Damp/wet patch under the bay window sill 1930's house????

[actiongirl5]

We recently bought a 1930's house with a bay window in the living room. Whilst removing the wallpaper under the window we found black mould which was exacerbated by the wall being covered in polystyrene sheeting. The wall under the bay window had dried out nicely and we then had the plastered knocked back to the brickwork and replastered.

Over the last week ago we have experienced some snow and rain and have noticed a damp patch appearing in the right hand corner directly under the window sill and it radiates outwards from this point. We have ruled out rising damp, as the floorboards, skirting boarding and wall are sound. Even when it was riddled with mould the plaster had not blown out. We have looked outside of the property to find a cause but we are really struggling to find something that really stands out.

The bay window is a uPVC window with a stone sill on the outside, it has no cavity wall and is stone faced. The external brickwork looks alittle mossy near the ground and some of the stone bricks feel alittle sandy on the exterior but nothing that really scares you too much.

Does anyone have any ideas/information/solutions to this problem. All help will be gratefully received.

 

[foxhole]

Rain penetrating around or thru frame needs resealing.