The active ingredient in bleach does not penetrate porous surfaces. So you wind up adding to the molds moisture source allowing the hyphae (mold roots) to grow more Bleach is very good at removing color from mold, giving you a false sense of successful mold removal Bleach is very corrosive to materials and hazardous to your health OSHA and the EPA recommend bleach NOT be used for mold remediation There are many alternative anti-microbial solution options readily available that do a better job and are less harmful.