing it and b)how to fix it.

Plumber? Painter/decorator? Glazier?
All help gratefully appreciated.

 

[kendo1]

Builder.
Probably a gap in the sealant under the window on the outside.
It's a good place to start looking.

 

[broc]

Is that the window cill or one side (i.e. vertical)? I agree with @kendo1 it looks like a gap in the sealant allowing water in, I would check all around as wind & gravity can affect where the water ends up. Sealant goes hard & brittle over the years or it could just be carelessness when the window was installed. Depending upon skill level it could be a cheap DIY job to remove any hard sealant and renew it with a tube of suitable sealant from Screwfix or similar establishment?

 

[Harlequin565]

Is that the window cill or one side

It's the sill.

Thanks guys. At least it's a place to start. I'll have a look outside after work.

 

[arclight]

It's the sill.

Thanks guys. At least it's a place to start. I'll have a look outside after work.

If the painted material is wood it could be worth looking for contamination (fungus) and, if so, get something to kill it to prevent a recurrence.

 

[Sky]

You can also get a similar effect when incompatible paints are mixed . . .