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When Does a Moisture Problem Become a Mold Problem?

Is it mold, mildew or just the smell of an old house? How do you know if moisture you see on the walls or in the basement will become a toxic mold problem? Read on to find out.

How do molds get in the indoor environment and how do they grow?

Mold spores may enter your house from the outside through open doorways, windows, and heating, ventilation, and air conditioning systems with outdoor air intakes. Spores in the air outside also attach themselves to people and animals, making clothing, shoes, bags, and pets convenient vehicles for carrying mold indoors. Outdoor molds are generally more abundant and impact allergies more than indoor molds.

The most common types of mold that are found indoors include: Cladosporium, Penicillium, Alternaria, and Aspergillus.

Stachybotrys chartarum (also known as Stachybotrys atra and sometimes referred to as "black mold") is a greenish-black mold that can also be found indoors. That is the problem mold.

Wet cellulose materials, including paper and paper products, cardboard, ceiling tiles, wood, and wood products, are particularly conducive for the growth of some molds. Other materials such as dust, paints, wallpaper, insulation materials, drywall, carpet, fabric, and upholstery, commonly support mold growth.

Most fungi generally are not pathogenic to healthy humans. (Despite what’s shown in The Last of Us.) It is estimated that about 10% of the population has allergic antibodies to fungal antigens. Only half of these, or 5%, would be expected to show clinical illness.

How do you know if there is a mold problem in a home you are considering buying?

  • Large mold infestations can usually be seen or smelled.

  • Look for water damage and check the disclosure statements.

  • Recently patched ceilings could be covering recent leaks.

If you think there is a mold problem, ask to have a mold inspection included with normal inspection. You can also have the walls tested for moisture with a simple hand-held device to determine if are leaks that you cannot see that may present problems in the future.

When is it NOT mold?

  • A musty smell could be coming from water-damaged boxes or it could be the stale smell of a closed up house.

  • Don’t mistake the whitish crystalline or powdery deposit on damp masonry walls for mold. It is efflorescence or "mineral salts". This usually white fluffy material is left behind as moisture comes through the wall and evaporates into the building interior.

Efflorescence (shown above on cinderblock walls) is not mold, though it is an indicator of wet conditions that could contribute to a mold problem somewhere in the building. If you are not certain, ask your home inspector, or consult a specialist.

The test came back positive for some “toxic” molds. What is the next step?

First, address the source of the moisture. Have roof or foundation repairs done so that the problem will not recur after remediation. Hire a remediation specialist to remove existing mold and treat surfaces to prevent a reoccurrence. Their process should include:

  • Set up isolation barriers, negative pressure system, and drop cloths necessary to protect the structure during initial response activities.

  • Remove porous materials with visible growth

  • As they are removed from walls and ceilings, cut building materials in sections small enough to fit directly into waste bags. Bag all waste immediately rather than allowing it to pile up on the floor..

  • Clean all non-porous materials that have visible fungal growth.

  • Use a dehumidifier.

  • Apply antimicrobial coating to exposed structural members to prevent future mold contamination.

  • Have the HVAC system cleaned.

To establish that the home air quality is now acceptable, a third party should conduct a post-remediation verification sampling.


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