We had another guy out today and he said similar, but believes the damp course is worn out and needs replacing. Upstairs and top half of the downstairs walls are bone dry so I guess rising damp is the answer.

When you say high ground levels, I may be sounding dumb here...but we live on a hill, is that what you were referring to?

Interestingly too, our garden is slightly uphill so rain rolls down towards the house, not sure if that could be a problem but I'd hope what that was taken into consideration when the house was built...it is a 1960s ex council house (I'm in England), I believe they were built well 🤞🏻

I believe it was there when we moved in early 2020. There was always a strange smell in the kitchen cupboards next to the wall where the chimney is and I just assumed the previous owners kept herbs, onions or something in there. There was never anything visible or obvious until we noticed white mold forming on a pan we never used in the cupboard. Assumed we didn't dry it properly, washed it, put it away and noticed the same thing some time after (few months ago). That prompted me to do some investigating. I pulled back some wallpaper in the living room where the chimney breast is and the paste was sticky so I knew something was going on. There was no mold that I could see in the living room, no dampness of the wallpaper, only the sticky paste and dark plaster behind it.

This all led to the chimney work 6 weeks ago. I don't know how long it should take to dry out, or if there is more going on. All I do know is that I'm worried all the time about my little boy.