With the weather we’ve been having this summer; hot, very humid with thundershowers and occasional prolonged downpours, there has been an increase in requests for indoor air quality assessments, especially mold inspections. In the course of conducting these inspections it seems there are many questions that come up over and over again for homeowners. This blog post is intended to address many of those common questions as well as give an overview of what is needed when mold contamination of an occupied building occurs.
Inspection of building & building envelope
The first step to be taken whenever mold contamination of a building interior is suspected is to determine the presence and source of moisture intrusion. Since the presence of mold spores, food sources for mold and optimal temperature ranges for mold growth are universal in occupied buildings, the one factor that is critical that we can control is moisture levels.
Determine the source of moisture
For moisture to reach levels conducive to mold growth (>/=17%) the source may not be readily apparent. But that is where we begin in our visual inspection; determining the source of the moisture. Unless there is a failure of either water supply or waste systems (plumbing leaks don’t have to be great to cause a problem), the source will typically be moisture intrusion through the building envelope. Penetrations in the building envelope such as entry/exit sites for pipes, chimneys, windows, doors, and foundation cracks are common points of entry for water. Other sites include where dissimilar types of building materials abut, such as where the wood framing meets a concrete foundation, or where roofing meets wall siding or skylights. Moisture, on the other hand, can penetrate seemingly impervious surfaces such as concrete walls and slabs (even when no cracks are present), brick, siding, stucco, EIFS (exterior insulated finishing systems – usually with synthetic stucco) and roofing systems.
Moisture intrusion requires a point source (typically atmospheric or ground); a mechanism (typically liquid or vapor movement), a route of entry (gaps and penetrations, air permeable layers, vapor permeable layers or porous materials), and a driving force (kinetic energy, gravity, air or vapor pressure gradient, temperature gradient or surface tension). When moisture intrusion is low or intermittent, in order for moisture levels to reach a threshold necessary for mold growth to occur, moisture accumulation is required. This occurs when the rate of wetting exceeds (or is lagged by) the rate of drying and the difference exceeds the safe storage (buffering) capacity of the building materials present. When moisture accumulation coincides with sufficient temperature and time, then problems occur–including mold, decay, rust, swelling, warp-age, delamination, truss uplift, efflorescence, freeze-thaw damage, loss of thermal resistance, and insect infestation. Within an optimal temperature range (the same temperature range we prefer for comfort in our living spaces), it doesn’t take long for mold to begin colonization once the 17% moisture threshold is reached.
A good quality moisture meter is important in assessing problem areas, especially when visible signs of water intrusion are not evident. For example, vapor diffusion through concrete can result in moisture levels high enough (>/=17%) to support mold growth in the presence of an organic material that can serve as a food source for the mold. This is especially true when there are building materials such as carpeting, laminate flooring, framing, drywall or other materials adjacent to the concrete that limit air flow over the surface of the concrete and allow moisture to accumulate while at the same time providing organic material as a food source for the mold.
Use of the moisture meter* to assess areas of concrete with high vapor diffusion and/or high moisture levels can be very helpful in pinpointing problem areas on foundation walls, subsurface concrete slabs, and even on-grade slabs in areas where soil moisture levels are high. High moisture levels in concrete foundations and slabs can also occur through condensation from air with a high relative humidity coming in contact with the cooler concrete surfaces. This is especially common in the summer in areas where relative humidity is high and there is a substantial temperature differential between the outside air and the below-grade concrete of the foundation and slab.
Isolating hot, moist outside air from contact with cooler concrete surfaces may be necessary in determining the source of the moisture in the concrete. One easy way to do this is to perimeter tape (aluminum foil duct tape is good for this) a polyethylene (PE) sheet of at least 6 mils thickness and at least 9 square feet to the concrete. Monitor for at least four days in a row, thoroughly removing any moisture from the slab side of the PE each day. If the moisture is diffusing through the slab, you will continue to see fairly uniform condensation of moisture on the slab side of the PE each day. If the condensation appears to be tapering off continue to monitor longer to assess if the condensation might also be diffusing through the slab but with condensation from the air being the primary source. Limiting moist, outside air from this area and concurrent use of a dehumidifier during this process can be helpful in this assessment process as well.
*A top quality moisture meter uses state-of-the-science electromagnetic wave technology to measure moisture levels up to 3/4 of an inch into building materials, even concrete. And it will have settings that allow for differences in building material densities. A good quality meter will cost more but will give more reliable readings. I recommend the Wagner BI 2200.
