Oh, so your guy said to turn up the A/C?
I'm not aware of anything like this. We have plaster walls here in most places (the tiled walls are mostly in the guest room the bathroom, and the kitchen) and I've never seen any damage attributable to heat or humidity per se. And Bombay, India is both hot and humid. And we're near the sea, too. On the other hand, we have extensive damage attributable to rain - the monsoons here are brutal. But that's not what you're talking about.
ADDENDUM: I should have read the rest of the thread first. Never mind, ignore above comments.