Ask an Expert: Remediating Mold

Ask an Expert is an occasional feature where we pose a question submitted by a readers to our Healthy Home Director Carl Grimes and Healthy Building Scientist Joe Medosch.

Reader Question: Can the mold and water damage in my home be remediated safely and correctly by just spraying chemicals?

This is a common question and the short answer is no. Mold removal methods must be effective at removing the mold, safe for the occupants of the house, and not cause unintended consequences later. Chemical sprays and other mold treatments do not meet these criteria.

While the execution can be complicated, the basics of mold remediation are quite simple and must be done in this order:

  1. Completely stop the moisture that is causing the mold to grow.
  2. Contain and physically remove the mold either by cleaning or removal/replacement of the affected surface as outlined in the scope of work by a certified professional.
  3. Confirm the work was fully completed with an independent assessment and/or testing.

These steps should be outlined by a professional, certified as a mold assessor or in mold removal, and are based on the ANSI IICRC S500 Professional Standard for Water Damage and the ANSI IICRC S520 Professional Standard for Mold Remediation. ANSI (American National Standards Institute) recommendations are based on solid, well-documented science and represent the closest thing to a federal standard in existence. In most states, mold remediators have no oversight and are not required to follow ANSI or any other standards. If you are hiring someone to do mold remediation, we strongly recommend finding someone who is certified and will provide a written guarantee that the ANSI 500/520 standard will be followed.

Several key points of the ANSI Standards are especially critical for consumers to understand:

You may notice or be told that chemical spray being used is “EPA Registered”.  It is important for consumers to understand, that while all products affecting micro-organisims, including mold, are required by federal law to have a registration number and approved label from the EPA, this does not mean that the EPA or any organization has independently validated product claims or safety. It just means that the products have ingredients that could be hazardous or harmful, so they are legally required to be registered. Many of these chemicals are not tested for health effects on humans.

Lastly, we want to address the use of bleach on mold. Using bleach on visible mold growth is not recommended by either the EPA or the CDC and is not part of the ANSI-IICRC S520 Standard for Professional Mold Remediation. First, bleach is a chemical and can impact people with chemical sensitivities especially if used in areas that are not well ventilated. Second, on non-porous surfaces such as tile, bleach is no more effective at removing mold than a damp cloth and a mild detergent, so we recommend the least toxic option. Also, since bleach is mostly water, on porous surfaces, such as wood or drywall, the water in the bleach is easily absorbed by the material. So, while you may have wiped off or discolored the surface mold to the point that you can’t see it, you’ve actually provided plenty of water to regrow and possibly spread the mold beneath the surface.

Because we are not aware of peer-reviewed studies that assess the efficacy and safety of methods of mold treatment, including coatings and chemical sprays which do not meet the standard for “removal”, we do not currently recommend them. However, we are open to all information and would be happy to review new practices and products with independent third-party studies.



Our Experts
Carl Grimes – Carl has both the personal experience of how an unhealthy home created his own disabling health issues, plus professional experience in various industries working in the Indoor Air Quality (IAQ) field. Carl also wrote Starting Points for a Healthy Habitat in 1999, detailing possibilities of what could occur in a house to make its occupants sick, how to identify what was happening, and what to do about it.

Joe Medosch – Joe has almost 30 years of experience as a contractor and 10 years as a master trainer with expertise in home performance, particularly in health and energy-efficiency. His proficiency includes building science & diagnostics and Indoor Air Quality (IAQ) assessments. He has served on numerous committees developing industry standards including: RESNET Standard 380, Equipment Sub-Committee, and BPI multifamily standards development.



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Hayward Score Staff
Hayward Score Staff
Staff articles are researched, written, edited, and reviewed by the Hayward Score team and its network of advocates and subject matter experts.
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