Apartment next door got flooded and some water sipped underneath the wall. The floor buckled and had to be replaced. After removing floor trim I discovered some mold under the baseboard.
I cut out a portion of drywall (see 2nd pic below) and sure enough, there is mold on both sides of both layers of drywall. But the mold formed only on the surface, in the paper coating. The gypsum itself looks white and clean. So here's the dilemma: should I simply scrub and clean with 1:10 bleach solution, or should I cut and replace affected part of the wall? I already made the decision to replace trim boards.
Bonus question: is there something I can do to prevent this from happening again? For example, can I put some kind of water barrier inside the wall, since it is likely that I will have to open it up anyway?