Why Mold Grows

A common question that we are frequently asked is "why can't I just throw some bleach on the mold?" While bleach is a great product when used as it is intended, it has never been intended for mold cleanup, especially on porous surfaces. Bleach manufacturers' labels state the products is effective on "hard, nonporous surfaces". While bleach is effective on tubs, tile, countertops, sinks, toilets, etc, it is not a good choice for use on wood, drywall, carpet, trim, floor joists, attic sheeting, etc. So why is bleach not recommended for porous surface?


  • bleachBleach is unable to cut through dirt. Prior to sanitizing a surface, it must be cleaned. Dirt and mold growth must be physically removed prior to applying an appropriate sanitizer. [In a 2004 study of five different household products to try to clean a moldy shower curtain, The Wall Street Journal reported that the least effective product was chlorine bleach.]

  • Bleach damages floor finishes: Bleach attacks floor coatings, eating away at their appearances.

  • Bleach damages fibers, carpets etc. Moldy carpets and fabrics should be discarded as part of mold remediation.

  • Bleach corrodes hard surfaces: Metals and other surfaces can not only be corroded, but discolored.

  • Bleach can hide dirt: Bleach can make some soil transparent and dirt left behind can still foster mold growth.

  • Bleach loses strength rapidly: Chlorine begins to break down quite quickly and consistently after bleach is manufactured.

  • Chlorine Bleach is NOT a registered EPA mold remediation product. You can verify it yourself when you are unable to find an EPA registration number for mold application on the label of any brand of chlorine bleach.

  • Use of Bleach on porous surfaces can accelerate mold growth. Bleach cannot penetrate into mold's tiny hyphae (roots), but the water part of the bleach formula will. This may allow new growth to occur with the introduction of new moisture. Using bleach on these surfaces can actually spread mold growth.

    What About the Use of Ozone to Decontaminate Moldy Buildings?

    by Dr. Harriet Burge, Director of Aerobiology, EMLab P&K, SanBruno, Calif.

    Most of the studies of ozone are found in the food industry. Ozone is effective in slowing the growth of fungi on fruits and vegetables. While significant in the life of a vegetable, this delay is usless for a residence.

    It is true that very high levels of ozone over serveral hours will significantly lower the concentrations of culturable fungi on hard surfaces. At these concentrations, however, the ozone will damage building contents. Also, ozone disappears rapidly from the air. It attaches onto surfaces (including valuable ones that could be damaged).

    Remember also that dead fungi may cause as many problems as living ones. It is far more effective to not worry about whether or not the fungi are alive, but instead concentrate on fixing the water problem and removing materials with fungal growth.
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