If this has just appeared its more likely to be penetrating damp, due to a problem with your outside stone work ,pointing, rendering.Or if you have changed your levels outside as in your flagging or tarmacing in the back garden it may well be rising damp. So have a good look at the fabric of the building outside around the site of the damp and also take a good look at the window itself.Hope this helps
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A true man of character knows his limitations – but doesn’t accept them.
Aggressive by Nature, Rugby by Choice
