Whilst insulating the loft of our Victorian mid terraced house we noticed patches of lumpy white deposit on brickwork and mortar of the chimney breast which looks like lumpy cotton wool. It is soft and turns to powder when you touch it. Worried incase it could be dry rot we have scoured the net for pictures and they dont match (thankfully!), nor is there any evidence of the deposit on any of the nearby timbers.
At first we thought someone had been trying to patch up the old lime mortar with that polystyrene filler stuff you get in tubes but when we touched it, it was soft and came off easily tuning to powder in our fingers.
Any ideas about what this might be and if we need to do anything about it please?