Mold after a storm damage
If you have mold on the walls in your home then it's usually easy to remove. If the wall is non-porous then you can simply wipe the mold away using a wet cloth. You can also use a mold killing product if you like.
However, if the wall is porous, such as unpainted drywall, then you will usually need to cut away the wall where the mold is growing. This is because mold grows inside the material, instead of just on the surface, and so you can't remove it completely.
Mold on Drywall Walls
Because drywall is a substance high in cellulose, it is one of the most common materials mold grows on in the home. As there is no practical way to completely remove mold from drywall, you will have to cut out and dispose of any drywall you discover which has mold growing on it.
Mold Growing Behind Walls
Mold commonly grows out of sight behind walls in the wall cavities. These spaces often contain pockets of humid, moist air. Mold can also grow hidden behind wallpaper. Wallpaper glue can hold organic debris, which can then become a food source for mold growth.
To find hidden mold behind walls you need to use invasive inspection methods and, optionally, mold testing. It's best to talk to a professional mold specialist in this case.