The musty, unpleasant scent associated with a damp environment is caused by mildew, a common form of surface mold. This odor results from the fungus releasing gasses called Microbial Volatile Organic Compounds (MVOCs) into the air. The presence of MVOCs indicates active fungal growth and a persistent moisture problem. Addressing the smell immediately is necessary, as mold spores and MVOCs can lead to symptoms like headaches, nasal irritation, and fatigue in some individuals.
Pinpointing the Source of Moisture
The musty smell often travels through the air, so the strongest odor may not be directly at the source. Mildew requires a consistent water source and organic material to feed on, so investigation should focus on areas where water intrusion or condensation is likely. Hidden moisture often accumulates behind walls, under sinks, in basements, crawl spaces, and within HVAC ductwork.
Visual inspection can reveal subtle signs of a hidden problem, such as peeling paint, bubbling wallpaper, or discoloration on ceilings and walls. Drywall that feels soft or crumbly indicates long-term moisture damage and potential growth behind the surface. Using a moisture meter can help detect elevated water content in materials that appear dry.
Cleaning Solutions for Hard and Soft Surfaces
Once the moisture source is repaired and the visible growth area is located, the next step is the physical removal of the mildew. The appropriate cleaning agent depends on the surface material, distinguishing between non-porous and porous items. For non-porous surfaces like tile, glass, and sealed wood, a solution of household bleach is highly effective. Mix one cup of bleach diluted in one gallon of water, apply it to the surface, and allow it to sit for 10 to 15 minutes before scrubbing and rinsing.
Undiluted white vinegar is a non-toxic alternative that can kill many species of mold and is safe for most hard surfaces, but it must never be mixed with bleach.
Porous Materials
For porous materials like carpets, upholstery, or fabrics, bleach is unsuitable because the water content can penetrate the material and feed mold roots. Instead, use a solution of borax, mixed at a ratio of one cup per gallon of warm water, to scrub and inhibit fungal growth.
For heavily contaminated porous materials, such as drywall, ceiling tiles, or insulation that have been wet for more than 48 hours, removal and replacement is the most effective solution. These materials absorb moisture and mold spores deep within their structure, making them nearly impossible to clean thoroughly. After cleaning and removal, ensure the area is completely dried out before beginning any repairs.
Eliminating Residual Airborne Odors
Even after the mildew is removed and the moisture source is fixed, MVOCs and microscopic spores can linger, causing a persistent smell. Proper air treatment is required to neutralize these remaining odor molecules. Air purifiers equipped with a High-Efficiency Particulate Air (HEPA) filter can capture airborne mold spores.
To eliminate the chemical odor itself, the air purifier must also contain an activated carbon filter, which absorbs the MVOC gas molecules. For surface deodorizing, natural adsorbents like open containers of activated charcoal or baking soda can be placed in the affected area. In severe cases, professional intervention using an ozone generator may be necessary, but this process requires the area to be completely vacated due to safety concerns.
Controlling Humidity to Prevent Future Growth
The long-term prevention of mildew growth requires strict control over indoor moisture levels. Experts recommend maintaining indoor relative humidity (RH) between 30% and 50%, a range too dry for mold to grow. Monitoring the RH with a hygrometer is the first step in maintaining this balance.
Using a dehumidifier is an effective way to lower moisture content, particularly in damp areas like basements and crawl spaces. In high-moisture areas like bathrooms and kitchens, use exhaust fans that vent air directly to the outside to remove steam. Furthermore, ensuring that furniture is not pushed directly against exterior walls promotes airflow, helping prevent localized moisture buildup.