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Investigating & Remediating Indoor Mold Problems

Although there has been growing concern, since the mid-1990s, about the potential health effects of mold growth in indoor spaces, mold is not some new, alien threat that has recently become a problem.  The fact is, mold and mold spores are everywhere in our natural environment, and always have been.  So what's behind the recent "explosion" of mold problems?  There's a few things going on:


  • Up until the late 1970s and 1980s, most buildings "breathed"... there was abundant infiltration of fresh, outdoor air into buildings, which diluted and purged any indoor air contaminants.  This all changed when energy conservation measures dictated that buildings be "tight" to minimize the loss of artificial heating and cooling.  Today, modern energy-efficient construction methods can lead to excess indoor humidity which can promote mold growth, and tend to trap air contaminants within the indoor environment.


  • In the past, in the United States, most building construction typically used mature old-growth wood.  This all changed in the 1980s, when ecological restrictions caused the wood-products industry to start using predominantly younger trees.  Young wood has less compact growth rings (grain), and often has much higher polysaccharide (sugar) levels, than old-growth wood.  Both of these conditions can make wooden building construction materials a more inviting substrate for mold colonization and growth. 

  • To stretch available wood supplies, and to make lighter, stronger, and more cost-effective building materials, the use of "engineered" wood products became common in the 1980s and 1990s.  Things like oriented-strand board (OSB), chip and sawdust composite sheathing and siding products, came into regular use, replacing previously-used whole lumber and plywood panel products.  These engineered wood products, if they get wet, turn into what the mold abatement industry calls mold chow.  They can very effectively promote and sustain extensive mold growth. 

  • And building construction methods have changed too.  Prior to the 1980s, building construction was typically seasonal, with most construction occurring during the summer months.  It was very uncommon for the shell of a building to be constructed and closed-up during the local wet season.  Today, buildings are constructed year-round, and are often closed-up after extensive exposure to rain, snow, and/or ice.  There's no amount of heaters that can satisfactorily dry out a building that has been exposed to these conditions... and so all that moisture ends up getting trapped inside the structure where it's just a matter of time before a mold growth problem becomes apparent.


So what exactly is mold?  Mold is a fungus (plural = fungi), not all that different from mushrooms and toadstools.  The vegetative or growth portion of mold is the mycelium, which is made up of a network of branching hyphae.  At a certain point in its life cycle, the mold will produce stalks that contain spores.  When the spores become mature and are released, they travel in air to settle onto new surfaces which hopefully have conditions which are favorable to allow the spores to germinate and start new mold colonies.


As said previously, molds are part of the natural environment and are pretty much everywhere.  All a mold spore needs to germinate and start growing are:

  • a source of food

  • a comfortable temperature, and,

  • moisture

Our indoor environments provide abundant food (often cellulose from wood- and other plant-based products) and moderate temperatures.  So all one has to do is add water, for example from excessive humidity, a plumbing leak, or a roof or window frame leak, and mold will begin to grow and probably thrive.


Fungi produce mycotoxins... defensive chemicals to prevent bacteria from over-growing the mold colony.  It is the mycotoxins in the mold spores and mycelium that can provoke a wide variety of adverse health reactions:


  • Most people have little to no reaction, although exposure to very high levels of spores and mycelium fragments might provoke mild irritation of the eyes and nose.

  • A significant sub-set of the population will experience allergy-like reactions when exposed to mold.  These reactions can range from relatively mild (itchy skin; rash / blotchiness; runny nose; watery eyes), to asthma-like symptoms (constricted bronchi; wheezing), to all-out anaphylaxis.  Remember, most antibiotics are derived from molds, so anyone with an allergy to say penicillin is going to have a potentially-dangerous reaction to at least some types of mold.

  • Some mold mycotoxins are psychogenic... they can cause cognitive distortions and hallucinations (no surprise; LSD is a mold derivative).   I have investigated mold exposure incidents where one of the reported symptoms of exposure was very vivid hallucinations.

  • Some people become extremely sensitive to mold after a single, high concentration exposure.  For other people (even those with no initial reactions to mold exposure), it is repeated exposures that can result in progressive sensitivity.  Unfortunately, there is no way to predict how any one individual will ultimately respond to mold exposure.

