Hi... a bedroom wall (first floor) suffers from several small patches of efflorescence, scattered around on the inside. Two years ago I stripped back the damaged areas, allowed them to dry and re-sealed the wall with a damp wall treatment. I then re-decorated. But it came back. Earlier this year I stripped the patches back again and left them to dry out. I also painted the outside of the wall, assuming the damp was penetrating from there. For two months there was no efflorescence. Hoping the problem was solved, I have re-decorated again. But within a couple of days, it's back! The paint is "bubbling" up in places and is "crunchy" to touch. It obviously hasn't rained and I can see absolutely no evidence of a leak... so where's it coming from? And what do I do next?!