"What is mildew?" The answer depends on whether you ask a scientist or a nonexpert. Mycologists, who study fungi, use the term "mildew" only for fungi that grow on plants. When mycologists say "Mildew," they mean the white growth that causes diseases in plants.

People who are not scientists use the term "mildew" differently. For them, mildew is the discoloration caused by mold in buildings. The molds that grow around windows or in bathrooms are called "mildew."

Is mildew different than mold? The mycologist would say they are different. Mildew only grows on plants outdoors. The nonexpert, however, sees the effects of mold growing indoors and calls it "mildew."

To be more specific, we should ask, "How long does it take for a mold spore to germinate?" Then we should ask, "How long does it take growing mold to colonize?"

To grow, molds need a food source, a certain temperature and moisture. Where these conditions are present, molds can germinate and colonize. How fast growth occurs depends on the combination of conditions. Spores can germinate after only 12 hours in some conditions and some grow in 24 to 48 hours. Houses offer an ample food supply—drywall, wood, insulation, paper. When these materials become damp or wet, settled spores can become growing molds.

Molds may colonize in 1 to 12 days depending on the type of mold. Following are several types of molds and the number of days in which colonization may take place:

• Mucor sp. colonizes between 1 and 2 days.
• Rhizopus sp. colonizes between 1 and 2 days.
• Aspergillus sp. colonizes between 2 and 3 days.
• Penicillium sp. colonizes between 2 and 3 days.
• Stachybotrys chartarum colonizes between 8 and 12 days.

The musty odors produced by molds are known by scientists as Microbial Volatile Organic Compounds. (These compounds are abbreviated as mVOCs.) Some mVOCs produce musty and moldy odors, which result from the chemical changes taking place during the mold life process. They are waste products given off by actively growing molds. Health effects such as headaches, dizziness and nausea have been linked to exposure to mVOCs, but research is only beginning. Odors from mVOCs are a sign that mold is actively growing and so may indicate a level of mold contamination requiring remediation.

Mycotoxins are poisonous substances. "Myco" means fungus, so think of mycotoxins as "fungi toxins." They are designed for chemical warfare against other organisms, even against other types of molds. Living molds may produce mycotoxins to discourage other molds or bacteria from growing in the same territory. Unfortunately, humans who inhale, ingest or touch mycotoxins may have a toxic reaction. Some mycotoxins have been shown to produce human health effects, while little is known about the possible harmful affects of some other mycotoxins.

We should not panic over mold toxins. Not all molds produce mycotoxins; furthermore, molds that can produce mycotoxins do not produce them in all situations. EPA cautions that finding molds in a building does not mean that mycotoxins are also in the building, and even when mycotoxins are present in a building, the quantities may not be large and thus health threatening.

To prevent mold spores from spreading to clean areas of a building, a remediation contractor must control air movement. Two important procedures are (1) erecting critical barriers and (2) establishing negative pressurization in the work area.

Critical barriers block the paths that airborne mold spores might follow. Contractors construct critical barriers by placing two layers of polyethylene over any air pathways through which spores might travel (i.e, air vents, wall plates, recessed lighting, doors and other openings).

To establish negative pressure, a contractor creates low air pressure in the work area. The result is that rooms and areas surrounding the work area will have higher air pressure than the work area. Maintaining negative air pressure prevents mold spores from being carried by air movement from the work area to uncontaminated rooms of the job site.

The American Conference of Governmental Industrial Hygienists do not recommend using ozone on visible mold growth. Due to various factors, ozone has not been found effective against molds. One problem is the elements that cause ozone to be less effective. Ozone can be affected by temperature and pH, decreasing its impact on mold. Organic materials in the structure can also affect ozone.

A second problem is that ozone does not kill what it does not reach. No method of application can ensure that the ozone contacts every surface where mold contamination exists.

The last problem is mycotoxins. Even if ozone did affect mold, the toxins on mold spores and mold fragments still remain on surfaces and can still cause allergenic reactions in people. To remediate a mycotoxin problem, you must reduce the concentrations of mycotoxins in the structure.

In summary, ozone does not work with molds. In addition, molds are usually found in wet environments. Using ozone on wet materials in a wet environment may result in the bleaching of surfaces.