  • A few people will become hypersensitive to mold... even the tiniest amount of mycotoxin will set off a potentially devastating physiological reaction in them.  And still other people find their immune systems have been (presumably) permanently damaged by (usually) long-term exposure to mold.

So, what do you do if you think you might have an indoor mold problem?

The first step is to confirm that mold / mold spores are actually present at unacceptable levels in your indoor environment. 


One investigative method is to wipe indoor surfaces, and have the number of spores recovered determined by an analytical laboratory.  While surface sampling can be a relatively fast and easy screening method to determine if there is a serious mold problem, it is rarely sensitive enough to identify "typical" indoor mold growth problems.

The "gold standard" for mold testing is air sampling.  Samples of air are passed through a special filter cartridge, or impinged upon a culture plate, and the analyzed by a laboratory.  Air testing can potentially tell you:


  • approximately how many spores and/or mycelium fragments are dispersed in indoor air,

  • the type (genus and species) of molds that are present,

  • whether the spores that are present are capable of germinating (an indicator of whether there is currently active mold growth in the building).

The concentration of spores in the indoor environment should never significantly exceed the concentration present in outdoor (ambient) air.

If a mold problem is confirmed, the next step is to identify and correct the source of the mold.  This can often involve opening wall and ceiling cavities to find hidden mold growth.  As indicated before, mold growth requires moisture.  So once the area of mold growth is found, it is imperative to correct whatever problem(s) led to mold growing in the first place (i.e., correcting any leaks or sources of excessive humidity).  There is absolutely no point to trying to eliminate mold growth (e.g., cleaning; disinfection) if the source of the problem is not corrected, as the mold will return in a very short period of time.

Once the area of mold growth has been identified and the source problem corrected, it's time for cleanup.  There's three different terms in common usage:

  • abate

  • mitigate


Both of these terms have similar meaning:  To reduce or remove a nuisance or hazard.

The third term is remediate, which has a slightly different meaning:  To restore by stopping or reversing damage.

In general, it is not that important which term is used... the outcome should be the same.  The goal is to remove any moldy and/or damaged material, clean, disinfect, and possibly treat areas where there is the possibility of any residual mold.  When all mold and mold damage has been abated, reconstruction of spaces and cavities that had to be opened can occur.  It is noted that mold remediation is not something for an amateur or do-it-yourselfer.  Without use of proper containment methods and equipment, amateur/DIY mold removal is likely to just spread the contamination throughout the building and make matters much worse.

Because mold spores and fragments can be dispersed by air currents throughout an indoor space, the entire affected indoor space, and all contents within the space, need to be carefully cleaned and disinfected following remediation activities.  And after cleanup, a round of post-remediation air sampling must be conducted to confirm that the project has met its goals, and that the involved indoor spaces can be "cleared" as safe for re-occupancy. 


Final Thoughts

A few things to consider if you think that you may be dealing with an indoor mold growth problem:

  • Avoid using a mold abatement contractor to conduct your initial assessment sampling.... it's just a potential conflict of interest.  All sampling should be conducted by a fully independent party who has nothing to gain from the results.

  • Be cautious about who you hire to do mold sampling.  Just because someone has all the sampling equipment, and is reasonably competent at using it, doesn't mean that they are experts at evaluating a potential mold problem.  Too often we've seen sampling "technicians" submit pretty much incomprehensible analysis reports to people, with no explanation as to what the results potentially mean.  You need to hire people that understand mold, who can fully explain to you what the sampling results mean, and who can make reasonable recommendations as to what (if anything) needs to be done to correct the problem.

  • Do not get talked into a costly, possibly unnecessary, mold abatement project.  Always seek at least one or two independent opinions, from qualified professionals, before committing to a major mold abatement process.

  • If you in fact are dealing with a significant mold growth issue, you are probably going to need an interdisciplinary team of professionals to correct the problem(s).  The team will often include industrial hygienists, microbiologists, a mold abatement contractor, and possibly also a construction contractor.  And because a mold abatement / remediation project can be very complex and somewhat overwhelming in scope, you may also want to hire a project manager: Someone to prepare the scope of work, coordinate all the participants, validate the procedures used, work completed, and results obtained, and document the project and certify that the work has been completed to acceptable standards (a final project report).

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