ICS Magazine

Post-Remediation Treatments for Mold

November 8, 2005


Q: I read that there is a product that can be applied to a building that will kill the residual mold left after normal remediation. Is there any reason why we shouldn't use them?

A: Actually, there are a number of products on the market that are being sold as post-remediation treatments. Some are being sold as the "solution" to the entire remediation process. Since I am not sure which one of the products you are referring to, I can't address how it works or if there would be any benefit in using it. I can, however, address some of the issues that I have in determining whether or not these products are effective. For the sake of discussion, let's call the products "biocides" or "post remediation treatment" even though they might be an antimicrobial.

Before we discuss the effectiveness or appropriateness of these applications, let's develop the groundwork for the discussion. First of all, we have a mold problem that needs to be remediated. Most remediators agree that the use of these "spray on" or "fogged in" biocidal products should only be used as a post-remediation application, which means that some form of physical removal has to be performed prior to the treatment. There are companies that are using spray-on biocide applications as the entire remediation process; however, if the EPA has not registered the product for this kind of application, it is not appropriate. In addition, the EPA typically tests products on clean, dry, non-porous hard surfaces.

Generally, the intent of the post-remediation application is to deal with the residual or inaccessible mold growth. The remediation is being performed to protect the built environment and the occupants. Occupants that might have an adverse reaction to the mold will have an allergic, toxic or pathogenic response. By far the most common reaction is allergic; next is toxic and the least common is pathogenic. In fact, it has been argued that, outside of hospitals and convalescent homes, pathogenic reactions may only account for less than 1 percent of all adverse reactions, as pathogenic reactions can only occur if the mold is viable and able to grow in the host's body.

In speaking with those that promote these products, I am usually told that an environmental consultant (EC) has performed sampling and determined that the remediation was a success. My first question is, "Did anyone try sampling prior to the application of the biocide?" What I am trying to determine is whether it was the cleaning or the treatment that was in fact what caused the environment to be successfully remediated. If the area being remediated was already clean, then the application of the biocide provides little or no benefit.

Where culturable sampling has been performed, we often find that the sampling strategy was designed to determine whether or not the post remediation treatment was successful in killing the mold. An April 2004 study published in the "Forest Products Journal" reviewed the ability of bleach and four other biocide treatments to remove and prevent mold growth on Douglas-fir lumber. The study concluded that, "While bleach is often recommended for remediation of surface mold on wood, our results illustrate that the treatment does not eliminate the surface microflora." It goes on to state that, "None of the treatments inhibited all of the fungi present. These treatments were selected because they are being touted as mold treatments and because of their relatively low toxicity profiles that would allow their use without a pesticide applicators license. However, it is clear that these treatments lack the broad spectrum activity required to reduce the activity of such a diverse microflora."

Let's assume that they are effective in killing the mold. What benefit is there in accomplishing this task? Essentially, there is very little benefit. Referring to the groundwork established in the second paragraph, the only benefit is that now the molds are not capable of causing a pathogenic reaction. Dead mold is still potentially capable of causing an allergic and toxic reaction. By killing mold, we reduce the ability of molds to cause an adverse reaction by less than 1 percent.

When making this observation recently, I was told that, "since this was a post-remediation treatment, that there was very little mold left and therefore it was unlikely that anyone would have a reaction anyway." If you think about the argument for a moment, you must conclude that since "there was very little mold left anyway" and that "it was unlikely that anyone would react" then why spend the time and money to perform the treatment? What would be the benefit?

There have been some post-treatment spore-trap sample data and tape lifts that reportedly indicated there was no mold present after the remediation and application of the biocide were complete. These post-remediation treatments are designed to kill mold, not to make it disappear. If the spore-trap data and tape lifts show that there is no mold present, it is because the molds were physically removed by some process such as the HEPA vacuuming and detailed cleaning that typically occurs in mold remediation. If it isn't there, there is no need to treat it.

There is one other final consideration regarding the application of encapsulant-type products. According to the IICRC S520 Standard and Reference Guide for Professional Mold Remediation: "It is highly recommended that remediators consider that applying certain antimicrobial products may change the permeability of materials and may trap moisture, thereby resulting in future deterioration, along with associated potential liability."

One of the considerations taken into account when deciding to employ post-remediation treatments is to help limit liability. The best defense is to make sure surfaces are clean and dry in accordance with the peer-reviewed standard of care set forth in the IICRC S520 Standard and Reference Guide for Professional Mold Remediation.