On 17/07/2019 16:48, R D S wrote:
On 17/07/2019 15:40, newshound wrote:
Perhaps, or common or garden rising damp but held back by an
impervious plaster, or plaster over tanked brickwork?

Has rising damp not been debunked?

Everything credible that I read suggests that 'damp' comes from above
somehow.

Not true.