Any ideas or advice

Brimstone

Well-Known Member
Common problem, looks like rising damp, older properties didn't have DPM under the back hearth slab. Fires used to keep it dry/down. Have to sort it out from the electric fire side - new conc back hearth with DPM/DPC underneath.
In theory it might be roof flashing failure but that usually shows in the walls not on the ground.
 
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