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Deep Breath: Monitoring the Moisture in Our Homes

Deep Breath: Monitoring the Moisture in Our Homes

In the last article, we discussed the moisture content of building materials.  It is important to monitor the moisture of materials because we don’t want any mold growth during the construction process, or as we occupy the home or building.  New homeowners depend on the builders to construct a home that is safe to live in.  So, lets talk about the timeline for mold growth and what are the typical contaminants we find.

When there is a claim submitted by a homeowner that a water release has occurred in their home,  insurance companies want to have the water damage restoration company onsite within a few hours of notice.  The reason is that everyone (should) know that naturally occurring mold spores that are in the air (all the time) will begin to germinate and grow in about 48 hours after coming in contact with elevated moisture or humidity.   Then nine days after they germinate, the colonies will be mature enough to produce their own spores.  Therefore, eleven days after the initial water release, there will be a large production of spores in the building and growth will really begin to take off.

Homeowners often ask me “if mold is growing here, will it start growing there?” I always say no, unless, the surface on the other area is also elevated in moisture. Be aware that the growth in the other area will happen anyway from the naturally occurring spores that are already in the air; it does not have to be associated with the current growth problem.

There are tens of thousands of mold genus/species in nature.  It is interesting that when you collect samples from a building that has recently had a water event, you normally see the same four or five types.  I wanted to briefly talk about each one these; all considered a Class I allergen (it is how the body responds to an allergenic contaminant):

Alternaria:  There are 40 or 50 species in this genius.  It can grow on organic debris, food stuffs and clothing.  It causes flu and hay fever symptoms, also hypersensitivity to this mold’s mycotoxin. This is the most common fungi in the world and generally black or olive grey in color.  When you go to a doctor’s office and are tested for allergies, the Alternaria mycotoxin is the one used to test you for mold sensitivity.

Cladosporium:  There are 28 to 40 species in the genius.  This is found on plants, potting soil in house plants, also on wood, clothing, painted surfaces, and paper.  It causes flu and hay fever symptoms, also hypersensitivity to this mold’s mycotoxin. This is an extremely opportunistic mold and will grow on any organic material that is moist.  The color is normally a light brown or yellow.

Aspergillus/Penicillium:  The reason these two genus are normally reported together is because you cannot tell them apart unless you grow them in a petri dish under laboratory conditions. There are about 200 species in each one of these genius, and they grow in the same locations and moisture conditions. They both cause flu and hay fever symptoms, also hypersensitivity to the mycotoxins. Aspergillus causes what is referred to as “farmers lungs” because of its tendency to grow on straw and Oat grain. Penicillin was discovered from the green mold that grows on bread and began the study of antibiotic chemistry in the pharmaceutical industry.

There are commonly around twenty molds that could easily be found in samples submitted to a laboratory from a newly water impacted building.  Some molds germinate quickly and grow fast, others take a few weeks to germinate and then slowly replace the faster growing molds.  People often ask when did mold began growing on a surface and how long it has been there.  This is a question that cannot be answered too often.  Mold colonies will grow where there is water, and then they will go dormant when there is not enough moisture to sustain them.

When you go into a space and you smell that musty odor that is associated with mold, all that tells you is there is mold present and there is enough water for it to grow.  You are not allergic to the odor you smell, that is a volatile organic compound that is an off-gas from growth, you are allergic to the spores and debris that you cannot smell.  You can go into buildings that are heavily contaminated with mold growth, but because it is dry, you cannot smell anything (but you had better be wearing a respirator to avoid the exposure affects).

When you go to the store and want to test your home for mold contamination, get the sampling equipment that uses a microscope slide; it is referred to as a “tape lift” sample.  You go up to the surface and press the sticky surface of the slide against the moldy surface and it will transfer to the slide.  The laboratory puts a stain on the slide and directly reads what is there. There are no special handling needs to ship the sample.

The sampling technique that uses a petri dish does not give good results for you. There is an ASTM standard for collecting this type of sample (called a viable sample technique) and you cannot follow this standard with the equipment you buy from a store.  For example, you need to know how much air the paste (called agar) in the dish has to be exposed, and then refrigerated, and shipped overnight to the laboratory.  This prevents the spores from germinating until it is placed is an incubator with a standard temperature and humidity that all laboratories use.  Otherwise, you cannot tell the difference between naturally occurring molds, and what is a contaminant in your home.  To make things more complicated, there are different agar pastes for different mold spores.  You may not see a serious contaminant because you used the wrong agar. For this type of sampling, you need to hire someone because it takes specialized equipment and training.

I want to mention that you do not need to know what kind of mold you are looking at unless there is an extenuating circumstance.  The technical approach for removing it does not depend on what kind it is.   In many cases all you need to soap, water, and a rag.  Remember that you don’t care about killing mold growth, just removing it and determining why the surface became elevated in moisture.  Don’t use bleach!! That is such old news.  We will talk more about removing mold from your home in a future article.

If you have any questions or would like to hear about a certain topic, you can reach me at  I will post some of the questions asked at the end of the next article.

Bob Bennett is the President of Farsight Management, and the President of the Indoor Air Quality Association for North East Ohio.  He has been provided indoor air quality consulting and abatement for the last 20 years to builders, homeowners, insurance companies, and property management companies.  You can follow Mr. Bennett on Facebook under Farsight Management; he frequently posts comments on interesting projects and articles of interest. Contact him through his email if you have any questions.

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