Removing The Mold
In a situation like this one, it is often necessary to remove a portion of the drywall to deal with any moisture and wet material that may be causing a mold problem.
Where there is mold there is moisture. That is why it is necessary to take these steps in order to make sure that the mold problem is really taken care of. We often use drying equipment such as dehumidifiers, air movers, and HEPA filtered air scrubbers to help remove the moisture from the environment.
Only once the moisture has been dealt with can you be sure the mold problem has been alleviated.