I only have glass tanks with screen lids. If you have a water dish with a large surface area (perhaps over an uth or under a heat lamp) and keep a large portion of the lid covered with plastic, it should be fine.

For my 40 g tank I have a piece of cardboard cut to fit about 2/3 of the lid, and that's inside of a garbage bag taped to fit.... It's just cardboard wrapped in thin plastic.. Easier to remove than say taping a piece of plastic down over the top. It traps the humidity pretty well, and I just mist the inside a little with a spray bottle here and there.

As for the quickcrete I have no idea what that is or what you're talking about lol. But I think putting concrete or anything similar in the tank sounds like a bad idea to me. I don't know though. If it's heavy it might break the glass on the bottom?