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Stuart Noble wrote:
wrote:
Ed_Zep wrote:
wrote:
Stuart Noble wrote:

It's a tough one this, but you can probably achieve more by observation
and a bit of logic than some builder coming in cold and hazarding a
guess. The fact that it's an internal wall rules out a lot of the
potential causes

yes, leaving only 2 likely options.

Leaking pipe or real rising damp?

leaking pipe or condensation, rising damp is highly unlikely.

Condensation in a heat wave?

yes. I suppose you want an explanation. It is temp difference that
causes condensation, not absolute temp (assuming we're talking above
freezing). On a hot day the air can hold a lot of water vapour (the
hotter the air, the more water vapour it can carry). If the hot air has
highish RH, and meets a cold wall on wet ground, the 20C drop can cause
condensation. Although summer condensation is less common than in
winter, it does occur.

NT