Should I Spray Bleach on my Mold Growth?

The presence of active mold growth inside an occupied building requires remediation measures to remove the growth. Existing industry standards published by the Environmental Protection Agency (EPA), American Industrial Association (AIHA), Institute of Inspection, Cleaning and Restoration Certification (IICRC), American Conference of Industrial Hygiene (ACGIH) and others all emphasize  the need to remove the mold growth. This is defined as the demolition and removal of affected porous materials such as carpet, drywall and insulation, and the thorough cleaning of non-porous materials such as wood, metal, vinyl and hard plastic.

The reasoning behind this advice involves the allergic nature of the mold organisms. We do not know precisely which part of the organism causes symptoms.  Is it the living organism, its vegetative parts (the furry growth you can see on the wall), the spores and spore forming structures, volatile organic compounds, mycotoxins or something else?  Since it is unclear, the advice is to remove the whole kit and caboodle.  Then there is no doubt.

So the approach of spraying a biocide such as bleach on the growth violates this fundamental premise. Even if the biocide actually killed the mold (unlikely as explained below), the dead organisms, spores and mycotoxins are left behind.  These parts are just as allergenic as the living organisms.  You really have not accomplished much by simple spraying.

First, one must remember that caution is advised in the use of biocides, to ensure that we humans are not exposed to chemicals that can be hazardous with uncontrolled use. These products are designed to kill organisms and are generally hazardous to humans.  There is no point in replacing a biological hazard with a chemical hazard.

Additionally, the biocides may not even put a dent in the mold population. Most of the biocides are oxidizers that react with any organic material.  Organic materials include wood, paper and the dust and dirt that just seem to hang around.  Once the oxidizer reacts with the organic matter, it is no longer available for the mold colony.  You will find that more often than not, the mold returns after spraying because it has not been eradicated.

And what is left over after the biocide ingredient is used up? Water!  Virtually all biocides on the market are aqueous, comprised primarily of water.   Consider the case of chlorine bleach.  The stuff in the bottle that you buy is 3% hypochlorite and 97% water.  But you don’t use it full strength, you normally make a 10% dilution, which means the bleach that you use is 0.3% bleach and 99.7% water.  Spraying bleach on mold is equivalent to spraying gasoline on a fire.  You are giving the mold more of the moist environment that caused the problem in the first place.

So when it comes time to deal with mold, remember the words remove for porous materials and clean for non-porous materials.  Use a good cleaner, such as Murphy’s Oil Soap for finished furniture, Mr. Clean Power for dirty surfaces, and Formula 409 for surfaces that need to be sanitary.  Think of what you would use to make your car shiny clean, which is old fashioned soap and water combined with elbow grease.  If you use bleach on your car, we need to talk.