Mold in Nature
First of all, mold is a kind of plant that belongs to the family of fungus. In this family there are mold, mildew, algae, and mushrooms. In nature, mold is beneficial because it works on wood, leaves, and organic matter to digest and convert it to rich soil. But, what is good on the outside is not good inside.
I found this rock in the front yard of the family home that we treated for attic and crawlspace mold. The thing is that mold doesn't grow on rocks. There are types of algae that live on minerals. We see this algae on roofs. But, what is really happening here is the pitted rock is holding a collection of soil and organic matter. So, the mold is feeding on the organic matter held by the rock rather than the rock.
Mold loves cellulose. So, wood is pretty much its favorite meal. It likes paper and cardboard as well.
Like a plants, mold has a root system that digests the wood, and over time makes it go punky, and destroys it. Mold produces mycotoxins to break down the wood; and as you might expect, mycotoxins are bad for our health.
Bleach only kills the tops of the mold, but not the root. There are professional products that will kill the mold.
But, here is the most important issue for homeowners. Mold never gets better, but is working 24/7 to destroy your home. Never allow mold to grow in your house. It will destroy the wood and harm the health of your family.