Mold that grows on porous surfaces can be very persistent and difficult to remove because mold spores penetrate the pores of these surfaces and hang fiercely. In fact, you're probably breathing it right now. And there's practically nothing you can do to get rid of it. This method works because it addresses visible mold, as well as underlying roots that often go untreated.
Surprisingly, vinegar and hydrogen peroxide are more effective at killing mold roots than bleach. Because they work best on different types of mold, try using them together to cover all the possible varieties of mold that you may be dealing with.