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Written by Robert E. Sheriff, MS, CIH, CSP, President
November 21, 2018
Cleaning Mold-Containing Surfaces
Once a determination is made that a moldy surface can be cleaned instead of removed or demolished, what cleaning agents are effective in removing or killing the mold?
Many factors influence the selection of a cleaning agent, such as:
1) The type of surface to be cleaned. Is it hard such as cement or sheetrock? Soft, such as cloth, fabric or wallpaper? Absorbent and thick such as rugs, carpet, drapes or furniture coverings?
2) The extent of the contamination. Light, barely visible or heavy?
3) The ability of the individual doing the cleaning to use strong or hazardous chemicals.
4) The type of micro-organism involved, particularly if bacteria as well as mold (sewers, etc) may be involved.
The safest approach is to use soap and water. This may be effective in removing visible mold from the surface without damaging it. The City of New York Department of Health has established a guideline for cleaning surfaces of molds and recommends soap and water.
Soap and water will not kill any residual mold or spores left on the clean surface, but it is safe to use and will remove the mold as well as anything known. This is the prudent approach for anyone who is not skilled, trained and properly equipped to use more hazardous materials that can be as dangerous to the applicator as to those little microbes! Thus, if you’re not properly trained and equipped to handle biocidal agents (chemicals that kill microorganisms), stick to soap and water. If a more thorough cleaning effort is desired, you should use a qualified professional who has the licenses, skills, personal protection and training to do a major cleanup..
For hard non-porous surfaces, a bleach solution (Sodium hypochlorite or calcium hypochlorite) can reduce the amount of mold on the surface. However, even using full strength, undiluted bleach is not totally effective at killing mold spores. Only a bleach solution of 10% or greater can effectively kill mold spores. 10% bleach solution is not available to the consumer but must be purchased through an industrial supplier and only used by properly trained, equipped and protected individuals. Of course, these bleach solutions can damage the surface to which they are applied. Ideally, a residual should be left on the surface for some time to be most effective. Thereafter, it often needs to be washed off to prevent surface damage. Again, the need for qualified people.
Chlorine dioxide used as a gas or a liquid is very effective as a biocide. The gas is deadly and must be used in a vacant, sealed location by skilled applicators. Chlorine dioxide as a liquid is effective but must also be used by a skilled applicator. It is effective in killing bacteria as well as mold so it is preferred for floods or sewer backups where both mold and bacteria exist.
Quaternary ammonium salts, generally called “quats”, are also effective against molds. They have been used as disinfectants in food processing for years and are effective against both molds and bacteria. The combination of several different of these ammonium salts is important since each different ammonium salt tends to be effective for a narrow range of microorganisms. Check with the manufacturers and only use skilled equipped individuals.
Some biocidal agents contain alcohols which are effective and often cause less damage to cleaned surfaces. However, they may be combustible, and workers must have suitable respiratory protection and have the knowledge to deal with such chemicals.
Effective cleaning of clothing and fabrics containing mold is difficult. Hot water and soap will remove most molds but may not kill the spores. Dry cleaning is not effective in removing mold or mold spores or killing them either. The most practical approach is repeated washings with water as hot as possible. Add bleach if it won’t ruin the fabric! All which leads to the conclusion that if mold has permeated clothing it may have to be discarded.
In summary, soap and water will clean most surfaces and can be used safely by the consumer and is least damaging to the cleaned surface. Use of bleach, chlorine dioxide, quarterly ammonium salts and certain alcohols can be effective but one must follow the manufacturer’s guidelines and understand the limitations of each agent and its hazards by being properly licensed, trained, equipped (and insured!).
Of course, none of these agents are intended to decontaminate sites suspected of bioterrorism. These situations must be handled by enforcement agencies and decontamination experts.
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