Once you have determined where the suspected problem areas are located, testing for the presence of mold is indicated. The two best tests, in my opinion, for these areas are tape lift method and swab. Both of these are used to collect samples that upon microscopic and/or culturing can provide specific data about mold species present, viability of spores and concentration in terms of colony-forming units. Each of these tests has its advantages and its limitations.
The tape lift method is typically used in areas where there is visible vegetative growth and is used to collect mold hyphae (hair-like strands), surface mycelia (root-like strands), and spores. Specially-prepared tape lift kits are available from licensed microbiology labs that are used for this type of collection. Tape lift specimens are analyzed qualitatively by a licensed microbiologist to determine the types of mold present. It does not indicate the viability of the mold (Is it alive and able to reproduce?) or the number of colony-forming units (the severity of the contamination.) Knowing the types of mold present is key in determining the methods of remediation and/or abatement necessary to protect building occupants, prevent the spread of the mold to non-contaminated areas of the building, and how radical the abatement methods need to be as far as removing and safely disposing of contaminated materials.
The swab test uses essentially the same procedure that a doctor uses to determine if you have strep throat. The only difference is that we are testing for mold, not bacteria. A sterile cotton swab is used to swab a small one square inch area (instead of your throat) that is suspected of mold contamination. The swab is then immediately sealed in a sterile tube containing food and moisture and shipped to the lab. At the lab it is swabbed onto a petri dish and placed in an incubator to grow any mold that might have been present at the test site. Once a growth is established, a licensed microbiologist examines it under a microscope to identify the types of mold and count the number of colony-forming units which indicates the extent of contamination at the point where the specimen was taken. This test will only show those mold types that are viable (living and capable of producing more mold, either from live mold or live but inactive spores.)
Other methods include air sampling used to collect particulate from the air and then compare indoor to outdoor air counts, and bulk sampling of specific materials that appear to have vegetative growths on them to obtain counts. Neither of these recognize the viability of mold growth, only the presence of mold. For these reasons they are not used as often. The swab/culture test, in my professional opinion, is the most valuable and provides the most useful information.
The number one factor you can control in eliminating or preventing mold is moisture. Until you eliminate the source of moisture for the mold, you are wasting any money on doing any remediation – the mold will return. Using an air purifier with radiant catalytic ionization (RCI) to protect building occupants and remediation/abatement workers however is valuable once samples have been collected. Don’t use RCI prior to collecting samples or you will be unable to identify any mold from your swab tests!
Protect building occupants
As important as it is to reduce moisture levels, one concern in doing so is that the mold will dry out, go into a spore-forming state and release spores into the air. Spores are seeds for the mold: they are inactive but given the right conditions can produce more mold. Spores are able to withstand extreme conditions and still produce live mold even years later when the right conditions exist. They are also lightweight and become airborne very easily, traveling on air currents throughout a building. Hyphal fragments can also become airborne and inhaled by building occupants.
Note: some spores such as stachybotrys contain mycotoxins, others are a source of foreign proteins that can irritate the airways in the nose, throat and lungs, sensitizing individuals and causing reactions and allergies. Repeated exposure often causes increased sensitivity and exacerbation of symptoms. (First and foremost, testing should be done to determine mold types and quantities present. The type of mold is indicative of the threat to building occupants and will determine the level of abatement/remediation required.)
Remediation: a three-prong approach
Because of this, once the moisture intrusion is stopped, I recommend a three-prong approach; concurrent dehumidification of the building; application of airborne RCI-produced purifying plasma of oxidizers to kill mold and inactivate spores as well as reduce airborne particulates containing spores and hyphal fragments; and mechanical cleaning of the mold, including application of biocides and removal of moldy items that cannot be easily treated with biocides and/or easily replaced. Remediation/abatement should always be done by trained and insured professionals. Don’t risk spreading contamination or compromising your health with exposure to airborne mold.
To prevent airborne spread of the spores which can contain mycotoxins it is important to isolate the contaminated area through the use of mechanical barriers (such as polyethylene sheeting) and use of HEPA-filtered ventilation of the contaminated area to create negative pressure within the isolated space. Care should be exercised when dismantling containment areas to prevent spreading and inhaling any spores or hyphal fragments trapped in the containment barriers and equipment. Even though the mold and spores have been inactivated by oxidation and killed by the biocide, if inhaled they can still cause sensitization and airway irritation. Mycotoxins may also still be present even though the mold is dead. Care and thoroughness is of tantamount importance.
Clearance swab testing should always be performed following abatement/remediation to be sure the problem has been effectively remediated. Do this before any repairs are made or new construction is begun except for repairs needed to prevent water intrusion.
For more information contact:
Mike Hedrick, CMI
Indoor Environmental Consultant
Certified Mold Inspector
Healthy Living Technology