Damp and mould front bay window

Damp/mould have appeared on upstairs front bay bedroom. This part of the bay is not brickwork so not sure what type of material was used. We recently treated this area with damp/mould paint. House was built circa 1932. Sometimes there is no damp in this area but sometimes it appears so it is intermittent. Exterior of house was painted roughly 11 years ago. From the exterior side it looks as if it needs to be rendered/plastered/painted. Also the pebble dashing on the opposite side front wall is starting to come off at ground floor level. So, would we be looking at a plasterer/renderer? Also the pebble dashing would need to be redone and we would be looking to have all of the front area redone again. Thank you.