@Therrion I don't think the concrete is your issue. Rainy weather should not affect your sealed room "in theory" but as Yogi Berra famously said, in practice things can be different.
Rather than hunt for holes in your sealed room, I think your RH issue is coming from having a bumper crop with lots of transpiration. Compounding the problem is your desire to lower temps AND reduce RH at the same time; these are conflicting goals, since RH falls as temperature rises.
What I think you need to do is add heat in your room, as in some kind of heat source. The issue might not be wet concrete so much as cool temperatures sucking extra heat out of the room, which would interfere with the operation of your dehueys.
These are just educated guesses based on what I saw of your grow in your other thread.
The more you can tell me, the more I might be able to help?