Bleach is effective at killing mold on non-porous surfaces such as glass and stainless steel. However, building materials such as sheetrock, wood, and cement are porous, and bleach cannot penetrate to the roots of the fungus. Instead of killing the mold, bleach can stimulate the mold to release spores, which can worsen the problem.
Many clients have reported that mold continues to grow in their A/C vents even after cleaning with bleach or similar chemicals. This is because most cleaners are only effective on non-porous surfaces.
