Understanding Mold

Todd F. Shupe  |  10/8/2012 10:43:40 PM

This image shows mold (dark black areas) on the surface of wood.

The climate in Louisiana is ideal to promote mold growth in houses. This article provides information to some common questions about mold.

Several beams in my attic are discolored in areas. How can I tell if it's mold or decay?

Differentiating between mold and decay is very important -- mold fungi simply discolor wood, whereas decay fungi actually weaken the wood structure.

Several features distinguish mold growth from decay. Mold often appears as black, green or brown fuzzy or powder patches. Spores can also be gray, purple or red. Mold growth can easily be brushed, planed or washed off, and the wood beneath the discoloration is most often sound.

Decay may appear as unnatural brown or bleached areas in early stages of fungal infection, and it can be difficult to recognize. Brown-rot, the most destructive type of decay fungi, is characterized by darkening and shrinking of wood, with eventual crumbling in the advanced stage. White-rot, another common decay fungi, may cause wood to lose its color or appear bleached. The wood will not shrink or crack but will feel spongy in the advanced stage.

How can I discourage mold and decay fungi growth in my home?

Both mold and decay fungi thrive in areas with high humidity and poor ventilation. The following tips can help deter mold and decay fungi growth:

  • Increase ventilation in enclosed areas with fans and vents.
  • Run a dehumidifier.
  • Look for and remedy leaks in pipes and foundations.
  • Use paint containing mildewcide in high-moisture areas.

In new construction, certain design features can also help keep mold and decay at bay:

  • Adequate roof overhangs.
  • Properly ventilated crawl spaces and attics.
  • Proper flashing and moisture barrier installation.
  • Ventilating bathrooms to the outdoors.
  • Using exterior finishes that shed water.

There is no sure way to eliminate mold from your home, but following tips such as these can help you keep the upper hand.

I've discovered mildew growing in my basement. Is there an effective way to remove it?

Mildew is the common term used to describe mold and its discoloration on unfinished wood. To clean mildew from wood, you can use a commercially available cleaner or create one yourself using the following formula:

  • 1 quart household bleach
  • 1/3 cup powdered laundry detergent (Caution: Do not use liquid detergent or any other detergent that contains ammonia. Ammonia reacts with bleach to form a poisonous gas.)
  • 3 quarts warm water

Washing the affected areas with this mixture will remove most of the mold spores while renewing the look of the wood. Rinse thoroughly with fresh water and be sure to dry the area after cleaning.

Toxic Mold

First, one must understand how mold lives. Most mold requires simple things to exist and colonize. It requires some type of moist intrusion or humidity, otherwise known as "the wicking effect." In some cases, it can take as little as 24 hours for this process to begin. After the source of the moisture has stopped, it does not mean that the mold has stopped growing.

Some molds are cryophytes (these adapt to low temperatures), some are thermo tolerant (they adapt to a wide range of temperatures) and some are thermopiles (they adapt to high temperatures). Depending on the species, these microbes will grow just about anywhere. Mold requires a compatible temperature for each species. Environmental factors (temperature, nitrogen, oxygen, etc.) are necessary compounds for indoor molds to thrive.

Mold also needs an organic source of food. People might be confused because mold can grow on glass, tile, stainless steel, cookware, etc., but it is generally feeding off of some organic source deposited on this material (oils, films, dirt, skin cells, etc.). The fiberglass insulation people like to say that mold does not grow on their product, which is a fairly true statement; however, it grows on the organic debris that becomes trapped in their products. Mold also grows on things such as wood, fabric, leather, gypsum, fiberboard, drywall, stucco and many fibrous insulation materials.

All molds require some form of moisture to grow; however, like temperature, the amount of moisture varies for different species. Some are xerophillic (colonize under very dry conditions) some are xerotolerant (colonize under a wide range of moisture levels) and some are hydrophilic (colonize at high moisture levels). It doesn't have to be a leak. Humidity or moisture content of the substrate can often be sufficient (relative humidity over 50% start becoming problematic in many indoor cases). It can easily spread very easily through any HVAC system.

Mycotoxins are examples of chemical substances that molds create generally as secondary metabolites, thought to possibly play a role in either helping to prepare the substrate on which they exist for digestion, as defense mechanisms. Some have suggested that they may be produced when the organisms are under stress, which could be related to competition/defense. Or they simply may be due to inhospitable environmental conditions. The mycotoxins, which are also neurotoxins (a toxin that is determined to cause neurological damage), most commonly reach people from the air, via spores from the molds in question. They are also found in small particulates at times -- which may often represent mold dust -- small particles of mold that has dried and turned to dust. Spores, when inhaled, can begin to colonize in the sinuses and throughout the body, including the brain, lung and gut after a period of time.

One of the mycotoxins, aflatoxin, is produced by the fungi Penicillium, Aspergillus flavus and Aspergillus parasiticus. Four different aflatoxins, B1, B2, G1 and G2, have been identified, with B1 being the most toxic, carcinogenic and prevalent.

Another very dangerous family of toxin producers is Fusarium. The toxins zearalenone, trichothecenes or moniliformin can be formed by various types of Fusarium including F. moniliforme, F. oxysporum, F. culmorum, F. avenaceum, F. equiseti, F. roseum and F. nivale.

Under certain growth and environmental conditions, Stachybotrys chartarum may produce several different mycotoxins, including a very strong class known as trichothecenes. Trichothecenes are also produced by several common molds, including species in the genera Acremonium (Cephalosporium), Cylindrocarpon, Dendrodochium, Myrothecium, Trichoderma and Trichothecium. The trichothecenes are potent inhibitors of DNA, RNA and protein synthesis. They been well studied in animal models because of concern about their potential misuse as agents of biological warfare due to their ability to destroy human health (mentally and physically) and never show up in an autopsy. Sick buildings are one of the three major causes of fungal illness in industrialized nations today. Below are some things to be aware of.

Potential Sign

  • Stained ceiling tiles (you would be very surprised as to what may be growing underneath them) or walls
  • Musty, earthy or urine smell or odor
  • Black, brown, orange-pinkish or green speckled walls or around any plumbing grout or tile
  • Mild to severe unexplained illness
  • Swollen or crumbling walls or floor boards
  • Sewer backup
  • Leaky roof
  • Flood or hurricane damage
  • Leaky window or door

Mitigating Factors

  • Leaky roof
  • Flood or hurricane damage
  • Leaky window or door
  • Plumbing leak/faulty plumbing job
  • Water damage after a fire
  • Poor carpet cleaning job
  • Faulty air conditioning or heating system
  • Lack of proper ventilation
  • Clogged vents or air ducts
  • Construction defects; windows not seated properly, cracked foundations, etc.
  • Poor planning; lack of crawl space, sealed windows, no overflow spouts in sinks/bathtubs, carpeting in bathrooms, etc.
  • Cut-rate materials; substandard plumbing, inadequate siding, etc.
  • Location; flood zones, water table, environmental issues, etc.

This is not an all inclusive list, nor does it suggest you may possibly have any toxigenic molds. For more information, seek the advice of a professional.

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